Mid-pregnancy or “shotgun” unions with the child’s father fared best, post-birth unions with the father were less likely to last, and unions with a new partner faced the highest dissolution risk of all.

The share of marriages and cohabiting relationships that appear to be prompted by conception is rising. What are the odds that these types of relationships will last?

It’s common knowledge that shotgun marriages have declined in prevalence since the mid-twentieth century. Yet seemingly paradoxically, the share of marriages and cohabiting relationships that appear to be prompted by conception is rising. And these days, some couples conceive a child together, give birth, and only later combine households or marry. What are the odds that these types of relationships will last?

Bowling Green sociologist Karen Benjamin Guzzo examined that question recently in the Journal of Marriage and Family. Using the 1997 cohort of the National Longitudinal Survey of Youth, which follows thousands of Americans born between 1980 and 1984, Guzzo compared the break-up risk of various groups of women who became pregnant outside a co-residential relationship. (Marriages and cohabiting relationships are together classified as “co-residential unions,” or “unions” for short, and the study focused only on conceptions leading to a woman’s first live birth, ending with 2011 data.) These women were generally younger, more socioeconomically disadvantaged, and more likely to come from single-parent families than the average American mother.

Guzzo placed the women in her sample in three categories: those who formed a union with their child’s father during pregnancy, those who formed a union with him at some point after birth, and those who formed a union with a new partner, whether during pregnancy or after birth.

Her analysis revealed the pattern that you might have predicted. Mid-pregnancy or “shotgun” unions with the child’s father fared best, post-birth unions with the father were less likely to last, and unions with a new partner faced the highest dissolution risk of all. In an analytical model controlling for mothers’ socioeconomic and demographic traits, new-partner unions were almost three times as likely to dissolve during the study period as mid-pregnancy unions with the father of the child. The relationships of mothers who had lived with both their parents during adolescence were more likely to last than those of mothers with other backgrounds, but women’s personal socioeconomic traits were not linked to their odds of breaking up with partners. And marriages proved more stable than cohabiting relationships. Specifically, in Guzzo’s words, “The odds of dissolution were more than tripled among continuously cohabiting unions than direct marriages, but cohabiting unions that transitioned to marriage did not exhibit higher dissolution risks” than marriages not preceded by cohabitation.

Unsurprisingly, women in the NLSY survey sample whose first pregnancy began within a co-residential relationship were less prone to relationship dissolution than women who formed mid-pregnancy unions, confirming earlier research on the subject, but this was only the case if union type was not considered. For women in a union at birth, the type of union—cohabitation vs. marriage—was more important than when that union began (relative to conception) in determining break-up risk.

In explaining her findings, Guzzo emphasized the role of selection, noting “it seems that the most committed and stable couples are selected into coresidence prior to birth.” In other words, it is likely couples’ pre-existing relationship quality and mutual dedication, rather than the timing of their co-residential unions as such, that explains the apparent advantage of combining households before birth or conception. In the case of new-partner unions, which exhibited particularly high rates of instability, couples “may face boundary ambiguity, jealousy, and competing obligations across families and households” of the sort that many stepfamilies confront.

The implications for single people without kids are clear. As readers of this blog need hardly be reminded, it is crucial to decide in relationships, rather than slide through them, to use Scott Stanley’s terminology. Moving in with a new partner because of external factors, such as someone’s lease running out or a surprise pregnancy, is more likely to end poorly than a union that couples enter because they have chosen to publicly express their long-term commitment to one another. Thus, as Stanley advises, single people who hope to marry and have kids someday should try to take it slow in relationships and proceed deliberately from one step of a relationship to the next.

The takeaway for couples who find themselves expecting their first child outside of marriage or cohabitation is less clear, as so much depends on their particular circumstances. When the relationship is strong and no red flags are present, these couples should consider marrying, and not only for the sake of their child. Their relationships definitely face tough odds, but if this new study and prior research on the experiences of single parents and stepfamilies are correct, these couples may already be looking at their best chance for a lasting union.

Anna Sutherland is a writer and editor living in Michigan.