How Your OB Can Tell You're Going To Have A Big Baby

If you’re currently pregnant or have been pregnant, there’s a 100 percent chance you’ve had unsolicited predictions about your pregnancy and baby. Carrying high? It’s a boy. Did you gain weight in your thighs instead of your tummy? Definitely a girl. If you were a big baby when you were born, your baby is definitely going to be big, too. Let’s say you want to get your information from actual doctors that base their observations on science and have the knowledge from past experiences with patients — can your OB really tell if you’re going to have a big baby?

"To be frank, you can’t always tell because there are a number factors involved. We monitor the baby’s growth, however, by measuring from the pubic bone to the fundus of the uterus (top of the uterus), and the number of centimeters measured roughly corresponds to gestational age by week," Dr. Kathryn Wright with Facey Medical Group, Mission Hills, says in an email to Romper.

OB-GYN, NP, CNM Risa Klein says the very first thing she reviews is the mother’s nutrition. With that and her measuring the baby’s growth by feeling him at every visit, she’s able to tell how big the baby is.

"I feel her abdomen at every single prenatal visit, measure the fundal growth, and, coupled with her weight gain, I get a good idea of how the baby is growing," Klein says to Romper in an email. She continues:

"I ask my moms to fill in a nutrition sheet of what they’re eating for a week, and then I tweak my mom’s nutrition to get her off to the right start so her baby will be growing on healthy foods, especially protein, dark green veggies, and whole grains. Too many carbs, white flour, sweets, sugars, milk and dairy, can up the ante on the baby’s weight."

Birth and postpartum doula Liza Maltz agrees that nutrition plays a key role in how large your baby will be. "Be mindful of nutrition from the beginning. So many times, mom comes to me frantic that they were told they have a big baby," she says in an email to Romper. "I try to speak with clients about good nutrition from the beginning without scaring them."

Even with all the right nutrition and weight gain, how can your baby still be measuring too big or too small? For some babies, it depends on how big their parents are. "Some babies are longer because their dads are over 6 feet tall, and that’s normal for that baby," Klein says.

Wright says if you’re measuring larger or smaller than expected, she checks an ultrasound, because sometimes there is too much or too little amniotic fluid, so the ultrasound can detect that, too. She notes that unfortunately, ultrasounds are only approximations, and can even be as much as a pound off.

"This is where the doctor’s judgment comes in," Wright says. "How big does the woman’s abdomen look? How much did her last baby or babies weigh? Does she have gestational diabetes or a large weight gain in pregnancy? All of these factors together help us make the decision on whether to recommend a cesarean delivery for fetal macrosomia (a large baby)," she adds.

According to Wright, the normal range of a baby that is carried to term is 6 pounds, 9 ounces to 8 pounds, 15 ounces. Abnormally large babies are anything over 4000 grams, or approximately 9 pounds. But when does it become unsafe to deliver vaginally? How big is too big? "The American College of Obstetricians and Gynecologists recommends considering elective cesarean delivery over 4500 grams (9 pounds, 14 ounces) for diabetic moms, and over 5000 grams (11 pounds, 8 ounces) for non-diabetic moms," Wright says. "In practice, however, many mothers would prefer a cesarean delivery if they believe their baby will be over 9 pounds, regardless of diabetic status. On the other hand, if a mother has previously had a 10 pound baby with no problems, then it is reasonable to consider vaginal delivery with a second child close to 10 pounds."

Worried about delivering a large baby? Don't be — your body was designed for this. "The good news is that the natural hormones of pregnancy, including relaxin, soften the pelvis to accommodate the baby," Klein says.

But that doesn't mean you're out of the clear. Wright says there can be a cause for concern if you do have a really large baby, other than how painful it will be. "Ultimately, our biggest concern is shoulder dystocia, which is when the head delivers, and the shoulders get stuck — this can result in injury or even death to the baby, and injury to the mother," she says. Unfortunately, Wright says dystocia is difficult to predict, and can happen with any size baby for a variety of reasons.

But don’t fret. The bottom line is, your body knows what it's doing and, most of the time, doctors can predict if your baby is going to be too large for a vaginal delivery. Unless your partner is a linebacker for the Packers, and you’re unusually tall, chances are your baby will be just the right size for your body.