High mother-to-child transmission risk

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There is a high risk of HIV seroconversion during pregnancy for women in South Africa, investigators report. The study involved approximately 10,000 mother and infant pairs and found that 3% of mothers became infected with HIV during pregnancy, accounting for over a quarter of all cases of mother-to-child transmission (MTCT) of HIV.

The authors believe their findings have important implications for prevention of mother-to-child transmission programmes in South Africa, and urge that women should have repeat screens for HIV infection after week 32 of pregnancy, during labour and again six weeks after giving birth. Women with HIV-positive partners and those undergoing screening for tuberculosis (TB) should also, the investigators recommend, be prioritised for HIV testing.

Current South African guidelines for the prevention of mother-to-child transmission of HIV recommend that women should be screened for HIV infection when first presenting to antenatal care, with retesting at week 32 of pregnancy and during labour. The aim is early identification of infections to allow interventions that can reduce the risk of mother-to-child transmission to below 1%.

Previous research has shown that many women continue to have an ongoing risk of infection with HIV during pregnancy. HIV viral load is very high during seroconversion, meaning that women infected with HIV during pregnancy could have a significant risk of transmitting HIV to their baby. A team of investigators therefore designed a population-based study to estimate the rate of HIV seroconversion during pregnancy after an antenatal HIV-negative test result, and the contribution of infection with HIV during pregnancy to early mother-to-child transmission risk.

The study involved 9,800 mother and infant pairs. The infants were aged between four and eight weeks. Infant dried blood spots were tested for HIV antibodies and DNA. The mothers’ medical records were reviewed, and they were also interviewed about possible HIV risk during pregnancy. Recruitment took place at 578 health facilities between August 2011 and March 2012. Approximately 30% of mothers had prevalent HIV infection and just over 3% seroconverted during pregnancy. The median time of seroconversion was week 33 of gestation, but in 28% of cases, seroconversion occurred after week 36.

HIV seroconversion during pregnancy was associated with a significant risk of early mother-to-child transmission. Approximately 11% of infants whose mothers seroconverted during pregnancy were infected with HIV; the rate of early mother-to-child transmission for mothers with prevalent HIV infection was 2%. Overall, mothers seroconverting during pregnancy represented 2% of all mothers and 7% of all mothers with HIV. However, they accounted for 26% of all cases of mother-to-child transmission of HIV.

Two-thirds of the women who seroconverted reported knowing the HIV status of their partner, with 2% stating their partner was HIV positive. The authors were concerned about the apparent “very low rates of HIV disclosure among sexually active couples,” and stress that World Health Organisation guidelines recommend offering counselling and testing to all pregnant women in prevention of mother-to-child transmission settings.

Screening for TB and having a HIV-positive partner were associated with a higher risk of seroconversion during pregnancy. Moreover, women who seroconverted were less likely than HIV-negative women to have had a doctor or nurse present when they gave birth.

“Our finding indicates that pregnant women have a high risk of acquiring HIV in pregnancy,” write the authors. “We believe provision of a package of both tuberculosis screening and HIV testing would improve early detection of both HIV infections, including incident infection, and tuberculosis infection.”

They recommend that priorities for prevention of mother-to-child transmission programmes in South Africa should include: repeat HIV testing at weeks 32 and 36 of gestation, at labour and six weeks postpartum; couples counselling and testing with early antiretroviral treatment (ART) for HIV-positive partners in serodiscordant relationships; and HIV testing and TB screening in antenatal care.

They conclude, “successfully implementing these interventions could help in early detection of incident HIV infection occurring during pregnancy, and early initiation of ART to reduce MTCT risk during pregnancy and breastfeeding.”

Aidsmap material
PLOS One abstract

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