Obesity is a strong determinant of obstetric morbidity and mortality. This chapter summarizes the current state of knowledge of the relationship between obesity and adverse maternal outcome, including effects on the health of the pregnant mother as well as complications at the time of delivery. Total body fat can be measured by direct methods such as dual energy X-ray absorptiometry (DEXA) and magnetic resonance imaging (MRI). Maternal obesity is overrepresented in maternal deaths in developed countries. Obese pregnant women have an increased incidence of labor induction. The evidence shows a marked increased risk of adverse obstetric events in obese pregnancies, including gestational diabetes, hypertensive diseases, thromboembolism, infection, cesarean section, and postpartum hemorrhage. There are also clear indications that risks increase as body mass index (BMI), or the levels of obesity, increase. In most developed countries the prevalence of obesity is around 20%.

This chapter reviews data highlighting the vulnerability of obese women to multiple micronutrient deficiencies. It summarizes the evidence supporting the effectiveness of nutrition interventions at preventing key birth outcomes among obese pregnant women. Increased body mass index (BMI) in non-pregnant women is associated with decreased serum folate, ascorbic acid, vitamin E, total carotenoids, and selenium in a variety of populations. With the poor micronutrient status of obese women of childbearing age, and potentially the same relationship in obese pregnant women, it is critical to understand whether micronutrient interventions could positively impact birth outcomes in obese pregnancy. Several high-quality observational studies of birth defects, pre-eclampsia may provide additional insight into whether micronutrient supplementation may reduce the likelihood of poor outcomes among obese pregnant women. Future rigorous observational studies exploring a wide range of micronutrients and risk of poor outcomes of women with high pre-pregnancy BMIs will add to the evidence base.