How Birth Control Pills Affect Sexual, Marital Satisfaction

Good news and bad for women who take the pill: new research finds that those who meet their partners while taking oral contraceptives report less sexual satisfaction in their relationships — but they're also less likely to split up.

A study of 2,519 mothers, mainly from the U.S. and Czech Republic, found that those who met their first child's father while on the pill were less sexually satisfied with their men, less attracted to them and experienced greater sexual dissatisfaction over time, compared with women who weren't taking birth control pills.

But they also reported greater satisfaction with other aspects of their relationships, including the financial support provided by their mates, and were about 10% more likely to stay together. (If they did break up, the split was around 10% more likely to be initiated by the woman than the man.)

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So, how could the pill possibly affect mate choice? It comes down to chemistry.

The researchers had previously discovered that women's menstrual cycles affect the types of men to which they are most attracted. Part of having "chemistry" with someone is liking his smell, which is determined in part by an immune system molecule called MHC.

People tend to be attracted to partners with MHC types that are dissimilar from their own, probably because this would give their offspring a greater chance of survival by creating a diversified immune system. The pill, however, puts the body into a hormonal state similar to pregnancy — and pregnant women tend to prefer MHC scents that are similar to their own, probably because this would make them feel safe and comfortable around supportive relatives.

That means that if you're taking the pill, you may be more likely to find attractive men whose MHC is similar to your own — but during your regular cycle, these men might seem less your "type."

Indeed, during their most fertile phase, women tend to be drawn to more dominant, masculine men who are more likely to be unfaithful. In contrast, during the second part of their cycle, when they could already be pregnant, they are more attracted to calmer, more nurturing types.

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So, basically, meeting while on the pill might make you choose a "dad" who may not be the most exciting guy, but who will stick around and support the kids. Conversely, meeting while not taking hormonal contraceptives might make the bad-boy "cad" seem irresistible.

Of course, there are many, many variables involved in choosing a partner and the influence of taking the pill is not huge. It's possible that other underlying factors actually account for the differences between pill users and nonusers, perhaps related to their decisions about contraception and attitudes toward sex. The researchers tried to control for these factors, however, and still found that the effect persisted in two different countries.

Lead author Craig Roberts of the University of Stirling in the U.K. told the BBC: "Choosing a non-hormonal barrier method of contraception for a few months before getting married might be one way for a woman to check or reassure herself that she's still attracted to her partner."

My guess, however, is that if you are that concerned about your relationship, you might have other issues to iron out before booking the caterer.

The study was published in the Proceedings of the Royal Society B.

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Maia Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland's Facebook page and on Twitter at @TIMEHealthland.