Background:  Hypertensive disorders of pregnancy are an important cause of maternal mortality in this environment, it accounts for about 20% of all maternal deaths in pregnancy in Nigeria.
Aim:  This study aims to determine the effect of the length of sexual cohabitation on the development of hypertension in pregnancy in a Nigerian population.
Materials and methods:  The study was a prospective cohort study; three centres were involved in the study between July 2006 and February 2009. For this study, the main outcome variable was the development of Hypertension in pregnancy. The main explanatory variable was the length of preconception sexual cohabitation. Univariate analysis was by t test, chi‐squared test and Fisher’s exact test for continuous and categorical variables. Multivariate analysis was by Cox hazard regression
Results:  In the study population, the incidence of gestational hypertension and pre‐eclampsia were 28.93% and 4.13% respectively, 29.64% had previous abortions and same paternity abortion rate was 25.92%. Length of sexual cohabitation before index pregnancy was protective against hypertension in pregnancy but not for pre‐eclampsia; there was a 4% decrease in the risk of developing hypertension for every month increase in cohabitation (hazard ratio, HR 0.96 (95% CI 0.93–0.99)). Also protective in this model was same paternity abortion with a HR of 0.71 (95% CI 0.55–0.93). A previous abortion was not protective (HR 1.05 (95% CI 0.82–1.35)).
Conclusion:  It was concluded that increased length of sexual cohabitation prior to conception reduces the risk of gestational hypertension.