New dads are more likely to feel less interested in sex when there is a newborn in the house because of increased tiredness or stress related to the new arrival, rather than because of anything to do with their partner, such as breastfeeding or postpartum vaginal issues, a new study has found.

Mothers who give birth also often experience a drop in sexual desire, usuallly for the same reasons, said Toronto-born researcher Dr. Sari van Anders of the University of Michigan in Ann Arbor.

"Our research demonstrated that co-parents report social, affiliative, and new-baby factors as stronger influences on their sexuality in the postpartum [period] than biomedical factors related to the birth itself — for example, hormones or lactation," she said.

The study, which was published online in The Journal of Sexual Medicine on Friday, notes that previous research on postpartum sexuality typically focuses on how pregnancy, birth and breastfeeding affect a mother's sexual desire. But little research has focused on how these changes affect her partner's shifts in sexuality.

The study sampled 114 partners (including 95 men and 18 women) of postpartum women. The respondents completed an online questionnaire about their sexuality during the three months following their youngest child's birth. Attention was paid to physical, social, psychological and relational experiences.

Emotional factors related to child care and personal intimacy mattered more when it came to sexual interest than any physical or hormonal changes endured by the birth mother, the survey revealed.

"Researchers have typically focused on birth mothers as a negative influence on their male partner's sexual desire, due to breast-feeding, lack of interest or postpartum vaginal issues," van Anders said. "In contrast to these assumptions, our empirical work demonstrated that co-parents — including men and women — experience low desire after childbirth because of fatigue, stress and [lack] of free time."

"All participants were able to report about high and low sexual desire, and almost all participants were re-engaging in the sexual activities they had engaged in before childbirth," she added. "Our results point to the need to look at a broader set of postpartum sexual experiences than just decreased desire or infrequent sex."