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If my baby measures big, do I have to have a C-section?
Q: When I went in for my last ultrasound, my doctor told me that my baby was very large. Does this mean I will have a difficult pregnancy or have to have a Caesarean?
Crystal Concorde
A: Without knowing the specifics of your pregnancy, I am happy to offer some general comments about having a large baby.

If you could weigh all babies during each week of pregnancy, you’d see that they come in a range of sizes. Doctors use the term “large for gestational age” (LGA) to descote the 10 percent of babies with the highest weights for each week of pregnancy. We say that these babies are greater than the 90th percentile for their gestational age. At term, the average baby weighs around 7 pounds. About 10 percent of babies weigh more than 8 pounds 13 ounces.

Some babies are large simply because they inherited the genes from their parents. Large babies may also result from excessive maternal weight gain during pregnancy, usually the consequence of a high-calorie diet. Another cause of LGA babies is maternal diabetes. Women with diabetes have higher levels of sugar in their blood circulation. Babies exposed over weeks to the extra sugar grow larger and accumulate extra body fat.

Larger babies may cause more difficult labors, particular for women who do not have a spacious pelvic bone region. Labors may be prolonged, vaginal births may be more difficult and Caesarean sections may be necessary. Additional concerns exist for babies of diabetic mothers; they may have breathing difficulties if they are born before 38 weeks gestation, and they are at risk for low blood sugar (hypoglycemia) following delivery.

If your baby appears to be large during pregnancy, your doctor will first review your gestational age. (Some babies measure large because of a miscalculation in dates.) Your doctor may also assess your medical history and diet. You will likely be offered a glucose screening to see if you have undetected gestational diabetes. You may wish to meet with a dietician to plan for an optimal diet over the rest of your pregnancy.

At the end of your pregnancy, if your baby appears to be over the 90th percentile and your cervix seems ready for delivery, your doctor may suggest inducing labor. Inductions are offered to maximize chances for a vaginal delivery, and to avoid unnecessary Caesarean sections.

Keep in mind, ultrasounds can overestimate or underestimate fetal size. This is especially true at the end of pregnancy, and doctors may be unable to predict who will have a successful vaginal delivery and who will need a Caesarean section. For this reason, doctors usually advise that you attempt a vaginal delivery rather than recommending a Caesarean section without labor.

Laura E. Stachel M.D. Obstetrician & Gynecologist