Fat moms and fat babies? Weight gain during pregnancy

Heidi Mallis and Anna E. Mazzucco, Ph.D.


Updated 2014

The obesity epidemic in the U.S. is affecting newborns and pregnant women. New guidelines for gaining weight during pregnancy aim to reverse the current trend, where women gain too much weight, causing health problems for the mother and her baby.

Twenty years after the previous guidelines were issued, the Institute of Medicine released updated guidelines in 2009 for weight gain during pregnancy.[end  Institute of Medicine (2009, May). Weight gain during pregnancy: re-examining the guidelines. Retrieved from http://www.nationalacademies.org/hmd/~/media/Files/Report%20Files/2009/Weight-Gain-During-Pregnancy-Reexamining-the-Guidelines/Report%20Brief%20-%20Weight%20Gain%20During%20Pregnancy.pdf (Accessed November 30, 2009).] The report concluded that women today are heavier when they become pregnant than women used to be, and they gain more weight during their pregnancy than before. This can harm the health of both the mother and the baby.


What are the risks associated with being overweight or obese during pregnancy?

An obese woman is less likely to go into labor naturally (or even to have it induced successfully), which means she is much more likely to have a Caesarean section. Obesity during pregnancy also increases the risk of several birth defects, such as cleft palate, intestinal tract abnormalities, and heart defects.[end Rowlands I, Graves N, de Jersey S, McIntyre D, Callaway L (2009, October 12). Obesity in pregnancy: outcomes and economics. Seminars in fetal and neonatal medicine: 1744-65.]

When a baby’s birth weight is greater than 10 pounds, known as macrosomia (which merely means heavy birth weight), the baby is likely to grow up to be an obese child. Obese children tend to remain obese during their teenage years and as adults.

A study conducted by researchers at Virginia Tech College of Veterinary Medicine showed that a diet high in saturated fat among pregnant mice was associated with the offspring developing chronic disease in adulthood. The adult offspring had signs of hyperglycemia (high levels of sugar in the blood), insulin resistance, obesity, and hypertension, despite being fed healthy rodent food.[end Liang C, Oest M, Prater M (2009, September 11). Intrauterine exposure to high saturated fat diet elevates risk of adult-onset chronic diseases in C57BL/6 mice. Birth Defects Res B Dev Reprod Toxicol. -Not available-, ahead of print.]  This finding is significant because it shows that a child’s healthy eating habits can’t necessarily make up for a mother’s poor eating habits during pregnancy.

There is also evidence that children may have a higher risk of developing asthma if their mothers are overweight when they get pregnant. Obesity increases the amount of cytokines (which are small proteins) circulating in the body that cause inflammation, which is a type of immune response. When a pregnant woman’s body is in a constant state of inflammation due to excess fat (as opposed to weight gain from the developing fetus), it affects the lung development of the baby in the womb and may lead to a higher risk of asthma symptoms in childhood.[end Scholtens S, Wijga A, Brunekreef B, Kerkhof M, Postma S, Oldenwening M, de Jongste J, Smit H (2009, September 29). Maternal overweight before pregnancy and asthma in offspring followed for 8 years. International Journal of Obesity. -Not available-, ahead of print.]

A study of pregnant women in the Netherlands found that women who had excessive weight gain during pregnancy were eating more, were not physically active, and also were not getting enough sleep. The relationship between too little sleep and obesity has been known for several years: people who do not get enough sleep tend to eat more, and people who are obese tend to have sleep apnea, resulting in less sleep.[end Patel SR, Hu FB (2008). Short sleep duration and weight gain: a systematic review. Obesity, March 2008; 16(3): 643-653.]


Pregnancy Weight Gain: Too much isn’t good but neither is too little!

While these studies make it clear that gaining an unhealthy amount of weight during pregnancy isn’t beneficial for the mother or the baby, research also suggests that gaining too little weight during pregnancy isn’t a good thing either.   A study published in 2014 found that babies from mothers who gained less than the recommended amount of weight tended to have higher levels of pesticides in the fluid in their umbilical cords than those from mothers who gained the recommended amount of weight.[end Vizcaino E, at al. Gestational Weight Gain and Exposure of Newborns to Persistent Organic Pollutants. Environmental Health Perspectives. May 2014.]

The reason may be because many pesticides get stored in body fat.  Women who don’t gain enough weight during pregnancy may use more of their body fat to nourish their growing baby, which means that the pesticides stored there will enter the blood of both the mom and the baby.

While we don’t know exactly how which pesticides or how great the exposure of pesticides are harmful to a growing baby, many experts recommend avoiding pesticide and toxin exposures during this sensitive time of growth and development.  Studies have shown that pesticide exposures in the womb can cause problems with brain, reproductive and immune system development.  For more information on pesticides and children’s health, see our article here.[end Forns J, Lertxundi N, Aranbarri A, Murcia M, Gascon M, Martinez D, et al. 2012. Prenatal exposure to organochlorine compounds and neuropsychological development up to two years of life. Environ Int 45(1): 72-77.],[end Herbstman JB, Sjodin A, Apelberg BJ, Witter FR, Halden RU, Patterson DG, et al. 2008. Birth delivery mode modifies the associations between prenatal polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) and neonatal thyroid hormone levels. Environ Health Perspect 116(10):1376-1382.],[end Hertz-Picciotto I, Park HY, Dostal M, Kocan A, Trnovec T, Sram R. 2008. Prenatal exposures to persistent and non-persistent organic compounds and effects on immune system development. Basic Clin Pharmacol Toxicol 102(2):146-154.] For information on avoiding unsafe chemical exposures both before and during pregnancy, check out this article.

Gaining too little weight can also increase a mother’s chances of giving birth too early, or having a baby that is much smaller than average, which can sometimes lead to other health problems for the baby later in life.[end Stotland NE, et al. Gestational weight gain and adverse neonatal outcome among term infants. Obstet Gynecol. 2006 Sep;108(3 Pt 1):635-43.],[end Mumbare S, et al. Maternal Risk Factors Associated with Term Low Birth Weight Neonates: A Matched-Pair Case Control Study. Indian Pediatr 2012;49: 25-28.] Overall, studies support the Institute of Medicine recommendations for healthy weight gain, neither too little or too much.  And, having a healthy weight and balanced nutrition before getting pregnant will make it easier to keep weight gain during pregnancy within the recommended range.


Tips for maintaining a healthy weight during pregnancy

Many women find that their usual strategies for keeping their weight down don’t work during pregnancy. For example, when clothes get tight or the scale shows a few extra pounds, that is usually a reminder to watch what you eat; but those clues are not helpful for a women who is pregnant.

The following suggestions can help a woman stay healthy during pregnancy:

Underweight: BMI less than 18.5 kg 28-40 No guideline available
Normal weight: BMI between 18.5-24.9 kg 25-35 37-54
Overweight: BMI between 25.0-29.9 kg 15-25 31-50
Obese: BMI greater than 30.0 kg 11-20 25-42
  • Discuss these guidelines with a health care provider to create a personalized plan that best meets your pregnancy needs.
  • Maintain a healthy diet, emphasizing foods that are low in fat and high in fiber. In addition to prenatal vitamins, aim for foods that are a natural source of folic acid (also called folate), such as orange juice, green leafy vegetables, beans, peanuts, broccoli, asparagus, peas, and lentils. Folic acid can reduce the risk of birth defects of the brain and spine.
  • Participate regularly in physical activity. The American College of Obstetricians and Gynecologists recommends a minimum of 30 minutes of moderate physical activity a day for pregnant women (unless there are medical or obstetric complications). Of course, avoid activities with a high risk of falling or abdominal harm.[end American College of Obstetricians and Gynecologists (2002, January). ACOG Committee Opinion No. 267: Exercise during pregnancy and postpartum period. 99 (1): 1-3.]

By maintaining a healthy weight, it is possible to reduce the risk of complications during pregnancy and delivery, and decrease the chances of your child developing health problems later on.