Prevention of mother to child transmission of HIV

More than 2 million HIV infected women become pregnant each year, 90% of them in developing countries. Despite proven methods to prevent mother-to-child transmission, most of the infants delivered to these women receive no prophylactic intervention, resulting in infection and death of about 600,000 children per year. Prenatal HIV testing affords the best opportunity to prevent vertical transmission. Most health systems implement 1 out of 3 prenatal HIV testing approaches: the opt-in, opt-out and mandatory mother or neonatal HIV testing. The opt-out voluntary testing and the mandatory testing of newborns are associated with the highest testing rates. In high prevalence settings, a significant proportion of women decline for HIV on account of fear of social stigmatization and domestic violence.

Aining the results of the HIV testing is another matter that needs to be improved, particularly in developing countries. Studies indicate that 25% - 55% of pregnant women accepting HIV testing do not obtain their results and consequently do not receive same-day results. This increases the proportion of women who obtain HIV results thus maximizing perinatal HIV interventions.

Viral load, immune status, and the risk of HIV transmission

Factors associated with high risk of transmission include increased maternal plasma viral load, clinically or immunologically advanced HIV disease in the mother. It must be noted that transmission has been observed at viral load below the detection limit of the assay. Therefore, there is no safe viral load below which no transmission can be guaranteed. Because exposure to HIV in the maternal genital tract during delivery is a risk factor for vertical transmission, suppression of maternal viral load (plasma and genital) and improvement of immune status may be achieved by the use of HAART in pregnancy.

Cigarette smoking and illicit injection drugs have been shown to increase vertical HIV transmission. Obstetric factors potentially associated with increase rates of transmission include prolonged rupture of the membranes, clinical chorioamnionitis, episiotomy, scalp electrodes, forceps or vacuum extraction. Vertical transmission of HIV is reduced by more than 50% when elective caeserean delivery is performed.

The combination of elective caesarean delivery and antiretroviral therapy has reduced vertical transmission to fewer than 5% of deliveries.
 

Treatment regimens

The first trial to show that antiretroviral therapy can decrease vertical HIV transmission was the aids clinical trials group protocol 076(ACTG 076) study in 1994 that evaluated zidovudine. The rate of mother-to-child transmission was 25.5% in the placebo group and 8.3% in the zisovudine group. It is recommended that zidovudine be part of any combination antiretroviral regimen for PMTCT. The benefit  of zidovudine at reducing perinatal transmission is decreased if mothers breastfeed after delivery. Single dose nevireapine has also been reported to lower perinatal transmission rates. Currently, the standard of care is combination antiretroviral therapy, in cohort studies, transmission rates with HAART are lower than with zidovudine alone.

Mitochondrial toxicity in infants exposed to nucleoside reverse transcriptase inhibitors(NRTIs) during pregnancy has been of concern. It has however been reported that there is no significant association with the prevalence of congenital abnormalities or low birth weight. There is a need to monitor hepatic enzymes and electrolytes and to be vigilant to the symptoms of hepatic steatosis and acute lactic acidosis in women receiving NRTIs. Another potential risk to the mother is hyperglycemia, onset of exacerbation of diabetes mellitus, with the use of protease inhibitors.

There is a risk of drug resistance with zidovudine or nivirapine monotherapy. Use of the zidovudine/lamivudine combination has also been associated with development of lamivudine resistance. Development of lamivudine resistance. Development of resistance posses limitation to future therapeutic options. It is recommended to conduct resistance testing of maternal virus for all HIV infected pregnant women. The use of HAART leads to maximal virologic suppression, thus minimizing the risk of drug resistance.

-          DR. ADESINA