Maternal HIV infection and spontaneous versus provider-initiated preterm birth in an urban Zambian cohort.

Abstract

OBJECTIVE\nWe investigated the effect of maternal HIV and its treatment on spontaneous and provider-initiated preterm birth (PTB) in an urban African cohort.\n\n\nMETHODS\nThe Zambian Preterm Birth Prevention Study enrolled pregnant women at their first antenatal visit in Lusaka. Participants underwent ultrasound, laboratory testing, and clinical phenotyping of delivery outcomes. Key exposures were maternal HIV serostatus and timing of antiretroviral therapy (ART) initiation. We defined the primary outcome, PTB, as delivery between 16-37 weeks gestational age (GA), and differentiated spontaneous from provider-initiated parturition.\n\n\nRESULTS\nOf 1450 pregnant women enrolled, 350 (24%) had HIV. 1216 (84%) were retained at delivery, 3 of whom delivered <16 weeks. Of 181 (15%) preterm deliveries, 120 (66%) were spontaneous, 56 (31%) were provider-initiated, and 5 (3%) were unclassified. In standardized analyses using inverse probability weighting, maternal HIV increased the risk of spontaneous PTB (RR 1.68; 95% CI 1.12-2.52) but this effect was mitigated on overall PTB (RR 1.31; 95% CI 0.92-1.86) owing to a protective effect against provider-initiated PTB. HIV reduced the risk of preeclampsia (RR 0.32; 95% CI 0.11-0.91), which strongly predicted provider-initiated PTB (RR 17.92; 95% CI 8.13-39.53). The timing of ART start did not affect the relationship between HIV and PTB.\n\n\nCONCLUSION\nThe risk of HIV on spontaneous PTB appears to be opposed by a protective effect of HIV on provider-initiated PTB. These findings support an inflammatory mechanism underlying HIV-related PTB and suggest that published estimates of PTB risk overall underestimate the risk of spontaneous PTB.