Of the 221 pregnant women at 11 participating HIV centres who initiated cART during the index pregnancy and had sufficient data for analysis, 192 had a detectable pVL after 14 days therapy. 29 women had VL1 <50 copies/mL and are described separately.
Baseline characteristics of the 192 women included in the main analysis are described in Table 1. 83.3% were Black African/ Caribbean, 98.5% identified heterosexual intercourse as their route of HIV acquisition, 63.5% were cART-naïve and median CD4+ count prior to initiating cART (baseline) was 339 cells/µL (Table 1). 126 (65.6%) had pre-cART (baseline) plasma HIV RNA <30,000 copies/mL, 37 (19.3%) between 30,000 – 100,000 HIV RNA copies/mL and 29 (15.1%) had baseline plasma HIV RNA >100,000 copies/mL. 91% of women commenced cART before 28 weeks’ gestation: 181 (94.3%) women initiated a dual NRTI backbone plus a third agent, 11 (5.7%) initiated abacavir, lamivudine and zidovudine (ABC/3TC/AZT) (Table 1) and seven (3.6%) initiated quadruple cART. Amongst the 192 women included in the main analysis, pVL fell by a median of 1.8 log10 HIV RNA copies/mL 14 days after initiating cART, and median T/2 was 2.5 days (Table 1).
Factors associated with first-phase plasma HIV RNA half-life decay
Univariate linear regression analysis demonstrated that lower baseline CD4+ T-cell count, higher VLBL and INSTI-based cART were associated with faster viral decay (shorter T/2) (Table 2). However, in multivariable regression analysis, only higher VLBL remained independently associated with shorter T/2 (-0.61 days per 1 log10 plasma HIV RNA higher, p<0.001) (Table 2).
Factors associated with having an undetectable maternal plasma viral load at 36 weeks’ gestation
In multivariate logistic regression analysis, the following factors were associated with a higher probability of having an undetectable maternal pVL by 36 weeks’ gestation: lower maternal pVL 14 days after initiating cART (odds ratio (OR) 0.05, 95% confidence interval (CI) 0.01, 0.19) and earlier gestational age when cART was initiated (OR 0.66, 95% CI 0.58, 0.76) (Table 3).
Differences in HIV- and obstetric-related parameters when stratified according to antiretroviral third agent class
T/2 was significantly shorter in women commenced on INSTIs compared to those commenced on PIs, non-nucleoside reverse transcriptase inhibitor (NNRTIs), and ABC/3TC/AZT (p <0.001, p <0.001 and p=0.03, respectively) (Table 4). T/2 was significantly longer in women commenced on PIs compared to NNRTIs, p=0.03 (Table 4).
Women who initiated an INSTI had significantly higher VLBL compared to women initiating PIs and ABC/3TC/AZT (p<0.001 and p<0.001, respectively), while women commenced on ABC/3TC/AZT had significantly lower VLBL and higher baseline CD4+ counts compared to women commenced on PIs and NNRTIs (Table 4). Women who initiated NNRTIs had lower baseline CD4 compared to women initiated on PIs. While there was no statistically significant difference in the gestational age at which cART was commenced when stratified according to the three third agent antiretroviral classes and ABC/3TC/AZT (Table 4), higher VLBL was significantly associated with earlier gestational age when cART was initiated, p = 0.02.
Between the four groups, the overall time to an undetectable pVL was numerically shorter in women commenced on INSTIs, but statistically only approached significance when comparing women initiating INSTIs (27.5 days) and NNRTIs (51.5 days), p=0.05 (Table 4).
An undetectable pVL was seen in 72.9% of all women by 36 weeks gestational age with broadly similar rates across the three antiretroviral third agent classes: PIs 72.0%, NNRTIs 65.6% and INSTIs 76.5% (Table 4). 164 (85.4%) women had an undetectable pVL by delivery: PIs 85.6%, NNRTIs 75.0% and INSTIs 94.1% (Table 4). All women who initiated ABC/3TC/AZT had undetectable pVL at both 36 weeks’ gestation and delivery. Statistically, the proportions of women with undetectable pVL at 36 weeks’ gestation and at delivery did not differ significantly by antiretroviral third agent class (p=0.13 and p=0.17, respectively).
Women with pVL <50 copies/mL at day 14 following cART initiation
Baseline characteristics for the 29 women with VL1 <50 copies/mL were broadly similar to the 192 women included in the main analysis (Table 1). However, this cohort of 29 women had significantly higher baseline CD4+ count (p = 0.001), lower VLBL (p < 0.001), a higher proportion with Hepatitis B co-infection (p = 0.007), and all women had VLBL <30,000 copies/mL. The longest estimated T/2 in this cohort of 29 women was similar to the T/2 seen in the subgroup of women included in the main analysis with VLBL <30,000 copies/mL, p = 0.354.
Infant HIV infection rates
Infant HIV infection status was established for 171/221. All 171/221 infants were negative by molecular HIV testing at birth. For the remaining 50/221, infection status was not available. Although data on infant HIV peri-exposure prophylaxis were not available, each centre managed infants according to the contemporaneous version of the BHIVA guidelines on the management of HIV infection in pregnancy.