The Baby is Big. I'm Only 2 Weeks From My Due Date. Why Won't My Ob/Gyn Induce Me This Week?
I AM 2 WEEKS FROM MY DUE DATE WITH MY FIRST BABY AND THE ULTRASOUND SAID THAT MY BABY WEIGHS ALMOST 9 POUNDS. WHY WOULD MY BABY BE SO BIG AND IS THIS ACCURATE? IF WE KNOW THE BABY IS GETTING SO BIG WHY WON’T MY DOCTOR INDUCE ME THIS WEEK?
There are many factors that go into how big a baby is. Were you a big baby when you were born? Very often if you were large at birth there are genetic factors that influence the size of your baby and you may make a big baby as well. How much weight have you gained in the pregnancy?
We encourage women of average weight to gain between 25 and 35 pounds in pregnancy. Women who gain significantly more weight can make a bigger baby. Did you have gestational diabetes in pregnancy, and if you did was it well controlled? Women with gestational diabetes in pregnancy, especially those whose blood sugars are not in good control can have large for gestational age babies as well.
Sonographic estimate of fetal weight can be off by 15 percent in either direction (smaller or larger). Even though ultrasound is very good at estimating fetal weight, it certainly has its limitations. I have seen estimates of fetal weight in the 10 pound range, where upon delivery the baby is 8 pounds, whereas in other instances the estimation of fetal weight by ultrasound is within ounces ounces of the true birth weight.
Doctors evaluate estimations of fetal weight clinically by using Leopold maneuvers. We use our hands to evaluate the estimation of fetal weight by experience. Again, like with ultrasound there are times we are spot on, and there are times where we can be off by over a pound. There was a study done in women having their second baby where they looked at sonographic estimate of fetal weight, physician’s estimate of fetal weight, and mothers’ estimate of fetal weight (knowing what her prior baby weighed), and the mother was the closest. Needless to say, estimation of fetal weight by any means is not a perfect science.
Macrosomia is a term that obstetricians use to describe babies with a birth weight of greater than 4500 grams (10 pounds).
Impending macrosomia is when we see that the baby is approaching that number yet the patient is not in labor. It seems intuitive that we would want to try to bring labor on early in those patients who appear to have impending macrosomia, but there are two reasons why we don't do this.
Number one, unless there is maternal or fetal jeopardy, we do not bring on labor before 39 weeks of gestation (a full 7 days before the due date) because there is a small chance that the baby’s lungs are not fully developed yet (this maturity is different from baby to baby) and therefore we can be doing more harm than good and we would not want to prematurely force the hand of nature.
In addition, induction of labor doubles the risk of cesarean section. This would clearly be warranted if there was a situation of maternal or fetal jeopardy, but would not be warranted for impending macrosomia alone. Numerous studies show that there is actually a higher rate of vaginal delivery by letting nature take its course and allowing these bigger babies to go into labor as opposed to inducing them, even if it means that the baby will be larger.
Babies that are forced into labor with induction can come into the pelvis in more abnormal positions that can increase the risk of cesarean section, and Macrosomic babies are more at risk for an obstetrical emergency called shoulder dystocia. This happens when the anterior shoulder of the baby gets stuck behind the mother’s pubic bone. This can lead to fetal injury or death, and maternal injury as well. The risk of shoulder dystocia can be increased by inducing and forcing labor on a known Macrosomic baby.
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