Women who breastfeed their first child for five months or longer are more likely to have three or more children, and less likely to have only one child, than women who breastfeed for shorter durations or not at all.

In “Intensive Parenting: Fertility and Breastfeeding Duration in the United States,” published in the journal Demography Sept. 19, co-authors Vida Maralani and Samuel Stabler (Hunter College) report that women who breastfed did not differ in how many children they expected to have before they started their families. Rather, the number of children women actually bear differs by how long they breastfeed their first child. Women who breastfeed for shorter durations are more likely to have fewer children than they expected than to have more children than expected. In contrast, women who breastfeed longer are as likely to achieve their expectations as to exceed them, and they are nearly as likely to have more children than they expected as they are to have fewer.

The researchers caution that their results do not imply that breastfeeding duration causes women to have larger families. They write, “Indeed, our study reveals the opposite: the interconnectedness of family preferences and child investment across the life course.” But they do find that many factors, such as differences in education, marital status, family income, and working for pay do not explain these patterns. The authors point to the need to study other potential explanations such as spousal support, preferences for time spent with children or work flexibility.

“Breastfeeding is a time-intensive and culturally and emotionally charged topic in the U.S. with many different stakeholders,” said Maralani, associate professor of sociology. “Women hear the strong message that they should breastfeed their infants for the first year of life, yet it is unambiguously clear that they find these guidelines difficult to follow in practice. Many report feeling shame and disappointment about nursing for shorter durations or supplementing with formula.” The authors wanted to explore how breastfeeding duration was associated with how many children women go on to have.

The researchers used a nationally representative longitudinal dataset, from 1979 to 2012, which provides information on a cohort of nearly 3,700 mothers. They measured women’s expected fertility at least one year before women conceived their first children to examine the link between their expectations of their future fertility and their actual behavior. These data also enabled the authors to account for differences in breastfeeding and fertility by education, age, marital status, family income and work histories.

Maralani and Stabler’s findings are in stark contrast to established research that shows highly educated Americans are more likely to have fewer children than they expected. Instead, the researchers write, “long-duration breastfeeding serves as a proxy for identifying a group of very highly educated women who seem to achieve and exceed their expected fertility across the life course ... our results suggest that breastfeeding duration may serve as a powerful proxy that captures numerous observed and unobserved preferences about family and child investment, and necessarily, the tradeoffs that women and couples make.”

Linda B. Glaser is a staff writer for the College of Arts and Sciences.