The effect of STI screening during pregnancy on vertical transmission of HIV and adverse pregnancy outcomes in South Africa: a modelling study

Introduction

Sexually transmitted infections (STIs) in pregnancy are associated with an increased risk of vertical HIV transmission and adverse pregnancy and birth outcomes. In South Africa, syndromic management is the standard of care for STI management. We assessed the potential impact of point-of-care (POC) screening for curable STIs (Chlamydia trachomatis [CT], Trichomonas vaginalis [TV] and Neisseria gonorrhoeae [NG]) during pregnancy on vertical HIV transmission and adverse pregnancy and birth outcomes.

Method

We developed a static mathematical model to estimate the impact of syndromic management compared to POC screening of STIs in pregnant women attending antenatal clinics in South Africa over one calendar year (2022). Our model assumptions regarding the effect of CT, NG and TV on adverse pregnancy/birth outcomes and vertical HIV transmission were informed by two separate meta-analyses that we conducted. Local studies informed estimates of STI prevalence, POC screening uptake and treatment, and sensitivity of syndromic management.

Results

In the absence of POC screening for curable STIs, 25.5% of pregnant women without HIV and 34.6% of pregnant women living with HIV were estimated to have undiagnosed and untreated STIs. In the POC scenario, 92% (95% CI: 85−100%) of STIs were diagnosed and treated during pregnancy, reducing antenatal maternal HIV incidence by 10.0% (95% CI: 1.0−20.1%). Overall, vertical HIV transmission was anticipated to reduce by 8.6% (5.2−13.8%), with reductions of 20.9% (15.2−27.0%) at birth and 2.5% (−0.9% to 9.0%) postnatally, in the POC screening scenario compared to current syndromic management. POC screening of curable STIs is further estimated to reduce the incidence of stillbirth by 10.1% (1.3–18.7%), preterm delivery by 6.3% (3.4–9.7%), infants born small for gestational age by 2.7% (0.7–4.9%) and low birth weight by 9.1% (0.9–18%).

Conclusions

POC STI screening and treatment may modestly reduce maternal HIV incidence, vertical HIV transmission, and the risk of adverse pregnancy and birth outcomes, and would substantially reduce the burden of curable STIs in pregnancy. The study provides evidence to move beyond the syndromic management of STIs in South Africa, particularly in antenatal care.