Risk of Female HIV Acquisition Per Sex Act Increases During Pregnancy

Recent research presented at CROI 2018 finds that the risk of female HIV acquisition per sex act steadily increased through pregnancy and was highest during postpartum.

In several settings where HIV prevalence is high, fertility rates are also high. Some past research has indicated significantly higher HIV incidence during pregnancy.

At 25th Conference on Retroviruses and Opportunistic Infections (CROI), Renee Heffron, PhD, MPH, assistant professor at the University of Washington presented study results that suggested that a woman’s risk of acquiring HIV through sexual intercourse with an HIV-infected male partner increases during pregnancy, with risk being highest during the postpartum period.

“Our findings suggest that biological changes during pregnancy and postpartum may increase HIV risk,” Dr. Heffron said in a press conference at CROI. “This finding has a number of important public health implications. We have tremendous opportunities in antenatal and postnatal care, to promote HIV prevention and care.”

The risk of transmission was observed per sex act, even after accounting for sexual behavior, PrEP, and HIV viral load. Per sex act analyses provide an understanding of absolute and relative risks of HIV transmission; this also sheds light on whether or not increased risk during pregnancy and postpartum can be attributed to biological or sexual changes.

HIV infections that occur during pregnancy or postpartum, not only have negative consequences on women but carry the risk of perinatal HIV transmission to the fetus or newborn through breastfeeding.

The study involved 2751 African serodiscordant couples, enrolling in either of 2 HIV prevention clinical trials: the Partners PrEP Study and the Partners in Prevention HSV/HIV Transmission Study.

HIV uninfected female partners were followed prospectively for ≤48 months to undergo HIV and pregnancy testing either monthly or quarterly, depending on the trial. Sexual frequency and condom use were reported on a monthly basis.

The study time was categorized by reproductive stage as early pregnancy, late pregnancy up to 6 months postpartum or non-pregnant. Researchers utilized a complementary log-log model comparing the probability of male-to-female HIV transmission per sex act by reproductive stage.

Overall, the pregnancy incidence was 12.50 per 100 woman-years (95% CI: 11.52-13.55) and out of the 686 pregnancies that occurred, there were 82 HIV transmissions events.

When determining transmission probabilities per sex act, differences between couples regarding condom use, PrEP use, age, and the male partner’s HIV viral load were considered.

Researchers established that the reference case for HIV transmission probability is a condomless sex act between a 25-year-old woman not using PrEP and a male partner with HIV RNA of 10,000 copies/ml.

A probability was calculated of 1.05 HIV transmissions per 1000 sex acts when the woman was not pregnant, and 2.19 transmissions per 1000 sex acts during the first 13 weeks of pregnancy.

After researchers adjusted for condom use, age, use of PrEP and HIV viral load, the probability of transmission per sex act was significantly higher in late pregnancy (14 weeks to delivery) rising slightly to 2.97 per sex 1000 sex acts, increasing further to 4.18 HIV transmissions per 1000 sex acts for the first 6 postpartum months.

Findings underscore the importance of expanding HIV prevention and testing services for pregnant and postpartum women to prevent sexual transmission and identify acute HIV infections in those living in areas with high HIV prevalence.

“Our data highlight the importance of counseling women on increased risk throughout pregnancy and postpartum, promoting maternal repeat HIV testing, identifying and linking HIV infected partners to ART and care and promoting HIV prevention strategies that women can control themselves without the need of a partner such as oral PrEP during pregnancy and postpartum,” Dr. Heffron stressed.

Currently, the World Health Organization (WHO) recommends including HIV testing as part of a routine component of antenatal, childbirth and postpartum care to couples and partners.

The risk of HIV transmission per sex act steadily increased through pregnancy, with the highest risk occurring during postpartum, suggesting that biological changes during these periods increase the risk.

Researchers note that it’s critical to understand the factors that affect HIV acquisition risk during and after pregnancy, in order to ensure that women are equipped with the best preventive tools.

While further research is needed to better understand biological susceptibility, HIV prevention and testing in antenatal and postpartum care in high-risk settings is warranted to prevent sexual transmission and to identify acute maternal HIV infections, Dr. Heffron concluded.

A previous version of this article can be found on MDMagazine.com.