Fetal macrosomia

Fetal macrosomia is used to describe a newborn with an excessive birth weight. Perinatal diagnosis of macrosomia is difficult and inaccurate. Newborns weighing above 4000 g are considered as macrosomic. Macrosomia is encountered in 1-10% of pregnancies. It can complicate vaginal delivery and put the baby at risk for injury at the time of birth. There are chances of increased health risks for a macrosomic baby.

Macrosomia occurs when the baby receives nutrition more than required. Excess nutrition makes the baby grow faster and bears an unusual weight. Ultrasound examination is useful to determine the size of the baby, but it may not be accurate. If the baby is identified as macrosomic, then the pregnant mother will be closely monitored for the difficulties that may occur at the time of delivery. Sometimes a c-section or induction might be necessary for the delivery of the baby.


Some of the symptoms that indicate fetal macrosomia are:

Large Fundal Height: The doctors measure the distance between the top of the uterus to the pubic bone. A larger distance indicates large fundal height, which is an indication for a fetal macrosomia.
Excessive Amniotic Fluid (Polyhydramnios): Amniotic fluid surrounds the baby in the uterus. The amniotic fluid reflects the baby’s urine output; more urine is produced if the baby is large. Too much of amniotic fluid may be an indication for excessive weight of the baby.

Maternal Risks

Delivery Problems: The delivery of a macrosomic baby is difficult as the baby cannot pass through the birth canal easily, so vacuum or c-section is required.

Uterine Rupture: If a prior c- section was performed in the first delivery, the fetal macrosomia can be a serious complication as the uterus tears open from the scar of the c-section line.

Lacerations of Genital Tract: Fetal Macrosomia can injure the birth canal by tearing the vaginal tissues and muscles, sometimes anal muscles are also.

Bleeding: Fetal macrosomia can lead to uterine atony which may result in excessive bleeding after delivery of the baby.


There is no treatment for fetal macrosomia. If the diagnosis indicates fetal macrosomia, the doctors may suggest vacuum-assisted vaginal delivery or a c-section based on the condition of the mother. Mostly the doctors suggest c-section if the mother has gestational diabetes or the baby’s weight is more than 500 g. It is also suggested in cases where the first delivery resulted in shoulder dystocia of the baby.


A number of factors contribute to a macrosomic baby. Genetics is the most significant factor that is involved in the growth and development of the baby. So, the genes may also be the reason for a macrosomic baby. Other factors that contribute to fetal macrosomia are:

  • Gestational diabetes or diabetes mellitus during pregnancy
  • Extra weight gain during pregnancy
  • Carrying the baby more than past due date
  • Gender of the baby (Most males are macrosomic)
  • High body mass index (BMI) during first few months of pregnancy
  • Macrosomic baby in first pregnancy
  • Weight gain in between pregnancies or no weight loss after first pregnancy

Sometimes these conditions may not affect the delivery; the macrosomic baby can be delivered easily without complications. In some cases, macrosomic babies are also born to the mothers with none of the risks mentioned above.


Fetal macrosomia can pose health risks for both the mother and the baby.

Newborn Risks

Obesity: Macrosomic infant may have an increased risk for childhood obesity.

Low Blood Sugar Levels: Babies with macrosomia are more likely to have lower blood sugar levels than the normal.

Metabolic Syndrome: Metabolic syndrome includes cluster of conditions such as increase blood pressure, increased sugar levels, excessive body fat and cholesterol, increased risk of heart diseases, stroke, and diabetes. The infant of diabetic mother is more likely to experience metabolic syndrome.

Prediction of the weight of the baby is difficult before birth. It is possible and accurate only after the birth. Your doctor would suggest the following tests if he or she suspects fetal macrosomia.

Ultrasound:The doctors may suggest an ultrasound at the end of the third trimester, to measure the parts of the baby such as head, abdomen, and femur. The measurements of these body parts will be used to determine the weight of the baby. However, this weight may not be accurate.
Antenatal Testing : Some doctors may suggest antenatal testing to identify fetal macrosomia. The antenatal testing includes nonstress test or a fetal biophysical profile.

In nonstress test, the heart rate of the baby is measured, based on the movement of the baby.

In the fetal biophysical test, nonstress test is performed with ultrasound, to monitor the movement of the baby, breathing, and volume of the amniotic fluid.

You may not prevent fetal macrosomia, but you need to makes some lifestyle changes to promote healthy pregnancy:

  • If you are panning for pregnancy, talk to your doctor dietician and take proper diet to reach healthy weight
  • Control your blood sugar levels to avoid gestational diabetes
  • Follow your doctor’s instructions and exercise daily
  • Monitor your weight by gaining healthy amount of weight