Obesity, Diabetes in Pregnancy Can Mean Dangerously Large Baby

Health Writer

It’s clear that entering pregnancy diagnosed with obesity or developing diabetes during pregnancy are not healthy scenarios for mother or baby. Researchers at the University of Cambridge wanted to determine whether excessive overgrowth of infants during pregnancy was directly correlated to a diagnosis of maternal obesity and gestational diabetes. They also wanted to determine how early on in pregnancy the excessive growth spurt begins.

What is gestational diabetes?

When a pregnant woman who has no prior history of diabetes develops glucose intolerance during pregnancy, she is diagnosed with gestational diabetes. Risk factors for gestational diabetes include obesity at the time of pregnancy, excess weight gain in the first and second trimester of pregnancy, becoming pregnant at an older age, having a family history of Type 2 diabetes, and the mother having had a low birth weight herself when she was born. Certain races and ethnicities are also at higher risk of developing the disease.

During pregnancy, the placenta actually releases hormones that can lead to a buildup of sugar in your blood. Obesity can complicate this phenomenon since insulin resistance is associated with obesity. Uncontrolled blood sugar levels will likely lead to gestational diabetes.

How do obesity and gestational diabetes affect fetal growth?

We already know that children born to women who have gestational diabetes have a higher risk of being obese by the time they are around age six. If you have gestational diabetes, then your offspring’s risk of developing diabetes also increases. If you are obese and have gestational diabetes, it is likely that your baby will be larger than normal, which can make delivery difficult. You may need a C-section because a vaginal delivery is too dangerous. Your baby can also have other complications, including dying before or soon after birth. Obesity during pregnancy can also lead to preterm birth.

When is screening for gestational diabetes performed?

The U.S. Preventive Services Task Force currently recommends screening pregnant women after the 24th week of pregnancy for blood sugar abnormalities. The position of the task force is that there does not appear to be additional benefits of screening before 24 weeks of pregnancy.

The American Congress of Obstetrics and Gynecologists (ACOG) advises earlier screening for women at increased risk of gestational diabetes, including women who have been diagnosed with obesity. If the woman screens as “negative,” then a glucose tolerance test, or GTT, should be repeated between 24 and 28 weeks of pregnancy.

This study suggests that screening for gestational diabetes earlier in pregnancy may help to prevent an overly large baby, especially if the mother has a co-morbid condition of obesity. The study suggests that the baby can already be overly large by week 20 if the mother is obese. The same growth pattern is likely in the presence of gestational diabetes.

The study model

About 4,000 first-time mothers were followed through their entire pregnancy. About four percent were diagnosed with gestational diabetes around the 28th week of pregnancy. Using ultrasound scans the researchers found that:

  1. The obese mothers were 63 percent more likely to have abnormally large babies by week 20, compared to thinner mothers.

  2. Women eventually diagnosed with gestational diabetes at or after week 28 had babies who were twice as likely to be overly large by week 28, compared to the babies of women not diagnosed with diabetes.

  3. Women diagnosed with obesity and gestational diabetes had the fastest growing babies. These babies were five times more likely to be overly large by week 28, compared to the women who had neither diagnosis.


This study suggests that babies born to women who are obese and go on to develop gestational diabetes are five times more likely to be larger than normal — excessively larger — by the sixth month of pregnancy. This phenomenon also sheds light on the fact that the fetal growth spurts often occur well before a screening will identify gestational diabetes.  This suggests that current screening practices for diagnosing gestational diabetes identify the disease later in the process, at a point where intercepting or counteracting the effect of diabetes on the growing baby is less likely to have an impact.

The study’s findings suggest that earlier screening practices for obesity and gestational diabetes risk should be considered, though it is not clear if routinely testing earlier in pregnancy would actually benefit the mothers or the babies.

What is clear, however, is that we need to identify at-risk women early on in pregnancy and then initiate a lifestyle program that can intercept health consequences in the growing fetus. Women who start pregnancy overweight or diagnosed with obesity should strongly adhere to the new guidelines for weight gain during pregnancy.

Tips for a healthier pregnancy:

  • If you are overweight or obese, consider losing weight before getting pregnant.
  • If you are already pregnant, work with your OB/GYN to limit weight gain during pregnancy if you are diagnosed with obesity or have a strong family history of Type 2 diabetes.
  • Begin prenatal care early and have regular doctor visits.
  • If you have more than one risk factor for gestational diabetes, create an early screening plan with your OB/GYN so you catch it early and treat it early.
  • Consider working with a dietician and a personal trainer to create a lifestyle program that limits your risk of gestational diabetes and obesity.
  • Do not heed the mantra “eating for two” as a license to consume large portions of even healthy food, let alone junk food, fast food, and other treats. Yes, you will gain weight during pregnancy, but there is a safe range of weight gain that you need to acknowledge, especially if you are already overweight or diagnosed with obesity as you start your pregnancy.

See more helpful articles:

Carbohydrates Can Be Bad and Good for You

A Primer on Insulin Resistance

Losing Weight and Fat While Maintaining Muscle: Hard, but Doable