Effect of iron supplementation during early pregnancy on the development of gestational hypertension and pre-eclampsia.

OBJECTIVE: To investigate the association between iron supplementation during early pregnancy and the presence of de novo hypertension after 20 weeks' gestation (either gestational hypertension or pre-eclampsia).

STUDY DESIGN: Retrospective cohort study.

METHODS: This study retrospectively reviewed the medical records of non-anemic pregnant women who received first antenatal care at the Department of Obstetrics and Gynecology, Faculty of Medicine Vajira Hospital, Navamindradhiraj University, Bangkok, Thailand, during the June 2009-December 2010 study period. All included women had blood pressure and urine albumin level data that were recorded at each antenatal visit. The study population was divided into one of the two following groups: iron supplementation starting at gestational age (GA) < 16 weeks (study group) or GA ≥ 16 weeks (control group). A comparison of the proportion of de novo hypertension arising after 20 weeks' gestation was then performed between groups.

RESULTS: Four hundred non-anemic pregnant women were included, with 200 patients allocated to each groups. The overall incidence of de novo hypertension after 20 weeks' gestation was 10% (40/400), with significantly higher prevalence in the study group than that in the control group [13.5% (27/200) vs. 6.5% (13/200); relative risk: 2.14, 95%, CI 1.22-3.73; p = 0.008]. None of the women in this study developed anemia at time of delivery. There was no significant difference between groups for GA at delivery, birth weight, or birth asphyxia.

CONCLUSION: In our study population, iron supplementation before 16 weeks' GA was significantly associated with increased risk of developing de novo hypertension after 20 weeks' gestation.