One of the biggest challenges I face as an Obstetrician is determining how to handle big babies. Currently 10% of women deliver babies that weigh more than 4000 g (8lbs 13oz), which is the medical definition of ‘big’ (macrosomia). For first time moms especially, this can be a dilemma. If you await labor, the baby continues to grow even bigger during that interval. The bigger the baby, the more likely the need for cesarean section. Alternately, induction can often subject the patient to a prolonged labor that may end in cesarean section regardless. Despite delivering babies for over 10 years, I can’t always accurately predict whether the baby will fit through the mom’s pelvis. Until I can invent the Magic 8 Ball of labor, I will have to rely on studies and clinical judgement.
Some situations are straightforward, if the baby is actually a toddler (>11lbs), then the recommendation is to perform a cesarean section. Period. The big debate lies in how to manage those pregnancies with babies between 9-11 pounds. The current recommendation is to wait for these women to go into labor on their own. Statistically, induction increases the risk of cesarean, so the thought has always been to let nature take its course.
The current recommendations are based on studies looking at induction versus spontaneous labor. But that is not really a fair comparison. When I see a woman at 39 week who has a suspected 9 pound baby, my choices aren’t really induction versus spontaneous labor. If they were, I would obviously choose spontaneously labor. But I can’t just wave my magic wand and make contractions appear out of thin air. In first time moms spontaneous labor is almost always better than induction. My actual choice is between induction or waiting for labor to occur. Labor can be elusive, it might not occur for several more weeks.
A recent large study has finally looked at this issue. Cheng et al (BJOG 2012;1119:402-409) looked at 130,000 labors of first time moms with big babies. They found that induction at 39 weeks actually lowered the cesarean section rate. The rate for women who were induced was 35% versus 41% for those who awaited labor to occur. One of the key statistics was that in the wait and see group, 30% did not go into labor by 41 weeks. I told you labor can be elusive.
This study is not perfect. It does not take into account the patient’s BMI or cervical dilation, which we know to effect the success of induction. Additionally, the best tool we have for estimating baby size is ultrasound which can often overestimate the size of the baby by up to 10%.
Honestly I was surprised by this study. I have always been more of the wait and see type. Is induction the right choice for all women with big babies? Of course not. Each woman’s pregnancy and labor is unique. Therefore, I do not think this study should cause women to decide if induction is right for them. As always, we encourage you to discuss your options and your unique case with your provider.
Did you give birth to a big baby? If so, were you induced or did you wait to go into labor?
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