Big Babies: When Your Your Fetus is Above the 90th Percentile

There is no one in the world who is more concerned about how your baby is going to fit through your pelvis than you. Being told your fetus is in the 90th percentile is nerve-wracking. Which is why I get so upset with how some providers approach a conversation about a suspected big baby based on ultrasound measurements. I'm not talking about folks with other medical diagnoses, like gestational diabetes. I'm talking about perfectly healthy, low-risk folks. I've had this conversation twice this week with two different clients, so now I'm just going to go off.

What does big baby even mean? A baby might be labeled as "big" if they are measuring at or above the 90th percentile.

• The technical term is large for gestational age

• To get a true diagnosis of fetal macrosomia your baby must weigh 4000 grams, or about 8lb 13oz at birth regardless of gestational length; this diagnosis cannot be given from ultrasounds even if they are estimating your baby's weight is above 4000 grams

  • Average birth weight is around 7lb 6oz according to the WHO

• Risks rise when the baby weighs in at 4500 grams, or 9lb 15oz, about the 97th percentile at birth

• An extremely large baby is over 5000 grams or 11lbs

Anecdotally, I have had many clients who have been told they have a suspected big baby who then go on to deliver a slightly larger (think: around 8lb) but definitely not macrosomic baby. I feel frustrated on behalf of my clients who spend the last weeks of their pregnancy worrying extra over something that generally they are already worried about. What pregnant person isn't constantly thinking, "How am I going to get this baby out???"

The largest baby I have seen born was 9lb 12oz and that baby was born peacefully into water at a birth center during an unmedicated labor. No one suspected that the baby was big. There was no pressure from the midwives about pushing quickly or forcefully. My client listened to her body and birthed her baby in her own time. She had a small first degree tear (most common tear type is second degree). I was so proud of that person for choosing a team of providers that aligned so well to her desires for birth. She may have had a different experience in another setting.

What Increases Your Risk of Having a Big Baby?

You are more at risk of having a baby that is large for gestational age if:

• Big babies run in your family, or you yourself were a big baby (genetics)

• The baby's sex is male

• You have diabetes, either before pregnancy and/or during

• You've had other big babies prior to this baby

• All the risk factors docs love to bring up: higher BMI, older age, past your due date

According to the NHS, "most babies, even large babies, will have no problems."

We grow babies that are the right size for our bodies. So what is all the fuss about? The fuss is generally about providers and their nervous systems. I'm in my "everything is about the nervous system" era and I will not apologize for it. There are some extremely rare complications associated with babies over 4500 grams (9lb 13oz). Providers see a LOT of birth and so chances are that they have seen those complications.

One complication is shoulder dystocia, which occurs just as often in big babies as in smaller babies, but doctors tend to really worry about it. Add onto that the fact that injuries related to shoulder dystocia are one of the most common reasons for litigation against doctors. Then, add onto that that giving birth on your back - the preferred position for most docs - also closes your pelvis and makes it difficult to do some of the maneuvers that help baby's shoulders make it past your pubic bone.

You put all of those factors together and you get providers who really want to avoid vaginal birth if they suspect it will be hard or complicated. A larger baby stresses them out. In fact, the biggest risk associated with having is a suspected big baby is just that - your provider suspecting it!

Bottom line: many providers have a bias against suspected big babies.

How Likely is a Big Baby?

One out of 3 people are told at the end of their pregnancy that their baby is big. At minimum, every third person in America is told they will have a big baby. But if it is the 90th percentile, how could that be possible? Your baby is supposed to be the largest out of 10. The math is not mathing.

From Evidence Based Birth:

Although only one in ten babies is born large, researchers found that ...one out of three families in the study were told that their babies were too big. In the end, the average birth weight of their suspected “big babies” was only 7 lbs., 13 oz. (Declercq, Sakala et al. 2013).

Of the people who were told that their baby was getting big, two out of three said their care provider discussed inducing labor because of the suspected big baby, and one out of three said their care provider talked about planning a Cesarean because of the big baby.

In other words, you are very likely to be told you have a big baby and then have your provider recommend induction or cesarean. Even though you may in fact not have a big baby on your hands, and inductions and cesareans have no been shown to decrease risks.

FAQs

Is there anything I can do to prevent a big baby?

There isn't much that you can do. It is hard to accurately predict a big baby. As with pregnancy in general, a nutritious diet and regular exercise will help. Get screened for gestational diabetes.

If you would like to prevent the suspicion of a big baby, you can forgo the ultrasounds at the end of pregnancy that are meant to measure baby's size. They are fairly inaccurate anyway. If you have no medical reason for an ultrasound (remember, suspected big baby is not a medical reason), then you can opt out. Sure, you won't get to see your baby on the screen, but you may save yourself a whole lot of stress and worry.

What are the risks associated with a big baby?

What is shoulder dystocia?

How accurate are the ultrasounds to predict big babies?

Are there better outcomes for people who have an induction for a suspected big baby?

Should I just have a cesarean?

I have had clients who are told, right off the bat, that since their baby is likely in the 90th percentile they may want to consider an elective cesarean. Not only does this undermine my client's confidence in themselves and their bodies, it also undermines their confidence in the care team to safely deliver the baby. You need to feel safe and empowered in order for the labor hormones to flow and a suspected big baby does not do you any favors. This is where choosing a place to birth at that has both providers AND policies that support your preferences is key.

Want to learn more? Try listening to this Evidence Based Birth podcast, which summarizes the recent research.

As with all of my blog, I am writing from my perspective. Doulas don't give medical advice - we help clients achieve true informed consent through information and data. I am a doula and therefore none of this is medical advice.