Factors associated with preterm, early preterm and late preterm birth in Malawi

Assessment of risk factors for preterm birth in a population with high incidence of preterm birth and HIV infection.

Secondary analysis of data for 2,149 women included in a community based randomized placebo controlled trial for the prevention of preterm birth (APPLe trial (ISRCTN84023116) with gestational age at birth determined through ultrasound measurement in early pregnancy. Multivariate Logistic Regression analyses to obtain models for three outcome variables: all preterm, early preterm, and late preterm birth.

No statistical differences were noted for the prevalence of HIV infection (p = 0.30) or syphilis (p = 0.12) between women who delivered preterm versus term. BMI (Adjusted OR 0.91 (0.85-0.97); p = 0.005) and weight gain (Adjusted OR 0.89 (0.82-0.97); p = 0.006) had an independent, protective effect. Previous preterm birth doubled the odds of preterm birth (Adjusted OR 2.13 (1.198-3.80); p = 0.01). Persistent malaria (despite malaria prophylaxis) increased the risk of late preterm birth (Adjusted OR 1.99 (1.05-3.79); p = 0.04). Age <20 (Adjusted OR 1.73 (1.03-2.90); p = 0.04) and anemia (Adjusted OR 1.95 (1.08-3.52); p = 0.03) were associated with early preterm birth (<34 weeks).

Despite claims that HIV infection is an important cause of preterm birth in Africa, we found no evidence of an association in this population (unexposed to anti-retroviral treatment). Persistent malaria was associated with late preterm birth. Maternal undernourishment and anemia were independently associated with early preterm birth. The study did not assess whether the link was direct or whether a common precursor such as chronic infection was responsible for both maternal effects and early labour.