Does Size Matter? Macrosomia or Big Baby

If your healthcare provide or midwife has suggested you to plan for a C-section, continue reading:

If a baby weighs over 4kg (8lb 13oz), which is larger than average, it is known as Macrosomia (weighing over gestational age). Confirmation of a big baby, with a better result, can be provided by an ultrasound scan. These results are not always accurate and the post baby weight can change (by 10%). So keep in mind, only a post birth weight alone can actually confirm. There is though, a higher chance of maternal and fetal health being at a higher risk of certain complications.


What Causes A Big Baby?

Your practitioner may have already recommended tests to be run on gestational diabetes since it’s the most influential factor in a baby’s weight. Pre-existing diabetes also plays a vital role. Variation in birth weight can go unexplained, but you can have a big baby if:

  • You haven’t lost weight from your previous pregnancy or have gained weight between pregnancies.
  • Your body mass index (BMI) is in the obese/overweight range at the start of your pregnancy.
  • You have drastically gained weight during your pregnancy.
  • You’re two weeks passed the due date.

Genetics and even the sex of the baby (boys commonly weigh more than girls) are also predictors of macrosomy. ACOG (American College of Obstetricians and Gynecologists) do not recommend an induction of labor, however, healthcare providers may suggest a labor induction and Cesarean section for a suspected macrosomic baby.


Risk Factors Associated With Macrosomia:

A C-section comes with the risk of any major surgery, but it is considered a relatively safer delivery. However, it is not unheard of for women to naturally deliver babies that have weighed over 4.5lb. The risks your practitioner will assess to avoid delivering a macrosmic baby vaginally, are divided into 3 groups:

  1. Maternal risks: The passage of a large fetus through the birth canal puts the mother at the risk of-
  • Longer labor and increased need for a C-section
  • Lacerations or tearing (eg: perineal, vaginal, cervical)
  • Hemorrhage or heavy blood loss
  • Complications associated with major abdominal surgery which include bleeding, infections and damage to adjacent organs (eg: bladder, uterus, fallopian tubes, ovaries, intestines, uterer).
  • Complications associated with regional and general anesthesia.
  1. Fetal risks: Based on five major assumptions-
  • Baby’s shoulder getting stuck in the cervix (shoulder dystocia- 1 in 13 chances)
  • Physical pressure can cause birth trauma (damage to nerves, tissues and organs).
  1. Neonatal risks: The above average weight of the baby increases the risk of-
  • Hypoglycaemia (low blood sugar- 50%)
  • Electrolyte disturbances
  • Blood disorders (eg: polycythemia)

When delivering a big baby, progression of labor is slow and more painful. The cervix may not open enough to allow the baby to descend completely (head pushed out but stuck in the birth canal). This rare complication is an indicator to your healthcare provider to administer an emergency C-section. Commonly, big babies will be fine. In the off-set, the child experienced shoulder dystocia (nerve damage occurs in between 2% and 16% of babies who have shoulder dystocia), birth trauma or even a broken collar bone, there are still high chances of the little one recovering fully.


Born weighing 15lbs, a healthy, little girl from Karnataka, India is the current record holder for the world’s heaviest baby girl. 1. The heaviest baby ever, was born in Ohio, USA, in 1879. His birth weight was a whooping 23lb 12oz .2.

Talk to your healthcare provider or midwife about when the need for labor induction arises. Compare the risks of C-section with that of delivering a baby naturally. If you or your child will not benefit in any way through vaginal birth, your safest choice would be to trust your healthcare provider and go with whatever they decide, in order to avoid complications.