Washington, Nov 13 Remain faithful if you want healthier babies, that's the conclusion of a new study.

Faculty of 1000 reviewers examined a study from New Zealand on whether prolonged exposure to the father's semen protects new mothers against pre-eclampsia and having an undersized baby

In the study by Kho and colleagues at the University of Auckland, published in the Journal of Reproductive Immunology, 2507 first-time pregnant women were interviewed about the length of their relationship with the baby's biological father.

When the pregnancies came to term, pre-eclampsia (pregnancy-induced hypertension) was found to be less common in women who had long-term sexual relations exclusively with the biological father, than in those who had been with their partner only for a short time (i.e. less than six months).

The study also revealed that women who had undersized babies (SGA, or 'small for gestational age') were also more likely to have been in shorter relationships, but only when 20 week ultrasounds demonstrated reduced blood flow to the fetus.

F1000 reviewer Dr Larry Chamley explains that "in normal pregnancies ... prolonged exposure of the female immune system to paternal antigens following intercourse (without barrier contraception) [could induce] tolerance of the maternal immune system to the paternal antigens.

"But the exaggerated maternal inflammatory response in pre-eclampsia is due to a failure of the maternal immune system to down-regulate or tolerate its response to paternal antigens." (ANI)