Abstract Body

HIV-infected women on ritonavir-boosted protease inhibitor (PI/r) based ART regimens in pregnancy may be at higher risk of preterm delivery (PTD, <37weeks gestation) but evidence is inconsistent.

We analyzed national surveillance data on HIV-infected women delivering a live-born singleton in the UK and Ireland between 2007 and 2015, who received antenatal ART. We excluded women who switched ART regimen in pregnancy; for women with repeat pregnancies we retained the most recent one. We compared PTD risk in pregnant women on NNRTI+2NRTI regimens, LPV/r+2NRTI regimens and other-PI/r+2NRTI regimens using multivariable logistic regression models. Analyses were adjusted for calendar year, maternal age, intravenous drug use (IDU) history, ART at conception and first antenatal CD4 count. After excluding women with a history of IDU we explored whether the association between regimen in pregnancy and PTD was modified by first antenatal CD4 count and consequently, stratified analyses by CD4 count (≤350cells/µl vs >350cells/µl).

Analyses included 1889 pregnant women on NNRTI+2NRTI, 2368 on LPV/r+2NRTI and 1816 on other PI/r+2NRTI; 10.4% and 3.8% of women delivered at <37weeks and <34weeks respectively. Overall, 3090 (50.9%) women conceived on ART; 105 (1.7%) women had an IDU history. Compared to women on NNRTI regimens women on LPV/r containing regimens were at higher risk of PTD (aOR 1.48, 95%CI 1.16, 1.88) but not those on other PI/r-based regimens (aOR 1.13 95%CI 0.89, 1.43). Increased PTD risk was also associated with first antenatal CD4≤350cells/µL (aOR 1.25 95%CI 1.03, 1.50), IDU history (aOR 1.80 95%CI 1.06, 3.07) and older age (>36years vs <28years) (aOR 1.30 95%CI 1.00, 1.67). After stratifying by first antenatal CD4 count (P interaction=0.0048), increased PTD risk in women on LPV/r compared to women on NNRTI was observed in those with CD4>350cells/µL but not in those with a lower CD4 count (see Table). In women with CD4≤350cells/µl conception on ART increased PTD risk whilst risk decreased with calendar year; no increased PTD risk in women on LPV/r (or other PI/r-based regimens) compared to women on NNRTI was observed.

In this national UK study pregnant women on LPV/r-based regimens but not on other PI/r-based regimens were at higher risk of PTD compared to pregnant women on NNRTI-based regimens but the association was only apparent in women with a higher CD4 count.