RESULTS
Among 500 participants, 436 (87%) had single, non-missing, live birth outcomes. We excluded 20 participants who experienced miscarriages, 11 who had stillbirths, seven with twin births, and 26 participants who were lost to follow-up (Figure 1 ). The distribution of miscarriages and stillbirths was similar across study arms. Baseline characteristics between the analytical sample and the 26 with missing outcome data were similar in terms of age, relationship status, education, income, HIV status, partner HIV status, primigravida, history of a preterm birth or low birth weight outcome, hypertension, nationality, and alcohol use. However, the standard-of-care group was more likely to have missing birth outcome data (8.7%) compared to the intervention group (2.6%). Our study team was able to contact 11 of the 26 participants missing birth outcome data by phone and determined that they were now living outside of Gaborone.
As seen in Table 1 , the median age in our analytical sample was 27 years, the median gestational age at first antenatal care visit was 17 weeks, about half of the participants were married or cohabiting, most women were citizens of Botswana, 7% had a recorded measure of hypertension, 17% were living with HIV, and the median number of antenatal care visits was six. Characteristics that differed statistically between intervention and standard-of-care arms included education level, income, citizenship, HIV status, first pregnancy, partner’s HIV status, clinic, and study period (p\(\leq\)0·05 for all).
The overall prevalence was 13.3% for the composite outcome of preterm birth and/or low birthweight, 9.4% for preterm birth, and 8.5% for low birthweight. Without controlling for potential group imbalance, the prevalence of preterm birth or low birthweight was not significantly different between the intervention (14%) and standard-of-care arms (13%).
Results from the multivariable logistic regression can be found inTable 2 . In all tested models, exposure to the intervention arm was associated with reduced odds of the composite outcome of preterm birth or low birthweight after controlling for primigravida, antenatal care visits, hypertension, and clinic site; however, the confidence intervals crossed one. Further, odds ratios were similar when limiting the sample to participants in cross-over clinics that received the intervention and standard-of-care assignment over time.
Using post-estimation analysis from the multivariable logistic regression model, the predicted prevalence of the composite outcome of preterm or low birth weight was higher in the standard-of-care (15%) group compared to the intervention group (11%) (Figure 2 ); however, the adjusted risk ratio (ARR) had confidence intervals that crossed one (ARR: 0.67; 95% CI: 0.38 to 1.17). Results were similar for preterm birth (ARR: 0.65; 95% CI: 0.33 to 1.28) and low birth weight (ARR: 0.57; 95% CI: 0.28 to 1.16).
In the posthoc analysis, the stratification reduced some of the differences between the intervention and standard of care groups. Among nulliparous participants, the groups were now balanced on nationality, HIV status, and time period; however, the groups continued to differ on education level, income, and partner’s HIV status. Although the HIV prevalence was 5% among nulliparous participants, 18% of participants said their partners were living with HIV and 29% did not know their partner’s status. In the multiparous group, the intervention and standard of care arms differed on income level, nationality, and partner HIV status. The HIV prevalence among multiparous women was 24%, and 20% reported that their partners were living with HIV and 31% did not know. Table 2 also provides results from the multivariable logistic regressions stratified by prior live birth. After controlling for hypertension and clinic, the intervention reduced the odds of the composite outcome, preterm and low birth weight, among the nulliparous group. However, no effect was found among multiparous women and the odds ratios switched directions.