Pregnant women who experience ongoing exposure to the baby's father's semen may be better protected against pre-eclampsia (pregnancy-induced hypertension) and having an underweight baby, report New Zealand researchers in the Journal of Reproductive Immunology.
To conduct the study, more than 2,500 first-time pregnant women were interviewed about the length of their relationship with the baby's biological father. The researchers found that when the pregnancies came to term, pre-eclampsia was less common in the women who had long-term sexual relations exclusively with the biological father, than in those who had multiple sexual partners.
Pre-eclampsia occurs because of a failure by the maternal immune system to down-regulate, or tolerate, its response to paternal antigens. "In normal pregnancies, prolonged exposure of the female immune system to paternal antigens following intercourse [could induce] tolerance of the maternal immune system to the paternal antigens," speculated Larry Chamley, from the University of Auckland. "Although the issue of whether prolonged semen exposure does protect against developing pre-eclampsia is not yet resolved, this paper seems to tip the weight of evidence back in favor of suggesting that prolonged semen exposure is protective."
The study also revealed that women who had undersized babies were also more likely to have been in shorter relationships, but only when 20 week ultrasounds demonstrated reduced blood flow to the fetus.
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Source: Journal of Reproductive Immunology