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Macrosomia: Things to Know Why Your Baby Measures Big

Rakshitha S

Sep 21, 2023

When you’re expecting a baby, there’s no question that you will be excited about the little bundle of joy on the way. But for some moms-to-be, it’s not just excitement—it’s also worrisome.

Some babies are born with macrosomia, meaning they weigh more than the normal range for their gestational age. When this happens, it can be scary for both mom and baby.

Here’s what you should know about macrosomia, including why it happens, how it can affect your pregnancy, and if there’s anything you can do to prevent it.


What Is Macrosomia?

As a first-time parent, you may be excited about buying everything your baby needs, from diapers to the design of their nursery rooms. However, finding out your child is expected to be larger than average may ruin your excitement.

It is known as fetal macrosomia when an unborn child is projected to be bigger than normal. An estimated weight of 4,500 grams, which is equivalent to 9 pounds and 15 ounces, is considered fetal macrosomia. At 37 weeks or more, an estimated weight of 4 kilograms can also be considered the same.


What Happens if My Baby Is Too Big for Delivery?

In some cases, delivering a baby that is too big can be risky for both mother and baby.

The following complications may occur:

  • Cephalopelvic disproportion (CPD) – This occurs when the baby’s head is too large to pass through the pelvic bones.
  • Fetal distress – Labor can be slowed down or stopped when a baby is distressed. The longer labor takes, the greater the risk of complications for both mother and baby.
  • Maternal lacerations – Maternal exhaustion from pushing out a large baby can tear the vagina (lacerations), which increases the risk of infection.
  • Shoulder dystocia – Large babies are more likely to suffer from shoulder dystocia (when the shoulder gets stuck during delivery). This can be dangerous for both mother and baby because it can damage nerves in the shoulder and neck of the newborn and affect their ability to breathe properly. The risk of this happening is higher if there has been a previous C-section.


What Causes Macrosomia?

A combination of factors causes this birth defect. The baby’s genetics are a major factor. If your family has a history of large babies, there’s a good chance that you’ll have one too.

Another factor is maternal weight gain during pregnancy. The more weight you gain during pregnancy, the greater the chance your baby will be large.

Macrosomia can also be caused by increased insulin-like growth factor (IGF) levels, which stimulate fetal growth. Women with diabetes are at higher risk of having macrosomic babies. 

It is more likely to occur in pregnancies that go on for longer than 42 weeks.


What Are the Symptoms of Fetal Macrosomia?

Fetal macrosomia symptoms

An ultrasound may be recommended to determine the fetal weight and amniotic fluid levels. In ultrasound, sound waves are transmitted through tissues at a high frequency. Waves can be used to create images, whether video or photographic, to check for fetal macrosomia symptoms.

Ultrasound can only approximate a fetus’ weight to within roughly 10%. The ultrasound estimate of 9 pounds represents the “best guess,” but the actual weight of your baby may range from 8 to 10 pounds.

Your ultrasound, pregnancy history, and physical exam will determine the timing and method of delivery for your baby. Shoulder dystocia cannot be diagnosed accurately with ultrasound.

Your healthcare professional will assess whether or not you need an ultrasound exam. Take a feel of your belly. For determining the fetus size, your healthcare professional may palpate particular parts of your abdomen.

Your prenatal care physician may offer additional testing to monitor the fetus’ health if the results indicate its size. A biophysical profile or a non-stress test would be appropriate in this context.


What Moms Should Remember When Their Baby Is Big

Several adjustments are made to the care of babies with suspected macrosomia. The healthcare professional may advise you to have a cesarean delivery if your baby is expected to weigh over 5,000 grams (11 pounds). For diabetes and a baby weighing more than 4,500 grams (9 pounds, 15 ounces), your provider may recommend a cesarean birth.

In cases of fetal macrosomia, induction of labor at an early stage is not recommended. There is a two-fold increase in the likelihood of cesarean delivery with labor induction. Furthermore, your kid is not protected from hazards.

A doctor or midwife might hesitate to offer assistance in the form of a vacuum or forceps if the pushing stage takes an unusually long time. Using a vacuum or forceps to deliver a large baby increases the risk of shoulder dystocia, nerve damage, and brain bleeding in the infant. 


How Moms Can Prevent Macrosomia

Avoiding pre-eclampsia, gestational diabetes, and preterm birth:

  • Preventive measures include eating a healthy diet, exercising regularly, not smoking, and avoiding alcohol. In addition, women with a family history of macrosomia should discuss the risk with their doctor.
  • Monitor your weight gain regularly. One of the best ways to prevent macrosomia is to keep track of your weight gain during pregnancy. Talk with your doctor about how much weight you should gain during each trimester, and work closely with them to ensure you do not gain too much or too little weight.
  • Avoid eating a lot of sugar during pregnancy. Sugar can cause your body to produce insulin, increasing breast milk production. This may lead to an increase in blood glucose levels. Thus, consuming too much sugar might result in macrosomia for your babies.



How common is macrosomia?

While it's difficult to determine the exact prevalence of macrosomia, it's estimated that about 9% of babies are born with this condition.

How will I know if my baby has macrosomia?

If your baby's head circumference is greater than expected for the gestational age at birth, the baby may be born with macrosomia. Talk to your doctor if you're concerned about your baby's growth during pregnancy. They can monitor your baby's weight and let you know if there are any concerns.

What are some of the drawbacks of macrosomia?

Macrosomia can make labor and delivery more challenging. This increases the likelihood of the mother undergoing a cesarean section and the infant being injured during birth. Macrosomic babies are more likely to develop obesity and diabetes later in life than babies born without the condition.

When does macrosomia start?

The fetus's development does not stop even when pregnancy continues. Fetal macrosomia increases the risk when pregnancy goes on for more than 40 weeks. If the amniotic fluid is abundant, this could indicate a larger baby. The quantity of urine a baby generates is influenced by the amount of amniotic fluid surrounding the infant.



Macrosomia is a condition that is caused by excessive fetal size. It is usually associated with gestational diabetes and may be caused by obesity. 

A baby with macrosomia can have problems during the birth process. Shoulder dystocia happens when the baby’s shoulders get stuck during delivery because they are too large to fit through the birth canal. Healthy diets before and during pregnancy can prevent macrosomia from developing with careful pregnancy planning.

Rakshitha S

Rakshitha's goal is to empower parents to make confident decisions about their baby's care and well-being. She believes that every parent deserves access to high-quality, reliable information, and is committed to providing that through her writing and expertise.

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