1. ¹Division of Nutritional Sciences, Cornell University, Ithaca, New York, USA
2. ²Department of Pediatrics, Bassett Healthcare, Cooperstown, New York, USA

Correspondence: Kathleen M. Rasmussen (kmr5@cornell.edu)

Received 25 June 2007; Accepted 27 August 2007.

Abstract

The latest nationally representative data show that 28.9% of American women of reproductive age (20–39 years old) are obese (BMI 30 kg/m²) and 8.0% have reached extreme obesity (BMI 40 kg/m²), an all-time high (1). These statistics are associated with other, equally disturbing trends. First, we have reached an all-time high in the proportion of women who deliver by cesarean section, 29.1% in 2004, the latest national data (2). Higher prepregnant BMI values are associated with a greater risk of cesarean delivery (3) and increases in maternal prepregnant weight as well as conditions associated with higher weight account for a substantial proportion of the recent increase in cesarean delivery (4). Second, we have also reached an all time in the proportion of children and adolescents who are overweight (95th percentile of age- and sex-specific BMI), 17.1% among 2–19 years olds (1). Much attention has recently been devoted to the tripling in childhood overweight that has occurred since 1980, with particular reference to genetic factors and lifestyle changes that might have contributed to this increase in prevalence. In this Perspective, we draw attention to the importance of obesity among women of reproductive age for their own later health as well as that of their children.

Obese women may have difficulty becoming pregnant. This is thought to result from menstrual dysfunction and anovulation, "possibly because of altered secretion of pulsatile gonadotropin- releasing hormone, sex hormone–binding globulin, ovarian and adrenal androgen, and luteinizing hormone, and also because of altered insulin resistance" (5). Weight loss improves the probability of conception as it restores ovulation (6). Similarly, weight gain after one birth leads to an increase in waiting time to a subsequent conception (7). Paradoxically, obese women may also be at risk of unintended pregnancy from contraceptive failure (8). Together, these characteristics may make it more difficult for obese women to plan their pregnancies.

Obese women have a significant excess risk for many complications during pregnancy, including gestational diabetes mellitus and preeclampsia (9,10). These risks increase with increasing maternal prepregnant BMI (3,10,11). Women with these complications are at risk of early development of chronic diseases (12). For instance, there is evidence that women who experience gestational diabetes mellitus are at excess risk of developing type 2 diabetes earlier than those who have not had this problem (13,14). This is also true for preeclampsia, chronic hypertension (15), and ischemic heart disease (12,16); however, the proportion of this long-term risk that is attributable to maternal obesity is unknown.

Obese women are also more likely to undergo elective or emergency cesarean sections and to have their labor induced than normal-weight women (9). This results, in part, from their excess risk of delivering a large-for-gestational age infant (9). Cesarean delivery is more difficult in obese than normal-weight women (17) and is associated with excess risk of wound infection in obese women (9). Cesarean section itself is associated with a longer recovery than vaginal delivery as well as a delay in first putting the baby to the breast to nurse (18). Such delays may cause a reduction in the duration of breast-feeding (19), possibly because of a delay in the onset of copious milk secretion, although this association is not consistent (20,21,22,23).

Finally, women who are obese at the time of conception are less likely to attempt breast-feeding (9,24). Among women whoever attempt to breast-feed their newborns, obese women are more likely than normal-weight women to cease breast-feeding in the first few days after delivery (25,26) and to breast-feed exclusively or to any extent for shorter periods (24,25,26,27). This association has been observed among white women in the United States (25) and elsewhere (24,27,28,29), Hispanic women in the United States (26) but not black women in the United States (26). Moreover, the heavier the woman, the shorter her duration of breast-feeding (29). High weight gain in pregnancy adds to the obese woman's risk for shortened duration of breast-feeding (29,30). This reduction in breast-feeding may make it more difficult for obese women to return to their prepregnant weight postpartum.

Obese women are more likely than normal-weight women to give birth to a large (>4,000 g or >90th percentile of weight-for-gestational age) baby (31,32). Having a large baby is associated with substantial obstetric morbidity (31). In addition, macrosomic babies suffer excess morbidity themselves (33), are more likely than normal-weight infants to have a low Apgar score at birth and be admitted to a special-care nursery, but they are equally likely to be breast-fed (31). Of course, not all macrosomic babies are born to obese women. Preliminary evidence (34) indicates that large-for-gestational age infants, as a group, breast-feed for as long as or longer than normal-weight infants.

The reduction in breast-feeding that has been observed among obese women also has consequences for their infants. They do not receive the full benefits of breast-feeding. Moreover, they are then exposed to the disadvantages of early use of infant formula and also early introduction of solid foods (35). This complex of behaviors leads to excess weight gain during the first year of life in both American (36) and Danish infants (37).

Much attention has been paid to the link between gaining weight early in childhood and the development of obesity later in childhood and on to adolescence and adulthood. Some of this is undoubtedly associated with parental, primarily maternal, obesity (38,39,40), although there is controversy about whether this association results from genetic factors or continuation of the environmental and familial circumstances that contributed to or sustained parental obesity.

From this brief review, it is apparent that there may be a number of ways to intervene early enough to prevent the development of childhood obesity. First, it is clearly important to assure that women conceive at a healthy weight. This may require that a higher proportion of women plan their pregnancies than has historically been the case (41) and that obese women lose weight before conception. It is essential that such women be protected from the risk of pregnancy during the weight-loss period if the full reproductive advantages of weight loss are to be achieved (42,43). Second, women should be advised and assisted to restrict their weight gain during pregnancy to the ranges recommended by the Institute of Medicine (44) as higher gains are associated with poorer breast-feeding performance (29). Third, women should be advised and assisted to breast-feed for as long as practical for their own situations in accordance with the recommendations of the American Academy of Pediatrics (45).

Additional research is needed to evaluate the feasibility and effectiveness of these and other possible interventions to address the consequences of maternal obesity for the woman herself and her child. For example, it is unknown whether an obese woman who loses weight before conception would acquire the same ability to breast-feed successfully as a woman who was never obese, although it has been observed that large maternal weight loss from bariatric surgery prevents the transmission of obesity to their children (46). The interventions that have been developed to help women to limit their weight gain during pregnancy have had only limited success (47,48), so research is needed to improve their effectiveness. Given the known difficulty of weight loss before conception and of limiting weight gain during pregnancy to the recommended ranges, it is also important to develop feasible and effective interventions to assist obese women to normalize their weight in the postpartum period. Most important, it is essential to develop feasible and effective interventions to improve the success of breast-feeding among obese women for their own health and that of their children.