The Myth of the Big Baby

My friend had been pushing for four hours.

“You have a size nine baby coming out of a size seven pelvis,” her doctor said.

I heard several similar stories while reporting on elective deliveries. The baby is too big to push out.

My friend’s daughter was 8 pounds 11.5 ounces. She was born, eventually, by Cesarean section.

Not, technically, a “big baby.” 

Big Baby Syndrome is also known as Large for Gestational Age or fetal macrosomia. Sometimes, it’s defined as babies born weighing 4,000 grams - 8 pounds 13 ounces - or more. Sometimes, the cutoff is 4,500 grams - 9 pounds 15 ounces.

In my friend’s case, it turns out her doctors may actually have been most worried about shoulder dystocia – which is when the baby’s head fits through the woman’s vagina, but the shoulders get stuck.

“It’s all about shoulder dystocia,” said Theresa Morris, birth researcher and associate professor of sociology at Trinity College in Connecticut. “I don’t think women realize that physicians are obsessed with this."

There’s a reason docs are worried. Shoulder dystocia can lead to complications, such as palsy -- temporary or permanent -- stemming from injury to the baby’s brachial plexis nerve, near the collarbone. It can also lead to vaginal tearing and hemorrhaging.

Shoulder dystocia is unpreventable and unpredictable. Perhaps that’s what makes it so scary for care providers.

Reported rates vary.

One study from the American Journalism of Obstetrics and Gynecology  said that shoulder dystocia occurs infrequently, with rates ranging from 0.2 percent to 3 percent of all vaginal deliveries. 

Shoulder dystocia is connected to big babies because big babies are more likely to get stuck. But here’s the rub: Accurate birth weight is hard to predict.

Using ultrasound to determine birth weight late in pregnancy is unreliable. Morris says it can be off 16-20 percent. That means a nine-pound baby could turn out to be only seven.

If your doctor says your baby may not fit and you need a Cesarean section, know that a suspected big baby is not a medical reason to have surgery. Experts say that often the best outcome for mother and baby comes from paying close attention to labor, rather than performing a C-section (on the chance that the baby will get stuck).

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