In every pregnancy, a woman starts out with a 3-5% chance of having a baby with a birth defect. This is called her background risk. This sheet talks about whether obesity may increase the risk for birth defects over that background risk. This information should not take the place of medical care and advice from your health care provider.

What is obesity?

Obesity is a condition that is associated with too much body fat. More than one-third of women in the United States have weights that fall in the obesity range. One measure of obesity is body-mass index (BMI) which is an estimate of body fat based on height and weight. A person is said to be obese when their BMI is 30 or higher. For someone who is 5 foot 6 inches tall, a healthy non-pregnant weight range is 115 to 154 pounds. This same person is considered obese at 186 or more pounds. You can find your healthy weight range at https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/english_bmi_calculator/bmi_calculator.html. If you do not have access to the internet, your local library can help.

What about weight gain during pregnancy?

Weight gain during pregnancy is expected. The ideal amount of weight gain during pregnancy will vary with your pre-pregnancy BMI and the number of babies that you are carrying. Women who are overweight or obese may be encouraged to limit any weight gain during pregnancy. In general, a total weight gain of 15–25 pounds (lb) for overweight women (BMI=25–29.9) and 11–20 lb for obese women (BMI ≥ 30) is recommended. Please work closely with your healthcare provider to determine how much weight you should gain during pregnancy.

Can obesity during pregnancy cause miscarriage or birth defects?

Maternal obesity has been associated with a higher chance for miscarriage and with a higher chance for certain birth defects, such as problems with the heart and spine. However, the overall increased risk for miscarriage and/or birth defects is likely to be small. For example, about 1-2 babies of every 1,000 born will have a neural tube defect, which occurs when the spine or skull does not close properly. Obesity may double that risk, meaning that the actual increased risk is still small at 2-4 babies out of 1,000 babies born.

Ultrasounds are used to screen a pregnancy for birth defects. Obesity may make it harder for birth defects to be seen.

Can obesity cause pregnancy complications?

Obesity has been found to increase the chance for gestational diabetes and high blood pressure during pregnancy. Obesity might also cause an increased chance of premature delivery (babies born before 37 weeks of pregnancy) and stillbirth. Also, newborns of mothers with obesity are at an increased chance for large body size (macrosomia) which can make delivery more complicated and increases the risk that the baby will have childhood and adult obesity. Obesity has also been associated with a greater chance for c-section delivery.

Can my obesity during pregnancy cause problems with learning in my child?

Some studies have suggested a possible association with learning difficulties in children born to obese mothers. However, this is difficult to study and other studies are needed to better understand if there is an association.

Should I try to lose weight while pregnant?

Weight loss is generally not recommended during pregnancy. Ideally, weight loss should be done prior to pregnancy. If you are already pregnant and overweight or obese, limiting weight gain may be recommended. Talk with your healthcare provider about your recommended weight gain, nutrition and exercise.

What about having maternal obesity while breastfeeding?

Maternal obesity is not considered a reason for concern with breastfeeding. Be sure to talk to your health care provider about all of your breastfeeding questions.

Is it safe for the father of the baby to have obesity?

Studies have found that obesity in men can reduce fertility (make it harder for them to get a partner pregnant). In general, exposures that the fathers have are unlikely to increase risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures and Pregnancy at https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/pdf/.

Selected References:

  • American College of Obstetricians and Gynecologists. 2013. ACOG Committee opinion no. 549: Obesity in pregnancy. Obstet Gynecol. 121(1):213-7.
  • American College of Obstetricians and Gynecologists. 2013. ACOG Committee opinion no. 548: Weight Gain During Pregnancy. Available at: https://www.acog.org/-/media/Committee-Opinions/Committee-on-Obstetric-Practice/co548.pdf?dmc=1&ts=20180102T2046334047
  • Cai GJ, et al. 2014. Association between maternal body mass index and congenital heart defects in offspring: a systematic review. Am J Obstet Gynecol. 211(2):91-117.
  • Castro LC and Avina R. 2002. Maternal obesity and pregnancy outcomes. Curr Opin Obstet Gynecol. 14:601-606.
  • Cedergren MI. 2004. Maternal morbid obesity and the risk of adverse pregnancy outcome. Obstet Gynecol. 103:219-224.
  • Gilboa SM, et al. 2010. Association between prepregnancy body mass index and congenital heart defects. Am J Obstet Gynecol 202:51.e1-10.
  • Hall LF and Neubert AG. 2005. Obesity and pregnancy. Obstet Gynecol Surv 60(4):253-260.
  • Huang l, et al. 2014. Maternal prepregnancy obesity and child neurodevelopment in the Collaborative Perinatal Project. Int. J Epidemiol. 43(3):783-92.
  • Johnson J, et al. 2013. Eunice Kennedy Shriver National Institute of Child Health; Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU) Network. Pregnancy outcomes with weight gain above or below the 2009 Institute of Medicine guidelines. Obstet Gynecol. 121(5):969-75.
  • Nuthalapaty FS and Rouse DJ2004. The impact of obesity on obstetrical practice and outcome. Clin Obstet Gynecol 47:898-913.
  • Stothard KJ,et al. 2009. Maternal overweight and obesity and the risk of congenital anomalies: a systematic review and meta-analysis. JAMA. 11;301(6):636-50.
  • Tanda L, et al. 2013. The impact of prepregnancy obesity on children’s cognitive test scores. Matern Child Health J. 17:222-229.