A population-based study of risk factors for adverse pregnancy outcomes in northern rural Iran : a follow-up from pre-pregnancy to delivery

Sammanfattning: There is a substantial lack of knowledge about adverse pregnancy outcomes and their risk factors in middle and low-income countries, including Iran. This thesis has endeavored to examine the association between maternal characteristics and risks of adverse pregnancy outcomes, using prospectively collected information from pre-pregnancy, antenatal visits and delivery records. Our specific objectives were as follows: to investigate the association between parental consanguinity (first cousin marriage) and the risk of stillbirth, to examine whether risk of stillbirth is influenced by decreasing maternal blood hemoglobin concentrations before and during pregnancy, and to study the effects of maternal opium use during pregnancy on risks of spontaneous or medically induced preterm birth and fetal growth restriction. As a secondary aim, we examined the prevalence of previously reported risk factors in the study population. This project was conducted in a rural part of the Golestan province in northern Iran which has a population of 1,700,000 (50% living in rural areas) where there are 17,000 registered pregnancies annually. The first study was restricted to singleton pregnancies who had received a pre-pregnancy visit. This case-control study consisted of 283 cases and 2,088 controls and was conducted to investigate the association between consanguinity and risk of stillbirth. The second study consisted of 495 singleton stillbirths (cases) and 2,888 singleton live births (controls). The third and fourth studies were population-based cohort studies, comprising a total of 920 opium users (“exposed”) and 920 non-opium users (“unexposed”) during pregnancy. In the first study, our findingsindicated that consanguinity was associated with an increased risk of preterm (<37 gestational weeks) stillbirth. The second study showed that compared with normal maternal hemoglobin concentration, high maternal hemoglobin concentrations (≥140 g/l) was associated with a more than twofold stillbirth risk. In addition, low maternal hemoglobin concentrations (<110 g/l) was associated with a reduction in stillbirth risk. The third study showed that compared with non-use of opium and tobacco, use of only opium during pregnancy was associated with an increased risk of preterm delivery and the risk was more than doubled among dual users of opium and tobacco. In the fourth study, a positive association was found between intrauterine opium exposure and risk of the birth of a Small for Gestational Age (SGA) infant. Among term births, opium use was also associated with short crown-heel length and small head circumference. These associations were slightly magnified for infants of dual user mothers. In conclusion, this project reported that consanguineous marriage was associated with an increased risk of preterm stillbirth. High hemoglobin levels and an absence of hemoglobin dilution during pregnancy could be considered as an indicator of a high risk pregnancy. Opium use during pregnancy had an association with a higher risk of preterm delivery. Infants of women who had used only opium had an increased risk of short crown-heel length and small head circumference at term birth. Opium use during pregnancy was also associated with a higher risk of Small for Gestational Age at birth.