Sunday, March 27, 2011

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.


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.


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. 

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


Momma Jorje said...

We love your hobby! Thanks for sharing all this data. With GD, I let / asked my doc to strip my membranes (twice) to induce labor. (I figured at least it was more natural than pitocin.)

Next time, I'll try to just hang in there. Doc was nervous because I have a history of large babies, but I don't think they were THAT big.

Do you have any plans to take race into consideration? I am part Choctaw and I've been told that Indians have big babies.

Laura said...

Momma Jorje- The average weight for native american babies (either mom or dad) was 7lbs 6oz and for non- Native Americans the average weight was 7lbs 7oz. So I guess not.

ilse said...

Thank you so much for this info, im currently 31 weeks pregnant with my second baby my first was born at 42 weeks weighing 5.2kg or 11 pound 8 oz, i havent had GD with either preganacy. Im Dutch living in New Zealand and my midwife seems very relaxed even though my fundal measurements are 5-6 weeks ahead and everything indicates to another large baby, im very worried should i try go into labour naturally only to have a emergancy C section like last time? or book a C section? im extremely low in iron even though im taking pills twice a day and eating red meat daily and my ribs back and pelivs hurt constantly
what should i do?

Laura said...

ilse - congratulations on your pregnancy! I'm sorry you are worried about your baby's size. It is so hard to say what you should or shouldn't do, but I would try to worry less. I know that is hard, but really there is only so much you can control. Whatever happens, or whatever you decide, will probably workout just fine--the odds are with you. :)