Macrosomia: Baby who is much larger than average

About 9 percent of all babies are born with macrosomia. Macrosomia (hypersomia, gigantism) is a symptom in which a baby is born much larger than average. On average, babies weigh between 2,500 grams and 4,000 grams. Babies with macrosomia are in the 90th percentile or higher in weight for their gestational age when they are born at term. Macrosomia has a number of causes, such as diabetes mellitus (diabetes) and obesity (obesity). When a baby is born larger than normal, this causes a number of complications during delivery but also for the baby later in life. Regular prenatal care, a healthy weight, good control of diabetes and regular exercise are some of the advice to prevent macrosomia.

  • Causes of macrosomia
  • Risk factors of baby being much larger than average
  • Symptoms
  • Diagnosis and examinations
  • Complications
  • Mother
  • Baby
  • Birth
  • Prognosis for mother and child


Causes of macrosomia

Causes of macrosomia include:

  • diabetes mellitus in the mother
  • a medical condition in the baby
  • genetic conditions such as
    • Beckwith-Wiedemann syndrome: condition with abnormal growth
    • the Bannayan-Riley-Ruvalcaba syndrome: condition with tumors
    • Cantú syndrome: condition with abnormalities of the heart, hair and face
  • genetic factors
  • obesity in the mother


Risk factors of baby being much larger than average

A woman is more likely to have a baby with macrosomia if she:

  • have high blood pressure during pregnancy
  • have had a previous baby with macrosomia
  • suffers from diabetes mellitus before becoming pregnant, or develops pregnancy during pregnancy (gestational diabetes)
  • more than two weeks after the due date
  • is older than 35 years
  • gaining too much weight during pregnancy
  • is obese during pregnancy
  • being pregnant with a boy



The main symptom of macrosomia is a birth weight of more than 4 kg, regardless of whether the baby was born early, term or late.

Diagnosis and examinations

The doctor asks the woman about her medical history and past pregnancies. He checks the size of the baby during pregnancy, but this measurement is not always correct. He uses various possible methods such as:

  • a biophysical profile: This test combines the nonstress test with an ultrasound to monitor the baby’s movements, breathing and the level of amniotic fluid.
  • an ultrasound: This test uses sound waves to view an image of the baby in the womb. Although it is not completely accurate in predicting birth weight, it does give an idea of the size of the baby in the womb.
  • a measurement of fundus height (the length from the top of the mother’s uterus to her pubic bone – a greater than normal fundus height may indicate macrosomia)
  • a measurement of the amniotic fluid level: polyhydramnios (excess amniotic fluid) indicates that the baby is producing a lot of urine; big babies urinate more.
  • a nonstress test: This test measures the baby’s heart rate when he or she moves.



The risks associated with fetal macrosomia increase greatly when birth weight exceeds 4,500 grams. Both mother and baby may experience complications.


Maternal problems due to macrosomia include:

  • Uterine rupture : If a woman has previously had a cesarean section or uterine surgery, the uterus may rupture during childbirth. This complication is potentially life-threatening.
  • Bleeding after delivery : Due to a large baby, proper contraction of the muscles of the uterus does not occur, which may lead to excessive bleeding.
  • Injury to the vagina : When the baby is born, a tear or other injury may occur.



Macrosomia sometimes also causes complications in the baby:

  • Abnormal blood sugar levels : Some babies are born with lower than normal blood sugar levels (hypoglycemia) due to macrosomia. less often the blood sugar level is too high (hyperglycemia).
  • Obesity : Heavier weight babies are more likely to be obese in childhood.

Babies born large are at risk for these complications in adulthood:

  • high blood pressure
  • diabetes
  • obesity

Furthermore, babies born with macrosomia also have a chance of developing metabolic syndrome. This cluster of conditions includes high blood pressure, high blood sugar, excess belly fat and abnormal cholesterol levels. As the child grows older, metabolic syndrome increases the risk of conditions such as diabetes mellitus and heart disease.


Macrosomia causes problems during childbirth.

  • The baby is not getting enough oxygen.
  • The birth takes longer than normal.
  • The delivery should be done by caesarean section: If the doctor suspects that the size of the baby will cause complications during a vaginal delivery, a caesarean section may be necessary.
  • The baby’s shoulder may become stuck in the birth canal
  • An assisted birth (with forceps or vacuum cup) is required.
  • A fracture of the baby’s collarbone or other bone occurs


Prognosis for mother and child

A cesarean section is sometimes recommended to ensure a healthy delivery. Inducing labor early so that the baby is born before the due date does not affect the outcome. Babies born large should have regular checkups for health conditions such as obesity and diabetes as they grow. By controlling pre-existing conditions and health during pregnancy, and monitoring the baby’s health into adulthood, it is possible to prevent complications.

read more

  • Cesarean section: Operation to deliver baby