The results of this review indicate, as other reviews have suggested,8
that women who are overweight or obese have increased reduced rates of BF initiation and earlier termination. In contrast to previous reviews, however, this review suggests that these relationships need to be further clarified, particularly in relationship to race/ethnicity and medical complications, such as diabetes mellitus. As some studies found obesity differentially impacts African American women with less risk for failure to initiate and terminate BF in comparison with white and Latina women, it is important to further clarify if these differences might be attributed to sociocultural, environmental, or physiological factors.
Additionally, future studies should evaluate the role that medical complications, particularly gestational diabetes, may play in impacting BF initiation and duration patterns. The 1 study18
reviewed here that evaluated an interactive effect of medical/labor complications did not find an independent effect of maternal overweight/obesity on BF initiation or duration; only obese women with medical/labor complications had increased risk for failure to initiate BF and greater risk of stopping BF. The other studies reviewed here either excluded women with gestational diabetes mellitus or did not assess the possible role of diabetes in BF patterns.
Clinical and physiological data with women with diabetes mellitus suggest possible hormonal reasons for delayed lactogenesis, including a reduced amont of circulating human placental lactogen, which is positively correlated with breast growth in pregnancy.27
A recent study found that term infants born to mothers with gestational diabetes mellitus treated with insulin had poorer sucking patterns compared to infants of mothers without diabetes, suggesting a newborn's neurological behavior may be affected by maternal diabetes28
and emphasizing the importance of evaluating maternal diabetes in any study that assesses the association between maternal obesity and BF success. Studies from experimental animal models suggest that maternal obesity is associated with different types of metabolic derangements, including a higher insulin response and slower glucose disposal rates, as well as higher fasting insulin concentrations.15
These changes might be especially pronounced in women who have diabetes that is poorly managed. Other studies have cited the fact that there may be a reduced fall in progesterone (which triggers lactogenesis) during the postpartum period in overweight/obese mothers because progesterone is produced in adipose tissue, although this hypothesis has yet to be proven.16
The role of extreme maternal BMI category, specifically women who have a BMI ≥35 or ≥40, should be further evaluated in future studies, particularly given the rising percentage of women in the United States and internationally who fall into this category.29
Biological data suggest that adipose tissue changes as obesity becomes more severe, with histological changes as well as changes in endocrine and paracrine secretion.30
In the studies reviewed, obese and, in some cases, extremely obese women were more likely to have failure to initiate BF or reduced duration of BF in comparison with overweight or normal weight women. The study by Baker et al.25
found increasingly higher relative risks for higher classes of obesity, as did Liu et al.,21
who also found that only extremely obese women (BMI≥35) were more likely to fail to initiate BF.
Future studies should investigate the role of gestational weight gain and the differential impact it may have on women of different BMI categories on BF outcomes. Excess maternal adiposity may interfere with the development of mammary glands at various times (before conception, during pregnancy, and during lactation), although limited data are available on how timing of adiposity gain could impact BF outcomes.30
Some previous studies not included in this review used postpartum BMI,31,32
potentially conflating the relationship between maternal BMI category (prepregnancy) and gestational weight gain on BF outcomes. One study evaluated in this review conducted a stratified analysis for gestational weigh gain, finding important differences based on BMI category in risk for failure to initiate BF19
; another analyzed gestational weight gain in a separate model because it was so closely correlated with maternal BMI category.22
In the study by Li et al.,20
of underweight and normal weight women, the odds of never initiating BF were lower the greater the gestational weight gain, whereas no such relationship was observed in overweight and obese women. Similarly, gaining less than the recommended weight gain during pregnancy increased the odds of failure to initiate BF in all but the obese women. There may be important factors associated with adiposity gained in pregnancy that could impact lactogenesis and BF rates, in contrast with adiposity that was present before pregnancy; future studies should investigate these possible differences.
Few studies reviewed evaluated the role of maternal behavioral factors on BF success except for the study by Hilson et al.,16
which comprehensively evaluated BF knowledge and behaviors via survey and observational analysis before hospital discharge. As previous reviews and studies indicate, there are likely behavioral factors that contribute to reduced BF initiation and duration in overweight and obese women, including the choice to breastfeed,30
in addition to the biological or mechanical factors. To better understand the relative contribution of social and psychological factors vs. biological or mechanical factors, future studies must evaluate all these potential pathways to poor BF outcomes.