Is Home Birth Safe?

This is another entry in my series on Pregnancy and Birth Outcomes based on the Washington state birth certificate data.

The Business of Being Born Again has just been released.  Which of course sparks the never ending discussion on whether home birth is safe or not.  I have not seen the new documentary, but the original Business of Being Born makes the premise that hospital birth is more dangerous than home birth because of the overuse of interventions, specifically induction, augmentation and an epidural.  The movie states that even women who want to avoid these interventions are pressured into them by the care providers in a hospital for a variety of reasons, including that it is more convenient for the staff, and they make more money.

I have been working on this analysis for a long time.  I kept waffling on whether it would be better to post analysis of each type of intervention, and then home birth, or vice verse.  I struggled getting the most fair, accurate, and mathematically correct analysis, and of course making all the data presentable and understandable.  I am also a bit scared because this is a topic that can get heated and I would prefer not to be the target of a barrage, but I think this information is important enough that I am willing to put myself out there.

Once again I'll start with the conclusion and work backward for the googlers who need answers at the top of the page ;)

CONCLUSION
In Washington state midwives are licensed, regulated, and are able to carry life saving medications that include anti-hemorrhagic, anti-seizure medication, intravenous fluids, epinephrine, oxygen and antibiotics for the treatment of group B strep infection.  Home birth is legal and is required to be covered by insurance (if the insurance covers maternity care).  Under these conditions from 2002 - 2007 for babies born between 37 - 42 weeks gestation home birth had overall better outcomes for both babies and mothers than low risk births that took place in a hospital.  Even when compared to births at a hospital that were not induced, augmented or made use of an epidural, births that took place at home had overall better outcomes for babies and mothers.   


RESULTS

Results highlighted in yellow are considered statistically significant, while those that are not highlighted are not considered so.  Click on the small thumbnail to see the table that includes the confidence intervals.

Home Birth With Attendant:  Births that happened at home or were planned on happening at home with the supervision of a care provider.  The care providers were mostly licensed midwives, but also included certified nurse midwives, osteopaths and doctors.  The births were between 37 - 42 weeks gestation.  I did not restrict the results to low risk, so the data includes VBAC's and other complications that the attendant apparently felt comfortable enough to attend the birth at home.

Low Risk Hospital: These are all the births that happened at a hospital and were planned to happen there. The births were between 37 and 42 weeks gestation.  Only low-risk patients were included in the data set so women that had  diabetes, hypertension, previous preterm births, other previous poor pregnancy outcomes, vaginal bleeding during this pregnancy prior to the onset of labor, pregnancy resulted from infertility treatment, had previous cesareans, Group B strep, were carrying multiple babies, had an incompetent cervix, had preterm labor, had a external cephalic version, received steroids (glucocorticoids) prior to labor, or the baby was breech or transverse were excluded from the data.

Click to enlarge

Click here to view all data including confidence intervals.

• The rate of adverse outcomes for the baby were approximately 6.5 percentage points higher for hospital births than home births.  (6.4 percent vs 12.9 percent).  This reflects complications occurred almost twice as often.
• There was a statistically significant better rate of outcomes in home birth for NICU admittance, assisted ventilation required for more than 6 hours, intolerance of labor and meconium staining amniotic fluid.  For all other outcomes there was not a statistically significant difference between the two. 
• The rate of adverse outcomes for the mother were approximately 8 percentage points higher for hospital births than home births (2 percent vs 9.9 percent).  This reflects complications occurred more than 5 times as often.
• There was a statistically significant better rate of outcomes for home birth among 3rd and 4th degree perineal lacerations and initial cesareans.  The differences between all other categories were not considered statistically significant.  
• The rate of home births that transferred to a hospital was about 5.7 percent.  This includes mother's or baby's being transferred after the baby was born.  I initially published this with a lower number (3.6 percent), but that only counted transfers that occurred before the baby was born.  Thank you Annie for suggesting this number was too low.

Natural childbirth advocates claim that interventions cause many of the complications in hospital births.  I compared home birth to hospital birth where the labor was not induced, augmented, or made use of an epidural.  The data otherwise is the same as above.

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Click here to view all data including confidence intervals

• The rate of adverse outcomes for the baby were approximately 1.3 percentage points higher for hospital births than home births.  (6.4 percent vs 7.7 percent).  
• More babies received assisted ventilation immediately after being born at home than at the hospital (1.4 percent vs 2.8 percent).  This reflects that this happened almost twice as often at home than at the hospital.  
• More babies did not tolerate labor so that in-utero resuscitation measures, further fetal assessment or operative delivery at home than at the hospital.  (.29 vs 1.3).  This reflects that this happened about 5 times as often at the hospital than at home.
• There was less staining of amniotic fluid with meconium among babies birthed at home than at a hospital. (1.7 percent vs 3.4 percent).
• The rate of adverse outcomes for mother were approximately 1.7 percentage points higher for hospital births than home births. (5.5 percent vs 1.9 percent).  This reflects that complications occurred almost twice as often at the hospital than at home.
• The rates were better for home birth for 3rd and 4th degree perineal tears.
• The rate of initial cesarean was approximately 3 percentage points higher for intervention free hospital birth than home birth. (1.3 percent vs 4.3 percent).  This reflects that cesareans occurred almost three times more often among hospital births than home births.

Sometimes people will allow that home births are safer in the less serious outcomes, but when something bad happens your baby is more likely to die if you are at home.  Unfortunately the statistics regarding deaths are somewhat unreliable.

There are two fields used to describe mortality.  One is a link with infant death records.  This records that a baby died sometime in the first year, however the cause of death could be completely unrelated to its birth.  Another field that is used is whether the baby was alive when the birth certificate data was recorded.  There was a note about data quality saying that before 2005 there were records that said the baby was not alive, but there was no death certificate that matched the record.  It said this number was corrected after 2004, however there were many records after 2004 that said the baby was not alive, but it did not also have the field that linked the death certificates marked.  The majority of these records that had the discrepancy did not have any corresponding birth complications associated with them (ie resuscitation, NICU stay, etc) so I am assuming these records were probably marked incorrectly and thus this field isn't meaningful.

The second measurement of mortality are baby's who are not born alive otherwise known as still born.  These records are stored in a different database because the babies do not have a birth certificate.

In an effort to be unbiased I provided a few different rates for comparison.

Click to enlarge

• The differences in mortality rates between home birth and hospital birth were not significant.
• Using the most accurate data in the defined parameters (full term birth, born at home, on purpose, with a trained attendant vs low risk hospital birth) the actual outcomes were more favorable for home birth.
• I included rates for home births of unknown planning with unknown attendants for curiosities sake and allowed babies from 36 wks gestation as well.  Even these were either only slightly worse, or better than the hospital births rates.
• The "Not Alive When Reported" rate was poorer for home birth, by quite a bit, but as I mentioned earlier, this field is extremely questionable in its accuracy.  

DISCUSSION

Is birth safe?
Yes, but not really.  The best rates above have around a 5 percent chance of something wrong happening.  That doesn't sound like a lot, but when you phrase it as a 1 in 20 chance.  It would mean that 5 out of your 100 female/mommy Facebook friends would have had some less-than-ideal birth experience (unfortunately I was one of those five)--not rare and unheard of.  Also those optimum rates were for low risk pregnancies.  There is a high percentage of pregnancies that aren't low risk, so overall the rates might be (really I have no clue) more like 10 percent (1 in 10) to 15 percent (1 in 6ish).  Thankfully, with modern medicine, the vast majority of the time the less-than-ideal outcome doesn't last more than a few weeks (perhaps which is why there doesn't seem to be much effort in trying to improve it?).


Is home birth safe?
Yes, in Washington state, it has been safer than hospital birth for low risk pregnancies.

Does this mean home birth is always safer?

Probably not.  It is illegal for midwives to deliver babies at home in many states, or it is illegal for them to carry medications or administer antibiotics.  If proper backup is not available it is likely the results would not be so favorable.  This analysis is also for women who have low risk pregnancies, the outcomes could be different for higher risk pregnancies.

Should all women have access to home birth?
Yes! and no.  I think this data shows that it is safe, under prudent conditions.  All women in the U.S. who are deemed low risk should have high quality home birth care available (ie it shouldn't be illegal).

Do excessive interventions make hospital birth less safe?
Probably.  This particular analysis starts to make a case.  I may analyze this in future posts (I do have a post on epidurals almost completed already), but unfortunately there is not a whole lot of description on why an induction, augmentation or epidural was used so it makes it difficult to definitively say what came first--the intervention or the complication.  The fact that intervention free hospital birth has better outcomes than overall hospital birth alone isn't really indicative, but when combined with the information that a self-chosen group of women, who choose an intervention free birth beforehand (ie a home birth), have similar results provides stronger evidence toward the claim.

What's up with the assisted ventilation immediately after birth?
That was the one adverse event in which happened more often at home (albeit still only 3 percent of the time), than at a hospital.

Information lacking in the data
A neonatal mortality number (baby dies in the first couple months of life) is missing from this data.  This is a number that opponents of home birth commonly use to reflect that home birth is not safe and the fact that it is missing is unfortunate.  The inaccurate Not Alive When Reported number or the too broad infant mortality numbers are the closest we get.  Mother mortality is another number that is missing from the data.

Me/my wife/my baby would have died if I wasn't at a hospital
Yeah, me too.  The distinction that many people do not realize is that having a home birth does not mean the hospital isn't available.  The fact that it is available is what makes home birth safe.   Also, as shown above, the life threatening event is less likely (but not completely unlikely) to occur when you are at home.  Was the emergency caused by bad luck, or due to a bad drug interaction?

For some people the small chance that something really bad will happen, and being in the place it can get treated the quickest, is a more important a factor in deciding where to birth.  For others reducing the more common, though less serious, adverse outcomes is more important.  I believe that the important thing is that every women has the opportunity to receive quality care that aligns with her own risk comfort level.

Freestanding birth centers
I didn't include birth center births because some hospital's attached birth centers got labeled as free standing birth centers.  I didn't feel like picking through them and figure out which were truly free-standing and which were not so I chose to not include them.

What I would like to see
Home birth be legal, regulated, and covered by insurance in all fifty states.  I also think it would be great if CNM's and doctors delivered at home.  There are other things too, but I think they are out of the scope of this post.


Bias
I tried to be unbiased and get a true look at the safety of home birth.  I attempted to address concerns regarding perinatal mortality versus infant mortality.  I tried to include prudent parameters for home birth (ie full-term gestation and with a midwife attending) and only comparing similar demographics in the hospital.  Thus comparing home birth to only very low-risk pregnancies and intervention free births.  I hope that neither side can look at this and say I purposely skewed the data one way or the other.

Soap Box
If a woman decides to have a home birth or a natural birth she is not putting the "experience" ahead of her or her child's safety.  She should not be made fun of (cliche joke on TV), or told that she won't get a medal for doing it natural.  I know birth is tough.  I know home birth and unmedicated birth are not for everyone, nor am I saying that they should be, but women who look at this data and think it is worth it, should not be told they are crazy or that they are putting their child's life in danger, or every other awful  thing people and providers may say.

METHOD

This data comes from the Washington State birth certificate database for the years 2002 - 2007.  Here is a bit more information about me and the data.

• Confidence Intervals were calculated using this document.  I used Poisson distributions when the number of events was less than 20 (I may have neglected this step, due to laziness, in cases where it was obviously not going to be significant).  It said to use 3 events if 0 events occurred, but this gave me weird results where the CI was statistically significantly higher than the comparative CI when in actuality there were no events recorded.  I switched to using 1 for the high, and zero for the low, and got more meaningful results.  I used the simplistic method in comparing confidence intervals, where statistical significance is only true when the intervals do not overlap.
• Results were extracted using SQL.  They were copied into Excel where standard errors and confidence intervals were calculated and compared.
• Each birth was only counted once, if multiple adverse reactions occurred the most severe event was the one recorded (ie if a baby had seizures, NICU stay and then died :(. The seizure and NICU fields would not reflect those events).
• The adverse reactions recorded for the baby were:
• adverse - a sum of all the events below
• death - This does not include still births, but includes any baby that died within the first year of its life.  Whether the death was related to the birth or not is not specified.
• assist_vent - Assisted Ventilation Required Immediately Following Delivery
• assist_vent_cont - Assisted Ventilation Required for More Than 6 Hours
• NICU - NICU Admission
• surfactant - Newborn Given Surfactant  Replacement Therapy
• sepsis - Antibiotics received by the Newborn for Suspected Neonatal Sepsis
• seizure - Seizure or Serious Neurologic Dysfunction
• birth_injury - Significant Birth Injury
• intolerance_of_labor - Fetal Intolerance of Labor such that One or More of the Following Actions was Taken:  In-utero Resuscitation Measures, Further Fetal Assessment, or Operative Delivery 
• meconium - Moderate/Heavy Meconium Staining of the Amniotic Fluid
• The adverse reactions recorded for the mother were:
• maternal_adverse - a sum of all the events below
• transfusion - Maternal Transfusion
• tear - Third or Fourth Degree Perineal Laceration
• rupture_uterus - Ruptured Uterus
• hysterectomy - Unplanned Hysterectomy
• ICU - Admission to Intensive Care Unit
• operation - Unplanned Operating Room Procedure Following Delivery
• initial_cesarean - the birth was via cesarean and the mother had not had a previous cesarean
• transfer_to_hospital - the mother did not give birth at home, though she intended to.\
• I could not compare the number of still born babies between home births and intervention free hospital births because the fetal death records do not specify what interventions occurred.

Please let me know if you find any errors, mathematical or otherwise.  I hope this information is helpful and meaningful.  I spent an excessive amount of time producing this so pats on the back are appreciated. :)  Joining Kachingle is a great idea too!

Recommended reading and resources on natural childbirth:

Complications Associated With Fetal Macrosomia

This is part five in my Pregnancy and Birth Outcomes Analysis based on the Washington State birth certificate data.  This is my final post exploring fetal macrosomia. Sorry it has taken so long to get it written, but I just kept getting sucked into a whole bunch of different ways to analyze the data, and spent a lot of time making sure that the data was correct plus, you know, taking care of my kids, starting a vegetable garden, and training for a half marathon.

Edited To Add:  I reorganized the post to start with the conclusion, followed by the results, then the method as internet surfers usually will click away if the important stuff isn't immediately viewable.

Conclusion

Having a large baby does slightly increase your chance of having complications especially having an initial cesarean.  The two biggest indicators that I could find for having a large baby were having diabetes, and carrying the baby at least a full 40 weeks.  Gaining a lot of weight during pregnancy, having gestational diabetes, or having a lot of extra weight before getting pregnant did seem to increase your chances of having a bigger baby, but only by a few ounces.  

Common methods to try and prevent a big baby is restricting a mother's food intake and inducing labor.  I think the evidence here tends to argue against restricting what the mother eats.  The stress and emotional and physical frustration this causes is not worth shaving a few ounces off the baby's weight.  

In general induction carries its own risk.  I know this from analysis that I have not yet posted.  In this specific case baby's born from a labor that was induced did suffer more complications, even than babies who were born 42+ weeks, but because this sample size was small it was mostly not statistically significant¹.     

In this specific case there also was no statistically significant difference in the rate of initial cesareans between women whose labors were induced or not.  In other words a woman who was induced at 39 weeks was just as likely to have a cesarean as a woman who went into labor spontaneously at 39 weeks and being induced at 39 weeks did not make you more or less likely to have a cesarean than a woman who went into labor spontaneously at 41 weeks (basically the confidence intervals were large at every gestational age for both the induced and not induced groups that it really didn't provide any useful information). So in this case I would say that the evidence does not argue for or against the increased safety (both baby's and mother's) in inducing labor on the sole basis of the baby potentially being "big".   

In general I would say this validates my general opinion of let nature take it's course, and listen to your body and provide it with what it says it needs.  If you do end up having a big baby and there are complications, there wasn't a whole lot you could do to prevent it.  It is what it is.  If you are diabetic you should strive to maintain your blood sugar, which I'm sure you already do, not only for your baby's potential size, but because there are other potential complications due to diabetes.

Results:

Analyzing Complications Related to Fetal Macrosomia

(Click to make larger)

Raw Data

• There are increasing complications in all categories except the death of the baby associated with big babies.  
• The rate of cesarean birth was 9.2 percent higher among large babies (roughly 1 in 4 vs 1 in 6).  

Lauren at HoboMama wondered about scheduled ceseareans, and I also wondered about inductions so I calculated some further figures.

• 13.3% of the time women with large babies had their first cesearean, without a trial of labor compared to 8.8% of women with babies less than 4200g.  So of the 9 percentage point increase roughly 5 of those percentage points were from scheduled cesareans.
• 27% of the time women with large babies had their labor induced versus about 22.4% of women with babies less than 4200g.  So there was an increase of about 4.6 percentage points in inductions.  But the increased rates in complications for bigger babies compared to smaller babies remained almost exactly the same even when the mother's labor was not induced. 

Method:

Click here to see information about the data.

• I calculated the average weight for babies in Washington and then calculated what weight range would fall above the 90th percentile.  I had the understanding that this was the definition for fetal macrosomia, till I went back and looked at the wikipedia article that qualified 90th percentile for gestational age.  Oops forgot that last little tidbit.  But I don't want to go back and do the calculations so I'll just stick with babies who are in the 90th percentile for full term babies (37 weeks or more gestation).  I could have used the entire population.  The average weight was less (7.45lbs vs 7.6lbs), but because there is more variance in size, the 90th percentile calculation was actually higher (9.4bs vs 9.3).  I rounded the 9.3lbs to 4220 grams and called it good.  
• I grouped babies into the above 4220 grams, and 4220 grams and below, and both groups the babies had to be full term (though I accidentally forgot this stipulation at first, and it did not change the results by much)
• I calculated the rate of occurrence for various groups of complications:
• Adverse Baby
• Assisted Ventilation Required Immediately Following Delivery
• Assisted Ventilation Required for More Than 6 Hours
• NICU Admission
• Newborn Given Surfactant  Replacement Therapy
• Antibiotics received by the Newborn for Suspected Neonatal Sepsis
• Seizure or Serious Neurologic Dysfunction
• Significant Birth Injury
• Moderate/Heavy Meconium Staining of the Amniotic Fluid
• Fetal Intolerance of Labor such that One or More of the Following Actions was Taken:  In-utero Resuscitation Measures, Further Fetal Assessment, or Operative Delivery
• Adverse Mother
• Maternal Transfusion
• Third or Fourth Degree Perineal Laceration
• Ruptured Uterus
• Unplanned Hysterectomy
• Admission to Intensive Care Unit
• Unplanned Operating Room Procedure Following Delivery
• Initial Cesarean
• The mother had her first cesarean.  I didn't include repeat ceseareans because many times they would have happened regardless of whether the baby was big or not (due to not many hospitals allowing VBAC's).  
• Death of the baby
• This one is a difficult statistic (both emotionally :( and as far as how accurate it is) as it is a field that was calculated by the WDHS where they took the infant (1 yr and under) death certificates and tied it to the birth certificates.  Thus the death of the baby may be totally unrelated to its birth. I also added baby's that were stillborn to this statistic.
• I calculated the confidence intervals in the same manner as this post.
• Due to the rarity of the events I calculated the confidence intervals for the death of a baby using a Poisson-Distribution via the tables in Appendix 2 of this document.

Future Posts:  I think the next topics I am going to tackle will be epidurals, augmentation and induction.  But I might wait a bit first and give myself a break.

Foot Notes:
1- If you compared rates of complications per weeks gestation most of the confidence intervals overlapped but they didn't at 39 weeks and 41 weeks, in those weeks not inducing had less complications and it was statistically significant.  I am not posting the graphs of these results because I think induction needs its own post and I get off on too many tangents

Baby Birth Weight and Mother's Pre-pregnancy Weight

This is part four  in my Pregnancy and Birth Outcomes Analysis and continues to explore fetal macrosomia.

 Pre-pregnancy Weight vs Baby's Birth Weight

Conclusion:

It does not seem that a mother's pre-pregnancy weight is a huge factor in determining how much their baby will weigh, except in the case of women who are considered underweight, their babies do tend to be a bit smaller.  

Results

• There seems to be a statistically significant trend in a mother's pre-pregnancy weight and the birth weight of her baby, however the confidence intervals do start to overlap above 200lbs.  
• The steepest increase in average baby weight is seen in the 90-140lb range after that the increase is very small (the average baby weight increases by approximately .5-1oz for every 20lb group).  

Mother's Pre-pregnancy BMI vs Baby's Birth Weight

• This is similar to the above analysis.  Each mother was put into a group based on her pre-pregnancy BMI (Body Mass Index), which is a height to weight ratio, that some health professionals use.  I used the common groupings of: 
• Less than 18.5 (underweight), 
• 18.5 - 24.9 (normal), 25-29.9 (overweight). 
• Commonly 29.9+ (obese) is all lumped together, but I decided to further categorize it and added 29.9 - 39.9 
• 40 - 49.9 
• 50 - 59.9 
• Over that the sample size was too small and the confidence intervals too large.

• A baby's birth weight is higher for women who had a higher pre-pregnancy BMI.  It is statistically significant till you get a BMI over 40.
• The greatest difference  (5.6oz) is found among baby's born to mother's whose BMI is considered underweight compared to mother's whose BMI is considered normal.

Method:

See here to see information about the data.

• The mother's are grouped by their pre-pregnancy weight in 20lb increments (starting at 90-110lbs, ending at 320-340lbs).  The average baby weigh (in pounds) is calculated for each group.  For the groups of mother's weighing more than 340lbs the confidence intervals were wide due to the small sample size.
• The data is to full-term babies (at least 37 weeks)
• The confidence intervals were calculated in the same manner as this post.

I'm going to wrap up the exploration in fetal macrosomia by comparing the rates of complications of baby's who are large versus babies who aren't.  

Relationship Between Baby's Birth Weight and Diabetes

This is part 3 in my Pregnancy and Birth Outcomes Analysis and continues to explore potential relationships of fetal macrosomia.

Comparing Average Fetal Weights for Women With Diabetes, Gestational Diabetes and No Diabetes

Conclusion

 It seems that either women who have gestational diabetes are doing a great job controlling it, or that gestational diabetes does not affect baby birth weight by that much.  However having diabetes pre-pregnancy does seem to influence the baby's birth weight quite a bit more. 

Results:

• There was an approximate 1.5oz difference in weight between babies whose mothers had GD versus those whose mother's did not have diabetes.
• There was an approximate 4.6oz difference in weight between babies whose mothers had diabetes before they got pregnant versus those whose mother's did not have diabetes.
• There was an approximate 3.2oz difference in weight between babies whose mothers had GD versus babies whose mother's had diabetes before they got pregnant.
• The confidence intervals do not overlap so the differences are statistically significant.

Method:

See here to see information about the data.

• I used sql server to calculate an average baby weights for women who's baby's were full-term (37 weeks or later and were put in the following groups

• Had diabetes before they got pregnant (did not distinguish between Type 1 or Type 2)
• Diagnosed with Gestational Diabetes
• Did not have diabetes

• The confidence intervals were calculated in the same manner as this post.

Baby Birth Weight versus Gestation

I got some positive responses so I'll keep posting my analysis of the birth data.  So this is part 2 in my Pregnancy and Birth Outcomes Analysis and further explores possible relationships between various variables and fetal macrosomia.

See here to see information about the data.  

Method:

• Calculated the average birth weights for full term baby's born grouped by how long their gestation period was.
• Confidence intervals were calculated in the same manner as this post.

Results:

Comparing Average Baby Birth Weights 
to Their Gestation Time

• The confidence intervals did not overlap except for babies born at 43 weeks (there were only 117).  
• It is not statistically significant that babies born at 43 on average weighed less.  
• The increase in difference in average weight is not linear.  

Conclusion

I thought these results were really interesting.  I'm not sure if you can really use this information to determine fetal growth, but knowing the uncertainty involved in estimating weight via ultra-sound I can't think of a better way to estimate fetal growth than this, so I'm going to go with it.

I had the understanding that a baby gained about half a pound per week the last month of pregnancy.  I'm not sure where I heard this.  I read a lot, so it must have been somewhere, but it doesn't seem to be true.  The average weight gain is just less than 6oz (so just less than 1/3lb per week) per week from 36 - 40 weeks, and it isn't a linear gain, meaning it isn't the same amount of weight each week.  Their growth rate seems to slow the longer they gestate.  I was pregnant with my second child four weeks longer than with my first and as every week passed by I remember thinking that my baby just gained 1/2lb and despite trying not to be, I was a bit concerned. My second ended up being just 3/4lb heavier than my first.  This information would have been nice to know.

It seems like there could be contradictory conclusions about this data in regards to whether inducing labor is okay.  On one hand you could say, well the baby isn't going to grow that much more anyway, so you might as well induce early (for convenience), on the other hand you could say the baby isn't going to grow that much more, so you might as well let them stay till labor happens spontaneously (to contradict the "big baby" argument).   I agree with the latter conclusion, because I believe that there is other important development that happens at the end that happens better in-utero.

Edited To Add:  There is quite a large difference between 39 weeks and 41 weeks (11oz), so I guess there may be some basis to assume that waiting could result in a much larger baby.  But there is always the unknown of how much longer it will be before labor starts on its own... 

* Please leave me comments if you found this interesting.

Does a Baby's Birth Weight Correspond With A Mother's Weight Gain?

This is part one on a series of pregnancy and birth outcomes.

I've been messing around with the birth certificate data, but hadn't formally prepared anything to be posted because honestly that is the least fun part.  But Lauren at Hobomama (great blog!) had a post about her midwife harping on weight and she questioned whether a mother's weight gain really influences the weight of their baby.  So I thought, "Hmmm lets see".  Here are the results:

Conclusion

On average, the more weight a mother gains, the more her baby will weigh.  However, the average difference in a baby's weight, between a mother who gains 25lbs versus a mother who gains 70lbs, is only 1/2 lb.  There seems to be more involved in fetal macrosomia than a mother's weight gain.  If you feel comfortable that you eating nutritiously and are being as physically active as you can, then you are probably fine. If a provider tells you to eat less to avoid having a huge baby, this statement is based on exaggerated evidence at best.

Results:

Click to make larger

• You can see that in general as a mother gains weight her baby on average is larger. The exception is when weight loss occurs or only 0-9lbs of weight gain, however the confidence intervals overlap in this range so it is not statistically significant.
• The results are significant till you get to fifty pounds and over, or when the mother lost weight then the results become less relevant.  
• Babies born from women who gain the recommended 20-29lbs weight on average 7.51bs (7lbs 8oz).  
• Babies born from women who gain 30-39lbs weigh on average 7.66lbs (7lbs 10oz).  The 2oz difference is statistically significant.  
• Babies born from women who gain 40-49lbs weighed on average 7.82lbs (7lbs 13oz).  The 3oz difference is statistically significant.

Just for curiosity sake here is the entire chart in a mostly full range of weight gain and loss.

• It seems that baby weights rise when women lose a lot of weight, but the confidence intervals for this are large and thus the information isn't really meaningful.  

Method:

• I summarized the data of all women from 2003 - 2007 who carried their babies full term (37 weeks), whose starting and delivery weights were provided and seemed reasonable (above 90lbs).  I did not use the weight gain field calculated by the WSDH because it did not include mother's who lost weight.
• I excluded data when the weight gain was above 79lbs or whose weight loss was below 9lbs because the results were not statistically significant. 
• I grouped all women in 10lbs ranges so 0-9, 10-19, 20-29, etc and calculated the average weight of their babies in grams, and converted it to pounds by multiplying the weight by .0022.
• I used sql server's stdev function to calculate the standard deviation for each group.  To calculate the confidence interval I used the instructions from here and summarized as:
• CI is the confidence interval
• avg - is the average baby weight
• SD - standard deviation
• N - number of mothers in the sample

• I graphed the results in Excel.  I included both the confidence intervals and the actual results.  To determine statistical significance I use the simplistic logic that if the confidence intervals overlap then the results are not statistically significant, if they don't overlap, then they are.  This logic is per the recommendations from the Washington State Department of Health.

Future Posts

• Rates of fetal macrosomia compared to mother's weight gain or loss
• Rates of fetal macrosomia compared to mother's initial weight or bmi
• Fetal weight and fetal macrosomia compared to whether a mother has gestational diabetes or not.

These posts take a long time to write up, so I'll get to them when I can.  Please leave me a comment if you find this information useful or interesting so I know if it is worth my time and effort to write up my analysis. 

Pregnancy and Birth Outcomes

A couple years ago I requested all the birth certificate data from the Washington State Department of Health.  ETA:  Here is a link to the form that providers fill out after a baby is born. I am geeky and like databases.  I like researching pregnancy and birth and I wanted to see if I could get some more interesting results than the ones they post on their website.   At the time it was very simple.  I signed a paper saying I wouldn't give the actual data to anyone else and a CD came in the mail very quickly.  Granted the data was not in a format that was user friendly at all, but I got the data easily.  Now however is a different story. I asked for an update that included the 2008 and 2009 data, and the infant death data as well, and I am told that they are now charging $30 a file.  (I would have been charged $420 for the data I had previously received).  I am now thinking this is illegal because there was an article in the Seattle Times saying that they are trying to get legislation (but haven't yet) to allow them to charge because "civic gadflys" are wasting taxpayer money.  How rude.  I am not a gadfly.  On one hand I want to make a fuss on the principle of the matter, plus the freedom of information act is important, on the other hand maybe it really does take them a long time to get the data rounded up and they really are overwhelmed.

My plan is to do a series on this blog based on the resulting analysis.

METHOD:

I've taken the data from 2002 - 2007 (I have 2000 and 2001 as well, but the information collected changed in 2002 so its easier for me just to ignore the earlier data instead of trying to combine it somehow) and wrote a script to parse the fixed width delimited data and input it into a SQL Server database.

I've also written a script that allows me to execute a SQL query and import the results into Excel and create a chart of the data.  I have to admit I feel pretty studly that I have been able to do this.  I find it much easier to interpret the data visually and this makes it a lot easier to do.

I'm doing my best to be careful, accurate and use statistically sound analysis.  However I have no one checking my work.  If you find any errors PLEASE let me know.  

MY RESUME AND BACKGROUND:

Most often when "studies" like this are done they are either done in a university setting, or are research funded by some interest group.  I belong to neither.  I have a B.S. in Computer Science and a minor in Math with a year of that being in statistics.  I've often thought that if I weren't a computer programmer I'd love to be a statistician, however it was quite a while ago since I've done any statistical analysis, so I'm doing my best.  I am currently unemployed and my primary responsibility is raising my children.   I was formerly employed at small company that makes exercise software for physical therapists.  

Besides being nerdy and enjoying analyzing data I have an interest in childbirth and pregnancy.  I believe in "evidence based" medical care and am an advocate for unmedicated birth, the midwife model of care, birth centers, and home births.  My first child was born at a birth center and I delivered her without medication.  My second child was supposed to be the same, but I ended up transferring to a hospital where she was born via cesarean.  My experiences made me wonder exactly what the rates of complications are for various situations, and are the risks and/or benefits exaggerated in the debate on what the best prenatal care consists of.  My goal is to provide some hard numbers that give women some more information so that they can do a risk/benefit analysis on the type of care they receive and their decisions regarding labor.  There is a lot of useful information in the birth certificate data, but there is also a lot of missing information that would make analysis better.  Some day I hope to create my own "ultimate birth survey" but till then, this will have to suffice.  

All posts in this series

Part 1 - Mother's Weight Gain Compared to Baby's Birth Weight
Part 2 - Baby's Birth Weight Versus Gestation
Part 3 - Baby's Birth Weight and Diabetes
Part 4 - Complications Associated With Fetal Macrosomia
Is Home Birth Safe?