Using 30 years of longitudinal data from a nationally representative cohort of women, we study the association between breastfeeding duration and completed fertility, fertility expectations, and birth spacing. We find that women who breastfeed their first child for five months or longer are a distinct group. They have more children overall and higher odds of having three or more children rather than two, compared with women who breastfeed for shorter durations or not at all. Expected fertility is associated with initiating breastfeeding but not with how long mothers breastfeed. Thus, women who breastfeed longer do not differ significantly from other breastfeeding women in their early fertility expectations. Rather, across the life course, these women achieve and even exceed their earlier fertility expectations. Women who breastfeed for shorter durations (1–21 weeks) are more likely to fall short of their expected fertility than to achieve or exceed their expectations, and they are significantly less likely than women who breastfeed for longer durations (≥22 weeks) to exceed their expected fertility. In contrast, women who breastfeed longer are as likely to exceed as to achieve their earlier expectations, and the difference between their probability of falling short versus exceeding their fertility expectations is relatively small and at the boundary of statistical significance (p = .096). These differences in fertility are not explained by differences in personal and family resources, including family income or labor market attachment. Our findings suggest that breastfeeding duration may serve as a proxy for identifying a distinct approach to parenting. Women who breastfeed longer have reproductive patterns quite different than their socioeconomic position would predict. They both have more children and invest more time in those children.
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Breastfeeding can also elicit hormonal changes that increase mother-infant bonding (Uvnäs-Moberg and Eriksson 1996), which might increase future fertility.
We also used the NLSY sample-specific weights and obtained the same results.
Cumulative retention rates in the NLSY79 exceeded 90 % in 1993, when respondents were aged 28–36, and exceeded 80 % in 2000, when respondents were aged 35–43. With the military and poor white oversamples excluded, the sample includes 874 women who had no children. For 81 % of these women, the NLSY79 includes fairly complete information on their fertility. The remaining 19 % (n = 169) left the survey before year 2000. These 169 women were observed to a median age of 27, which represents approximately the 80th percentile of the age at first birth distribution for the sample. Only 9 % (n = 80) of the 874 women we categorize as not bearing children left the survey before age 27.
Although the minimum gap between this measure of early expected fertility and first birth is 2 years, the median gap is 7 years, and the interquartile range is 4–11 years.
Our alternative approaches included using the distribution quartiles rather than tertiles and dividing the categories into two alternative different intervals: 0, 1–8, 9–26, 27–52, 53–208 weeks and 0, 1–13, 14–26, 27–52, 53–208 weeks.
In this sample of almost 3,700 mothers, only 19 women breastfed for two years, and 11 breastfed beyond two years.
We omit from Fig. 2 the 11 women who breastfed beyond two years. Because not initiating (breastfeeding 0 weeks) is such a distinct and large group, we plot this mean directly from the data and use the polynomial smoother only for the remainder of the breastfeeding distribution shown (1 to 104 weeks).
Simply adjusting for race/ethnicity, and nothing else, makes this contrast significant as well.
In this subsample, women who breastfeed 22 weeks or longer have significantly higher average fertility than all other groups even without controls for any other characteristics. The categorical contrasts to women who do not initiate breastfeeding are also significant without controls, as are the contrasts for having three or more children (regressions not shown).
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We thank Doug McKee, Doug Miller, Berkay Ozcan, Kim Weeden, Kelly Musick, Peter Rich, and Rene Almeling for their suggestions and comments. We are especially indebted to Isadora Milanez for her extensive input and superb research assistance on this project.
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Maralani, V., Stabler, S. Intensive Parenting: Fertility and Breastfeeding Duration in the United States. Demography 55, 1681–1704 (2018). https://doi.org/10.1007/s13524-018-0710-7
- Child investment