Obesity is the accumulation of excess body fat. Maternal obesity is the accumulation of excess body fat during pregnancy to the extent that it increases the risk of negative outcomes for both the mother and fetus. Pregnant women in the overweight or obese categories have a higher risk for pregnancy-related complications such as gestational diabetes, preeclampsia, cesarean delivery, and infertility. The in utero environment of the mother also places the fetus at greater risk of having birth defects, preterm birth, stillbirth, excess birthweight (fetal macrosomia), and childhood obesity. In addition, both mother and baby have increased risk for developing diabetes and heart disease later in their lives.
Obesity is more than excess weight. It is a complex clinical state that involves physical, physiologic, hormonal, genetic, cultural, socioeconomic, and environmental factors. Overweight and obesity are commonly defined using body mass index (BMI), a ratio of weight in kilograms divided by height in meters, according to criteria of the World Health Organization (WHO). The WHO criteria define overweight as a BMI between 25 kg/m2 and 30 kg/m2; obesity is defined as having a BMI of 30 kg/m2 or greater. Extreme obesity is any BMI value over 40 kg/m2. The health risks associated with overweight and obesity are derived from excess adipose (fatty) tissue. Adipose tissue itself is an essential component of the body and has diverse functions such as providing nutritional, hormonal, and structural support. The cells in adipose tissue are adipocytes that store fats to provide a future energy source. Adipose tissue also contains nonfat cells such as fibroblasts and immune cells. Together the fat and nonfat cells secrete substances (peptides, hormones, cytokines) that influence organ function, including the abnormal endocrine functions associated with obesity. Obesity develops in adipose tissue that is excessive beyond the point of appropriate function.
Maternal obesity compromises maternal health and has a significant impact on fetal development and the child's health during childhood as well in later life. Risk of obstetric complications in overweight or obese pregnant women increases from early pregnancy through childbirth. Risk of spontaneous abortion (miscarriage) in early pregnancy is increased. Risk of having a stillborn infant is double that of women with average weight and pregnancy weight gain. Congenital (at birth) defects such as spina bifida and congenital heart disease are increased in newborns of obese mothers. In later pregnancy, hypertensive disorders of pregnancy such as preeclampsia are more likely in obese mothers. Risk of preterm birth is increased as well as the likelihood of cesarean section, which is 47% in obese women compared to 20% in nonobese. Gestational diabetes mellitus is a significant risk, occurring in 2.6% of obese pregnant women. In addition, anesthesia-related complications, excessive blood loss, and blood clots in the extremities (postpartum thrombophlebitis) occur more frequently in the presence of maternal obesity.
Maternal obesity is also associated with adverse long-term effects for the mother and her offspring, especially a tendency toward the continuation of maternal obesity and greater risk of overweight or obese status in the child. Research results show that excess weight gain during pregnancy and retention of that weight one year postpartum are strong predictors of overweight or obesity in the woman ten years later.
Obesity in pregnancy often stems from the mother's prepregnancy overweight or obese status. In 1990, the Institute of Medicine (IOM) and the National Heart, Lung, and Blood Institute of the National Institutes of Health introduced guidelines recommending different gestational weight gain limits based on women's prepregnancy BMI. The ultimate goal was to improve infant birth weight and to avoid complications for both mother and baby. PRAMS data collected over ten years showed that the national guidelines had almost no effect on weight gain in pregnant women, with only one in three women meeting the recommended thresholds. These results suggested that policies should focus on maternal and child health through dietary measures rather than merely providing guidelines for weight gain.
The most significant risk factor for maternal obesity is prepregnancy obesity. Behavioral and lifestyle factors, especially dietary patterns, are found to contribute to maternal obesity more than demographic factors such as age, race/ethnicity, education, and socioeconomic status. Thus, women who were overweight or obese prior to pregnancy are most likely to gain excess weight during pregnancy.
Symptoms of obesity, other than physical appearance, will vary between individuals because variations in overall health status will influence which symptoms develop. Some women may have preexisting diabetes, food sensitivities, carbohydrate intolerance, high blood pressure (hypertension), and gastroesophageal reflux disease (GERD), a condition in which stomach contents and acid rise back up into the esophagus after eating or on exertion. As pregnancy advances through the trimesters, insulin resistance typically increases and, in obese women, may trigger metabolic dysfunction that can progress to gestational diabetes. Blood glucose must therefore be monitored in obese women throughout pregnancy, from the time of the first prenatal care visit. Nocturnal apnea, interrupted sleep, and airway obstruction of some kind may occur in obese pregnant women. Obese patients may also have physical limitations to participating in strenuous exercise, and ongoing counseling is recommended both for exercise and diet.
Diagnosis of maternal obesity is a simple matter of evaluating prepregnancy BMI and gestational weight gain.
In obese pregnant women, careful observation for and prevention of pregnancy complications associated with excess gestational weight gain and obesity may require modifying the routine prenatal care provided during pregnancy. Adjustments to prenatal care associated with obesity and possible complications may include:
A prelabor consultation with an anesthetist is recommended by the American College of Obstetricians and Gynecologists (ACOG) for all pregnant women with BMI over 40 kg/m2. Early epidural placement is also advised during labor and the placement of the epidural catheter needs frequent checking if cesarean delivery is a consideration.
Treatment for overweight or obesity in most individuals is usually a matter of losing weight safely. In most cases, weight loss during pregnancy is not advised because restricting food intake could be dangerous for the mother and developing fetus. Rather than attempting a serious weight loss diet, avoiding weight gain is the safest and most attainable goal. Maternal obesity is accompanied by an extra reserve of calories stored in adipose tissue, so maintaining the present weight or even losing a little weight is generally not harmful.
If a pregnant woman's BMI is between 25kg/m2 and 29.9kg/m2, the recommended weight gain according to IOM guidelines is between 15 and 25 pounds by the end of the pregnancy, which equals about two to three pounds per month in the second and third trimesters. If the BMI is 30kg/m2 or higher, only 11 to 20 pounds should be gained during pregnancy. Pregnant women who gain more than the recommended weight are twice as likely to develop gestational diabetes than those who stay within the limits.
Appropriate physical exercise and following a healthy dietary plan can help overweight or obese pregnant women avoid weight gain during pregnancy and reduce risk of complications. Women with maternal obesity are advised to consult with their obstetrician and a nutritionist or dietician to find the most appropriate dietary plan for maintaining weight throughout a healthy pregnancy.
The ideal time for bodyweight intervention is preconception. Physicians caring for obese women who are planning a pregnancy have an opportunity to provide preconception counseling and patient education. Planning may include contraceptive measures until the woman's weight and overall health status have improved. Dietary and exercise interventions prior to pregnancy increase the opportunity for the woman to have a healthier pregnancy with better outcomes for her and her baby.
A high consumption of refined food products, unhealthy fats, added sugars and low intake of fruits and vegetables is consistently linked with excess weight gain during pregnancy. Dietary plans that emphasize plant-based eating, minimal red meat consumption, low dairy, low saturated fats and zero trans fats, no added sugars, no sugar-sweetened beverages, and even minimal fruit juice are associated with healthier weight status. This low-calorie dietary plan may actually result in weight loss but a gradual small or modest loss rather than dramatic decreases.
A pregnancy diet designed to minimize weight gain focuses on colorful fruits and vegetables that are low in calories and filled with essential vitamins and minerals, lean protein sources, and fiber. The benefits of plant-based or plant-rich dietary patterns during pregnancy include protective effects for the health of mothers and babies. Studies have shown that maternal nutritional patterns that include low intake of plant-based foods (e.g., fruits, vegetables, beans, nuts, and seeds) increases the risk of pregnancy complications such as preeclampsia and maternal obesity and contributes to birth defects in newborns and increased susceptibility to illness and overweight/obesity during childhood. A balanced diet with all of the essential nutrients is necessary during pregnancy; vegetarian, vegan, and plant-based diets may lack specific nutrients that are required for a healthy pregnancy. Omega-3 fatty acids, for example, are important, along with vitamin B12, vitamin D3, iron, zinc, and iodine, to protect fetal health status. B12 is only provided through consumption of animal products and supplements. Flax, flax seeds, and flax oil can provide a good supply of omega-3 fatty acids in a plant-based diet. If animal products have been eliminated completely, nonheme iron can be obtained from certain foods, although the heme iron contained in animal products is assimilated better in the body. Vitamin D can be obtained through sun exposure for at least 15 minutes per day in appropriate climates, but this does not preclude deficiency in areas or seasons where sunlight is minimal. Consuming a whole, plant-based diet that includes plant proteins and the limited inclusion of dairy and meat products has the potential to supply all essential nutrients, including vitamin B12, vitamin D3, and heme iron that are typically lacking in vegetarian and vegan diets. Because plant-based diets that are not balanced may be deficient in specific nutrients that are particularly relevant during pregnancy, women on plant-based diets must be guided by the advice of an obstetrician, dietician, or nutritionist.
Because obesity is associated with reproductive system dysfunction, including infertility, one healthful diet, in particular, that is directed toward improving reproductive status and increasing a woman's fertility may also provide benefits to women with maternal obesity. Nutrition experts have even cited the fertility diet and its basic components as conducive to good health in anyone, not just women who are trying to become pregnant. In fact, the fertility diet is ranked as the #1 “Best Diabetes Diet” in Easiest Diets to Follow (. https://health.usnews.com/best_diet/best-easy-diets ). The fertility diet has several benefits of particular value in relation to pregnancy among obese women. For example, consuming whole grains instead of refined carbohydrates that force the body to produce extra insulin can be a protective measure against developing diabetes or gestational diabetes, as well as preventing vascular problems that may lead to heart attack and stroke. Also, replacing meat protein with slowly metabolized carbohydrates and plant proteins, as recommended by the fertility diet, improves the health of veins and arteries and increases blood flow, which is essential for conception and throughout pregnancy. Although variations of the fertility diet have been designed by different individuals and organizations, the basic guidelines remain the same, including:
An increasing number of obese pregnant women have already undergone bariatric surgery, and these women will have increased fertility postoperatively. If pregnancy occurs because birth control measures were not used to prevent pregnancy for at least a year after the surgery, nutrition will be especially important to avoid unwanted weight gain. Restricting food intake is not advisable during pregnancy, and the postoperative dietary recommendations still need to be followed. Nausea experienced in early pregnancy may interfere with getting sufficient nutritional support, but may also help women to lose a few pounds. Pregnancy may also be emotionally stressful, and some women may turn to eating to ease stress. In addition, women who are still plus-sized after undergoing weight loss surgery are still at risk for pregnancy-induced hypertension and gestational diabetes, although the risk is less than before the surgery. Close monitoring of nutritional status, blood sugar (glucose) levels, and blood pressure will be needed throughout pregnancy. Risk of cesarean delivery is also more likely in women who have undergone weight loss surgery than in those who have not. Avoiding weight gain, exercising during pregnancy, and taking childbirth preparation classes may help to reduce risk of cesarean section.
Maternal obesity has long-lasting effects on both the mother and baby and is associated with multiple complications during and after pregnancy, including continued obesity in the mother and likely obesity in the child. Obesity in pregnancy is associated with greater risk of preterm birth and stillbirth, prolonged pregnancy, difficult labor, and higher risk of cesarean delivery. Obstetric and neonatal outcomes are decidedly poor compared to those of women with normal prepregnancy weight status and recommended weight gain during pregnancy. Obstetricians need to monitor obese pregnant women throughout pregnancy, labor, and delivery to address possible complications associated with pregnancy, anesthesia, and fetal development.
See also Adult nutrition ; American Diabetes Association ; Diabetes mellitus ; Gestational diabetes ; Obesity .
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L. Lee Culvert