... a short sexual relationship duration is a significant risk factor for pre-eclampsia. A short duration was also assocaited with delivery of a small-for-gestational age (SGA) infant in ... women with abnormal Doppler findings during pregnancy.
Some researchers have previously proposed that an inappropriate maternal immune response to fetal antigens derived from paternal DNA plays an important role in pre-eclampsia pathogenesis. It has been suggested that an abnormal response results in restricted trophoblast invasion of spiral arteries – a characteristic of pre-eclampsia and, to some degree, SGA pregnancies.
This led to the hypothesis that the risk of pre-eclampsia is reduced by repeated prior exposure to semen from the biological father or by a longer pre-pregnancy duration of sexual relationship. This has been supported by the findings of some published studies ...
... The median length of sexual relationship with the biological father was 40 months in the pre-eclampsia group, 42 months in the SGA group, and 48 months in the control group.
... “a short duration of sexual relationship increases the risk of pre-eclampsia” and ... this is consistent with the hypothesis that a short pre-pregnancy duration is often insufficient for the development of maternal tolerance to paternal antigens.