Are You Having a Big Baby? 5 Signs to Know

At some point, most pregnant people wonder how big their baby will be. Sure, it's fun to guess your little one's size and birth weight, but there are some practical reasons for the inquiry, too.

Take newborn baby essentials, for example. Should you stock up on newborn diapers, or will you need preemie sizes? Will you skip the newborn onesies and head straight to 0–3 month attire?

Another common worry is the delivery experience itself. Bigger babies (who have a condition called fetal macrosomia) are associated with a higher risk for certain complications—both for the baby and the birthing parent. These include prolonged labor, postpartum hemorrhage, fetal distress, increased risk of birth injuries like shoulder dystocia, and more.

Predicting your baby's size isn't an exact science, but here are some signs that you're having a big baby, plus the potential risks to know beforehand.

What Is Fetal Macrosomia?

Medically speaking, there are a few terms to know for having a big baby: "large for gestational age" and "fetal macrosomia."

Large for gestational age: This means a fetus is measuring larger than expected when accounting for their time in the womb. Common causes include gestational diabetes or obesity in the pregnant person, as well as excessive weight gain while expecting.

Fetal macrosomia: This refers to any baby born weighing more than 4,000 grams (8 pounds, 13 ounces). Research indicates that it occurs in 3% to 15% of pregnancies.

Signs You're Having a Big Baby

During pregnancy, health care providers use a few methods to predict a baby's size at birth, although no method will be 100% accurate. Here are some likely signs that you're having a big baby.

Your bump measures larger than average

One way to estimate fetal size is based on your belly measurement, specifically from your pubic bone to the top of your uterus (called fundal height). If your bump measures larger than expected for how far along into pregnancy you are, your baby may be also larger than average.

That said, other factors might cause a larger-than-expected fundal height. For example, having obesity or uterine fibroids can lead to inaccurate measurements, according to the American College of Obstetricians and Gynecologists (ACOG). So if you measure large more than once, a health care provider may recommend an ultrasound for a more accurate picture of your baby's size.

You have extra amniotic fluid

If a health care provider says your amniotic fluid levels are higher than usual, this could also be a sign that you're having a big baby. Studies have found that extra amniotic fluid (a condition called polyhydramnios) is associated with a three times greater risk of having a baby with macrosomia.

But again, extra amniotic fluid can have many different causes (such as gestational diabetes), and it is not always a guarantee you'll have a large baby. Because more amniotic fluid could be a sign of having a big baby or other complications, your health care provider will likely want to monitor it.

Your ultrasound predicts a large baby

Ultrasounds are better indicators of fetal size, but they're not always accurate. In fact, according to a 2018 systematic review, ultrasounds tend to overestimate how big babies are. Even if a health care provider estimates that you've got a big baby based on ultrasound images, their actual weight at birth may be less than initially thought.

You have had a large baby before

In general, people tend to deliver heavier babies with each pregnancy. And while it's not a hard-and-fast rule, if you have had one or more large babies in the past, you're up to 10 times more likely to have a big baby again in the future.

You have gestational diabetes

People with gestational diabetes often have larger-than-average babies, especially if the diabetes is not controlled well with diet or insulin. Studies have found that without gestational diabetes, the risk of fetal macrosomia is around 12%, but with gestational diabetes, the risk is 15% to 45%.

Potential Risks of Having a Big Baby

Fetal macrosomia comes with some risks for both the pregnant person and the baby. And the bigger the baby, the greater the likelihood of complications.

For the gestational parent, studies show that risks of having a big baby include:

• Prolonged labor
• Postpartum hemorrhage
• Perineal trauma
• Increased risk of C-section
• Uterine rupture
• Birth injuries, like pelvic bone separation and nerve damage

Babies diagnosed with fetal macrosomia are also at risk for certain health complications, such as:

• Shoulder dystocia (a baby's shoulders get stuck during birth)
• Fetal distress
• Erb's palsy (nerve damage that causes arm paralysis)
• Fracture of the clavicle or humerus
• Breathing problems
• Low blood sugar levels
  
• Jaundice

There is also some evidence that large babies may develop insulin resistance later in life, which can cause additional medical complications such as childhood diabetes and obesity.

You Might Be Having a Big Baby—Now What?

Learning about the potential risks of fetal macrosomia might be overwhelming, but it's important to keep in mind that having a big baby doesn't necessarily mean that something will go wrong. Indeed, if your health care provider suspects that you're having a big baby, they'll monitor you and your baby's health, and if any complications are suspected, they'll devise a plan to minimize risks.

The best thing a pregnant person can do is eat a nutritious diet, exercise as recommended by your provider, and manage any health conditions that arise.

After your baby is born, if their size is larger than average, they'll likely get their blood sugar tested to ensure they can stabilize their blood sugars. But if all checks out, it's back to your arms for some big baby snuggles!