There were 82 new HIV infections
among the women studied, with an overall annual HIV incidence of 1.62%. (These
82 infections excluded ‘unlinked’ infections, i.e. ones coming from partners
other than the main partner.)
HIV incidence was significantly
raised during pregnancy and in the post-partum period. It was 1.25% a year in
women who were neither pregnant or post-partum, 3.75% in early pregnancy, 7.02%
in later pregnancy and 4.68% in the post-partum period. But because women had
the least sex in the post-partum period, the rate of infection during that
time was actually even higher than in pregnancy. The number of infections per
1000 sex acts was 1.05 for women not pregnant or post-partum, 2.19 in early
pregnancy, 2.97 in late pregnancy, and 4.18 post-partum.
In a multivariate analysis, these figures were then adjusted for the viral load of the partner, age
of the woman, PrEP and condom use.
Compared to a ‘reference’ case
of the risk seen in a non-pregnant, non-post-partum woman aged 25 not on PrEP whose
HIV-positive partner had a viral load of 10,000 copies/ml, the adjusted
relative risk of HIV transmission during pregnancy or post-partum was 2.76. In other words pregnancy or being post-partum magnified the risk of HIV infection nearly threefold, independent of other factors, and this was highly statistically significant (i.e. very unlikely to be a chance observation).
The relative risk compared with the reference case was 2.07 in early pregnancy, 2.82 in later pregnancy and 3.97 post-partum. Although in these subcategories, the confidence intervals were rather wide, they were still statistically significant and suggest the greatest risk of all – nearly four times normal – may come during lactation. This
increased risk was independent of the fact that sexual frequency and condomless
sex decreased as pregnancy progressed.
Presenter Renee Heffron said
that although obviously there were hormonal changes in women’s bodies during
pregnancy and lactation that probably explained the higher susceptibility to
HIV infection, more research was needed to establish the exact risk. The mechanisms may be similar to the
higher risk of HIV infection and transmission seen in women who use hormonal
contraceptives in some, but not all, studies. Heffron recommended
that women receive counselling about the substantially increased risk during
this period and that more research is needed to elucidate its cause.
Asked whether PrEP ought to be recommended for women during pregnancy and post-partum, Professor Wafaa El-Sadr of Columbia University's Mailman School of Public Health, chair of a press briefing on the study, commented that "maybe recommendations should say [PrEP] should be used given the very high risk in this population."