If You're Worried Your Baby Will Be Too Big To Deliver, Here's What Science Says

by Cat Bowen

When I first got pregnant, I was terrified. My whole life I'd been told just what a chunker my brother was when he was born. My mom joked that he "ripped her a new one," and I'm not going to lie, I definitely worried my kids would take after him. When my mother-in-law told me that my husband was a huge baby with a gigantic head? I had palpitations. I talked to my OB-GYN and asked her, "Will my baby be too big to deliver?" She just chuckled at me and told me to ask again when I was through my first trimester. But how do doctors make this determination?

The worry over how you will deliver, and the relative safety of it, is something every mom who's given birth can relate to. Many moms go into labor and delivery with one idea in their head of how it will all play out, only to realize that it isn't going to happen that way. It can be devastating. According to The Mayo Clinic, one of the chief reasons that babies are ultimately delivered via C-section in lieu of a vaginal birth is because they were estimated to be large for their gestational age (LGA). While there are many possible causes for babies to grow so big, heredity seems to play an outsized role in the size of baby at delivery. That means if you or your partner were LGA, you're more likely to deliver a baby who is also LGA.

According to the University of Rochester Medical Center, there are myriad reasons why your baby might grow to be LGA. As I mentioned, heredity is the primary cause for babies born large, and possibly too big to deliver vaginally, but also, researchers noted that it can happen when a mother gains too much weight during her pregnancy, which has a corollary response in the fetus. They noted as well that mothers who are diagnosed with gestational diabetes are prone to babies that measure LGA because the elevated blood sugar levels associated with the condition can result in a baby getting more calories than what is otherwise considered normal. The other cause of a big baby is plain old dumb luck. My mother was not a big baby, nor were any of the rest of us. However, my brother was a beast — a linebacker in wrinkly new skin with chipmunk cheeks and juicy thighs. He was also completely a surprise.

According to David Marzano, M.D., an OB-GYN at University of Michigan Von Voigtlander Women’s Hospital, there are a bevy of myths which abound about big babies. He told the university's Health Blog that you are possibly worrying yourself needlessly, and noted that the doctors get pretty darned good at guessing your baby's size through the use of a method of palpating the baby through the uterus — flawed though it may be — and evaluating that in conjunction with personal and family history to determine if your baby will be too big. “After a few years of experience, you get pretty good at predicting how big a baby is going to be with this method, but sometimes you’re surprised," he said. In which case, doctors are prepared.

While the reasons for a big baby are pretty straight forward, whether or not that means that your baby will be too big to deliver are not. It used to be that if the OB-GYN thought that your baby was going to be born large, they took you in for a C-section and that was that. Now, according to the new guidelines written by the American College of Obstetrics and Gynecology (ACOG), the thought is that new mothers should be allowed to labor, and labor longer than previously permitted, and also push for a longer period of time, especially if an epidural is used. They wrote that it is still very much at the discretion of the OB-GYN and hospital, and that there are extenuating circumstances, like heart rate fluctuations, maternal stress, and birth presentation that may yet prevent a vaginal delivery.

However, it is less and less likely that you will be told that your baby is too big for delivery, as they wrote that research shows that mothers can deliver much larger babies than previously thought, and that the benefits of a vaginal delivery often outweigh the risks of the C-section. No, a 10-pound baby isn't going to be a bucket of fun to manually evacuate from your vagina, but it might just be possible.