Objectives To confirm the protective effect of pre-conceptional cohabitation and same paternity early pregnancy losses on pregnancy induced hypertension in a population of nulliparous pregnant women, which may then afford an opportunity to design primary preventive family planning programs for hypertension in pregnancy. Methodology This was an observational cohort study with a nested case control component involving 646 nulliparous pregnant women attending antenatal care at the University College hospital Ibadan. A structured questionnaire was administered at recruitment. Urinalysis and blood pressure measurement were taken at recruitment and subsequent visits. The main outcome measure was the development of hypertension in pregnancy (binary) and the main exposure measure was the length of pre-conceptional cohabitation. Logistic and Cox regression models was utilized in the data analysis.