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Macrosomia: Everything About Excessive Fetal Growth

Medically reviewed by Ruben Macapinlac, MD, DPPS · Pediatrics · Philippine Pediatric Society

Written by Nikita Bhalla · Updated Sep 05, 2022

Macrosomia: Everything About Excessive Fetal Growth

Macrosomia is a term that describes a newborn who is strikingly larger than an average baby. The weight of a normal newborn baby is 3kgs to 3.3kgs at birth. A baby suffering from this condition weighs more than 4.5kgs or 9.9 pounds, no matter what the baby’s gestational age has been. The condition is also known as fetal macrosomia.

Studies have shown that 8% of infants born worldwide are affected by this condition. Most babies with macrosomia are healthy, without additional complications. But the ones whose weight is on the higher side, for instance above  4kgs or 9 pounds, might face some health issues. 

Does My Baby Have Fetal Macrosomia?

It’s quite difficult to know whether your baby has macrosomia while they are still in the womb.  You typically come to know about it while or after giving birth to your baby.

Although an ultrasound scan can tell you about your baby’s size, it may not always be precise, especially when the pregnancy comes to full term. The difference is about 10%.

When an ultrasound scan shows that your baby is comparatively big for the current period, you might be asked to do a blood test for your blood sugar levels. Women with gestational diabetes are more likely to give birth to babies with macrosomia.

Maternal Signs That May Indicate A Macrosomial Baby

Signs that may point to this condition may include:

Fundal Height

This is the height between the top of your uterus and the pubic bone. A larger than normal height is a sign of your baby having fetal macrosomia.

Feeling Your Abdomen

Manually feeling your abdomen can also help you sense if your baby’s size feels larger than an average one. It doesn’t hurt the baby, so you need not worry about it.

Amniotic Fluid

Amniotic fluid is a fluid that covers and safeguards the baby during pregnancy. An excess amount of amniotic fluid — a condition known as polyhydramnios, is associated with macrosomia. Amniotic fluid is formed by the baby’s urine. A larger baby produces more urine, hence causing excessive amniotic urine.  

Causes of Fetal Macrosomia

Gestational diabetes is probably the most likely cause of macrosomia. Other factors which can lead to the condition include but are not limited to:

  • Having high body mass index (BMI) during early pregnancy
  • Excessive weight gain during pregnancy and between pregnancies
  • No weight loss from the previous pregnancy
  • Baby is overdue (by two weeks or more)

The weight of a baby varies depending on ethnicity and gender. Baby boys often weigh more than baby girls. The chance of macrosomia also gets higher if your first child had fetal macrosomia. 

Complications in Fetal Macrosomia

Although there may be some difficulties, giving birth vaginally to a large baby is possible. Two-thirds of large babies are born by vaginal delivery. 

Your labor time may be longer if your baby has this condition. One out of five cases of macrosomia will need assisted birth. Complications include heavy bleeding and serious perineal tearing. The birth is likely to be easier for those who have experienced normal delivery before, without any complications.

The likelihood of having shoulder dystocia (the baby has difficulty passing the birth canal) during delivery is 1 in 13. The chances almost double if the baby is more than  5kgs or 11 pounds. Shoulder dystocia is a condition wherein the baby’s shoulders get stuck after their head is out. Severe cases need urgent medical intervention. You may require assistance and instruction by medical experts with respect to when to push, when to hold, and what position to adjust, in order to free the baby’s shoulders successfully.

If you are overdue, an induction may be performed. However, inducing may not always be helpful either. Mothers with diabetes should have an induction at week 38. Elective caesarean is also a good choice to prevent complications during childbirth.

Newborn and Childhood Risk in Fetal Macrosomia

Besides the complications during birth, there are other health complications associated with macrosomia, which your baby may face:

Low Blood Sugar Levels

If a baby is born with macrosomia, chances are that they will also be diagnosed with lower than normal blood sugar levels.


Studies have shown that babies born with macrosomia are more prone to childhood obesity as their weight increases. 

Metabolic Syndrome

If your baby was born with fetal macrosomia, they are at a greater risk of developing metabolic syndrome during their childhood. 

Prevention of Fetal Macrosomia

You might not be able to completely prevent or have complete control over macrosomia. But certain precautions can help you have a healthy pregnancy and baby.

Watch Out for Your Weight

If you are obese or gain excess weight during your pregnancy, book an appointment with your doctor and work towards getting back to a healthy body weight for you. Around 25-30 pounds of weight gain is normal and healthy. 

Diabetes Under Control

If you develop gestational diabetes or had it before your pregnancy as well, consult your doctor and work towards getting your diabetes under control. This will help you curb complications, including macrosomia. 

Some Physical Activity Every Day

After consulting your doctor, take part in physical exercises or activities that suit you and your current health status. 

Fetal Macrosomia and the Baby’s Wellbeing

Most babies with macrosomia are healthy. However, babies who experience shoulder dystocia may face some problems with their shoulder and arm nerves.

Chances of nerve damage are 2% to 16%. This can result from improper handling by medical assistants or the pressure of contractions during birth. Fortunately, treatment for this nerve damage is possible.

Key Takeaway

Macrosomia refers to newborns who weigh more than average, more than 4.5kgs or 9.9 pounds.. Although most babies with macrosomia are healthy, the condition may lead to some health complications. Consult with your doctor on how to lower the chances of macrosomia by managing the possibility of gestational diabetes.

Learn more about Baby’s First Year here.


Hello Health Group does not provide medical advice, diagnosis or treatment.

Medically reviewed by

Ruben Macapinlac, MD, DPPS

Pediatrics · Philippine Pediatric Society

Written by Nikita Bhalla · Updated Sep 05, 2022

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