Primary Exposure and Covariates
Our primary exposure was assignment to either the intervention or standard of-care-arms of the study. Covariates of interest were factors found to be associated with preterm birth(14) or low birth weight(15) in previous research that could be imbalanced between the arms. Initial covariates examined were age (≤25 years vs above 25 years), relationship status (married/cohabitating vs not), education level (primary level or less vs secondary level or higher), income (≤2000, >2000 Pula (~USD 160)/month, or unknown), nationality (Motswana vs other), HIV status (positive vs negative), partner’s HIV status (positive, negative, or unknown), parity (prior live birth vs not), recorded history of prior preterm or low birth weight outcome among normal singleton births (ever had a preterm birth or low birth weight infant vs. no history of preterm or low birth weight births among normal singleton births), treatment for STI symptoms between the first and second study visits (STI treatment included azithromycin, erythromycin, ceftriaxone, doxycycline, and metronidazole), proportion of WHO recommended antenatal care visits achieved by gestational age at delivery,(16) delivery mode (spontaneous vaginal delivery vs other), and hypertension during pregnancy (defined as either a systolic pressure of ≥140 mmHg or diastolic pressure of ≥90 mmHg recorded at first antenatal care visit or during the third trimester. We also examined any hypertension vs none, as well as through a three-category variable: “early” hypertension at or before 20 weeks, “late” hypertension after 20 weeks, or no hypertension), alcohol use during pregnancy (using the Alcohol use Disorders Identification Test (AUDIT-C) of any use (AUDIT-C score>0) vs none and harmful use (AUDIT-C score≥3) vs none and non-harmful),(17) any tobacco use during pregnancy, clinic site where care was received, and enrollment period (Feb 2021-Jan 2022 vs Feb 2022-Dec 2022).