Smoking appears to boost the odds certain women will give birth to twins.

That’s the finding of a new study that shows African American mothers who smoke and have a specific genetic profile have a greater likelihood of delivering twins, Science Daily reports.

The research, published in the American Journal of Human Biology, indicates women who smoke who have a variant of the so-called “TP53” gene tend to have more twins, according to a team of researchers from the University of South Florida (USF) and the University of Illinois at Urbana-Champaign.

The findings, based on an analysis of 227 African American mothers, suggest smoking may somehow activate the gene in a way that boosts the odds of having twins.

"While smoking may have deleterious effects on fertility across many genotypes, in women of specific genotypes smoking may raise their odds of having twins," wrote the researchers. "Although we demonstrated that there are significant differences in [gene makeup] in mothers of twins compared to mothers of singletons, the most important difference between groups of mothers in our study is whether or not the mothers smoked."

The researchers also noted that because TP53 has implications for cancer, future research should investigate whether women with this particular gene mutation who have twins face greater breast cancer risks.