INTRODUCTION
In the latest national data, US women of reproductive age are alarmingly heavy: 52% are overweight, 29% are obese, and 8% have a body mass index (BMI; in kg/m2) of ≥40, which places them in the obese III category (1). Those who are obese have difficulty conceiving (2), and complications during pregnancy and delivery are more common in obese than in normal-weight women (3-5). In addition, reproduction itself is associated with a net gain in weight. On average, weight retention postpartum is thought to be modest—1.3 kg at 10–18 mo after delivery in 1.59 million women in the 1988 National Maternal and Infant Health Survey (6)—but it is more generally estimated as ≈0.5 kg in US (7-9), Swedish (10), and British women (11). For individual women, however, pregnancy may be quite an important cause of weight gain (12). For example, Olson et al (13) found that 25% of the 540 women in their study experienced a major weight gain (≥4.55 kg) associated with pregnancy. Weight retention may be higher after first births than after higher-order births (14-16). Gestational weight gain (GWG) may contribute to complications during labor and delivery (4, 17), and it is an important determinant of postpartum weight retention (PPWR). In general, the more weight that women gain during pregnancy, the more weight that they retain afterward (18). Interventions to restrain GWG in the United States and elsewhere have not been uniformly successful in reducing PPWR (19-22). In fact, the proportion of US women who gain weight excessively during pregnancy is growing (23). In 2005, 20.6% gained >18.2 kg (40 lb) (24), the upper limit recommended by the Institute of Medicine (25) for women of any height.
Evidence is limited and conflicting about whether women who breastfeed their infants lose more weight than do women who do not breastfeed (25-27). Most of the women in those studies did not follow the current recommendations to exclusively breastfeed for 6 mo and then to continue breastfeeding for ≥6 more mo (28). Moreover, there is a reproducible, negative association between prepregnancy BMI and the duration of breastfeeding (29), and evidence is accumulating that obesity makes breastfeeding more difficult (30). Thus, it is possible that the lack of a consistent relation between breastfeeding and a reduction in PPWR has resulted from a combination of a pattern of breastfeeding that would not be expected to modify weight loss appreciably, low statistical power, or the poor quality of information about the intensity and duration of breastfeeding (or all 3 factors), as well as a complex association with prepregnancy BMI.
The prospectively collected data from the Danish National Birth Cohort (DNBC) provided a resource in which the association of breastfeeding and PPWR could be examined in a context of intense and sustained breastfeeding. We studied women from this large contemporary cohort and evaluated whether breastfeeding, which was reported in detail, modified the association among prepregnancy BMI, GWG, and PPWR at 6 and 18 mo postpartum.
INTRODUCTIONIn the latest national data, US women of reproductive age are alarmingly heavy: 52% are overweight, 29% are obese, and 8% have a body mass index (BMI; in kg/m2) of ≥40, which places them in the obese III category (1). Those who are obese have difficulty conceiving (2), and complications during pregnancy and delivery are more common in obese than in normal-weight women (3-5). In addition, reproduction itself is associated with a net gain in weight. On average, weight retention postpartum is thought to be modest—1.3 kg at 10–18 mo after delivery in 1.59 million women in the 1988 National Maternal and Infant Health Survey (6)—but it is more generally estimated as ≈0.5 kg in US (7-9), Swedish (10), and British women (11). For individual women, however, pregnancy may be quite an important cause of weight gain (12). For example, Olson et al (13) found that 25% of the 540 women in their study experienced a major weight gain (≥4.55 kg) associated with pregnancy. Weight retention may be higher after first births than after higher-order births (14-16). Gestational weight gain (GWG) may contribute to complications during labor and delivery (4, 17), and it is an important determinant of postpartum weight retention (PPWR). In general, the more weight that women gain during pregnancy, the more weight that they retain afterward (18). Interventions to restrain GWG in the United States and elsewhere have not been uniformly successful in reducing PPWR (19-22). In fact, the proportion of US women who gain weight excessively during pregnancy is growing (23). In 2005, 20.6% gained >18.2 kg (40 lb) (24), the upper limit recommended by the Institute of Medicine (25) for women of any height.Evidence is limited and conflicting about whether women who breastfeed their infants lose more weight than do women who do not breastfeed (25-27). Most of the women in those studies did not follow the current recommendations to exclusively breastfeed for 6 mo and then to continue breastfeeding for ≥6 more mo (28). Moreover, there is a reproducible, negative association between prepregnancy BMI and the duration of breastfeeding (29), and evidence is accumulating that obesity makes breastfeeding more difficult (30). Thus, it is possible that the lack of a consistent relation between breastfeeding and a reduction in PPWR has resulted from a combination of a pattern of breastfeeding that would not be expected to modify weight loss appreciably, low statistical power, or the poor quality of information about the intensity and duration of breastfeeding (or all 3 factors), as well as a complex association with prepregnancy BMI.The prospectively collected data from the Danish National Birth Cohort (DNBC) provided a resource in which the association of breastfeeding and PPWR could be examined in a context of intense and sustained breastfeeding. We studied women from this large contemporary cohort and evaluated whether breastfeeding, which was reported in detail, modified the association among prepregnancy BMI, GWG, and PPWR at 6 and 18 mo postpartum.
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