Anemia and hypertension as risk factors for preterm delivery in Yerevan, Armenia

Abstract

Objective: Anemia and hypertension are the most common disorders among women delivering at Yerevan maternities. Their role as potential risk factors for preterm delivery was assessed. Design and Methods: A matched case-control study was conducted. Data were obtained from 5 maternities located at different sites, including the center of Yerevan. Approximately 2800 delivery records covering a six-month period (Sep 2002-Feb 2003) were reviewed. Women having a preterm delivery – less than 37 complete weeks of gestation at delivery – were defined as cases (n = 228). Women who delivered at term (37-41 weeks at delivery) and met the matching criteria were defined as controls (n =216). Age, parity, and first visit to antenatal care were used as matching criteria. In addition, both cases and controls were obtained from the same maternity to control for socioeconomic status (SES) and possible laboratory differences. They were matched also on season of delivery (autumn/winter). Anemia was defined according to WHO standards as Hb less than 11 g/dL. Hypertension was defined by a systolic blood pressure greater or equal to 140 mmHb and a diastolic blood pressure of greater or equal to 90 mmHb or by a rise in blood pressure of systolic ≥ 30 mmHg and diastolic ≥ 15 mmHg. Data analysis was performed using the Stata statistical package (v7.0). McNemar’s test was used for odds ratio calculation and conditional logistic regression was used to control for other potential confounders, such as multiple pregnancy, prior premature labor, and placental abruption. Results: The prevalence of anemia at the end of pregnancy was 42.5% in controls and 50% in cases; 15% of controls and 17.4% of cases had moderate anemia: Hb level 7.0-9.9 g/dl. There was only one case of severe anemia (Hb=6.8 g/dl), which was excluded from the analyses. There were no statistically significant differences in anemia prevalence at the end of pregnancy between cases and controls. The adjusted odds for preterm delivery in the presence of maternal anemia, defined as Hb less than or equal 9.0 g/dl, was three times higher as compared with the reference group of non-anemic women. However, the results were not statistically significant (95% CI = 0.9-10.6, p=0.067). The small number of observations with multiple pregnancy and prior preterm delivery precluded the inclusion of these variables in the final logistic regression model. After adjustment for potential confounders pregnancy induced hypertension (isolated hypertension, mild and severe preeclampsia) was positively associated with prematurity (adjusted odds ratio: 4.0; 95% CI = 1.9 to 8.7, p< 0.001). Chronic hypertension was also significantly different between cases and controls (adjusted odds ratio: 9.8, 95% CI= 1.2 to 80.5, p<0.05); however, the small number of observations with chronic hypertension resulted in a wide confidence interval. The adjusted variables were placenta abruption and premature rupture of membranes. Conclusion: Maternal anemia at the end of the third trimester of pregnancy was not significantly associated with prematurity. However, anemia with Hb level less than 9.0 g/dl increases the risk of preterm labor threefold. Pregnancy induced hypertension (isolated hypertension, mild and severe preeclampsia), as well as chronic hypertension were significantly associated with preterm delivery. However, future studies with larger sample sizes are required in order to investigate these relationships in the presence of potential confounders.