Severity of Maternal HIV Disease and Adverse Birth Outcomes
Severity of Maternal HIV Disease and Adverse Birth Outcomes
In this secondary analysis of a large cohort of HIV-infected pregnant women who delivered a live singleton infant in Malawi between 2000 and 2004, we tested the hypothesis that severity of HIV-1 infection is associated with risk of LBW or PTD. This cohort is unique because all women were infected with HIV-1 subtype C, were antiretroviral treatment naive, were rigorously tested for malaria, and were normotensive. This study was not designed to comprehensively determine significant predictors of LBW or PTD in HIV-infected women; rather, it was designed to characterize the independent associations between 3 specific measures of HIV-1 disease severity, LBW, and PTD, adjusting for factors that confounded or modified those associations. Although our malaria-positive sample size was small, HIV-1 severity in this group appeared not to be associated with adverse birth outcomes. However in malaria-negative women, maternal HIV-1 disease severity was significantly associated with increased prevalence of LBW and PTD. This association persisted in multivariate models adjusted for residence, primigravid status, maternal education, and maternal anemia, and the result was also robust to several sensitivity analyses, including exclusion of PTD, exclusion of infants who became HIV infected in utero, and stratification by mode of malaria diagnosis.
The average peripheral viral load of participants in this study, all of whom were antiretroviral treatment naive, was approximately 32,000 copies per milliliter. The adjusted PR for LBW corresponding to a 3-log increase in viral load among women without malaria is 2.82 (95% CI: 1.32 to 6.07), meaning that women with average viral loads have 3 times the prevalence of LBW as women with an undetectable viral load. Administration of antiretroviral therapy (ART) that reduces viral load to an undetectable limit could lead to extremely significant relative reductions in LBW among malaria-negative Malawian women.
An association between maternal HIV-1 infection and LBW has been previously observed, including several studies in Malawi. In a meta-analysis of 6 cohorts of HIV-infected Malawian women, 13% of the infants born to HIV-infected women had LBW, although malaria status was not reported. In this study, 21% of the infants born to HIV-infected women were LBW, more than double the 8% prevalence of LBW among HIV-negative women in the MHP cohort (Jess Kwiek, PhD, 2013, unpublished observation). Our findings are consistent with the results of a study from Lusaka, Zambia, which quantified the association between maternal viral load and infant birth outcomes, and found that greater HIV-1 disease severity, characterized as peripheral viral load above 100,000 copies per milliliter, was associated with decreased infant weight and increased infant mortality and morbidity. Several US-based studies have also quantified the association between HIV-1 disease severity and LBW (or intrauterine growth restriction). Lambert et al found that neither HIV-1 RNA copy number nor CD4 T-cell counts were associated with LBW, but increasing HIV-1 culture titer was associated with LBW; these authors also observed that timing of ART initiation—before or during pregnancy—was not associated with LBW. Tuomala et al compared women who received ART to ART-naive women and found no difference in the prevalence of LBW between the treated and untreated women. Although the authors did not report viral loads, presumably the women on ART had lower viral loads than the untreated women, and thus it can be inferred that viral load was not associated with LBW.
The relationship between severity of HIV-1 infection and PTD differed slightly from the LBW results. Among women without malaria, decreasing CD4 T-cell count, and increasing placental viral load, but not increasing peripheral viral load, was associated with increased prevalence of PTD. Unexpectedly, among women with malaria, increasing peripheral viral load was protective against PTD. Although the basis for this observed association is currently unknown, 1 study suggests that HIV-1 infection can suppress the innate immune response to P. falciparum, which has the potential to modulate inflammation and onset of delivery. Additional analyses are required to determine if this observation is biologically relevant or if it reflects an uncharacterized bias.
There are several limitations to our findings. We cannot determine if the observed associations between severity of HIV-1 infection and LBW are a direct effect of HIV-1 or if the association is secondary to HIV-associated nutritional deficiency; the sample size for the malaria-positive stratum was smaller than the sample size for the malaria-negative stratum; neither prepregnancy body mass index nor other measures of nutritional status were available for analysis; gestational ages were self-reported, and no other measures of gestational age (eg, ultrasonographic fetal measurements) were available; the results are generalizable only to ART-naive HIV-infected women, with normal blood pressure, who delivered in a hospital. Finally, cigarette smoking, a known LBW and PTD risk factor, was not assessed; however, estimates suggest that <10% of the adult population in Malawi smoke cigarettes.
Normal fetal growth represents a finely tuned immune state requiring a temporary immune tolerance to the fetal-placental unit while still enabling fetal protection from pathogens. Placental inflammation, which could result from a coinfection, can disrupt this tenuous immunological balance and cause LBW. However, clinical data from the MHP cohort suggest that coinfection with malaria or syphilis is not driving HIV-associated LBW. Furthermore, although chorioamnionitis was associated with PTD and LBW, it was not a confounder of the HIV-1 severity associations: to be a confounder, a variable must be associated with both the exposure (HIV-1 severity) and the outcome (LBW or PTD). The mean placental viral load among women with chorioamnionitis was 3.84 log10 copies per milliliter compared with 3.73 log10 copies per milliliter among women without chorioamnionitis (P = 0.5); the mean log-transformed peripheral viral load among women with chorioamnionitis was 4.43 log10 copies per milliliter compared with 4.39 log10 copies per milliliter among women without chorioamnionitis (P = 0.6), and the mean CD4 T-cell count among women with chorioamnionitis was 380 cells per microliter compared with 386 cells per microliter among women without chorioamnionitis (P = 0.9). Additional studies to determine the prevalence of other pathogenic microbes in this cohort would address the possibility that these results are confounded by a heretofore undetected coinfection.
Following the paradigm of HIV-associated disruption of the blood–brain barrier and HIV-mediated impairment of the mucosal epithelial barrier, a working hypothesis posits that HIV-1 replication impairs placental function and causes LBW. HIV-1 can replicate in the placenta and it has been detected in placental cells in vivo, and data from several groups indicate that HIV-1 can infect ex vivo placental explant cultures. Our previous work has shown that the placenta represents a unique and hospitable niche for HIV-1 replication; specifically, we observed that the concentration of HIV-1 in the placenta was different than the concentration of HIV-1 in peripheral blood. In addition to the pathogenic effects on HIV-infected cells, it is also plausible that cellular exposure to HIV-1 could be pathogenic and disrupt placental function.
In summary, indicators of severe maternal HIV-1 infection, defined as high placental or peripheral viral load or a low CD4 T-cell count, were associated in a dose-dependent manner with increased prevalence of LBW. This association was only observed in malaria-negative women, and it was not a secondary effect of PTD or in utero HIV-1 infection. The mechanism of HIV-associated LBW remains unknown.
Discussion
In this secondary analysis of a large cohort of HIV-infected pregnant women who delivered a live singleton infant in Malawi between 2000 and 2004, we tested the hypothesis that severity of HIV-1 infection is associated with risk of LBW or PTD. This cohort is unique because all women were infected with HIV-1 subtype C, were antiretroviral treatment naive, were rigorously tested for malaria, and were normotensive. This study was not designed to comprehensively determine significant predictors of LBW or PTD in HIV-infected women; rather, it was designed to characterize the independent associations between 3 specific measures of HIV-1 disease severity, LBW, and PTD, adjusting for factors that confounded or modified those associations. Although our malaria-positive sample size was small, HIV-1 severity in this group appeared not to be associated with adverse birth outcomes. However in malaria-negative women, maternal HIV-1 disease severity was significantly associated with increased prevalence of LBW and PTD. This association persisted in multivariate models adjusted for residence, primigravid status, maternal education, and maternal anemia, and the result was also robust to several sensitivity analyses, including exclusion of PTD, exclusion of infants who became HIV infected in utero, and stratification by mode of malaria diagnosis.
The average peripheral viral load of participants in this study, all of whom were antiretroviral treatment naive, was approximately 32,000 copies per milliliter. The adjusted PR for LBW corresponding to a 3-log increase in viral load among women without malaria is 2.82 (95% CI: 1.32 to 6.07), meaning that women with average viral loads have 3 times the prevalence of LBW as women with an undetectable viral load. Administration of antiretroviral therapy (ART) that reduces viral load to an undetectable limit could lead to extremely significant relative reductions in LBW among malaria-negative Malawian women.
An association between maternal HIV-1 infection and LBW has been previously observed, including several studies in Malawi. In a meta-analysis of 6 cohorts of HIV-infected Malawian women, 13% of the infants born to HIV-infected women had LBW, although malaria status was not reported. In this study, 21% of the infants born to HIV-infected women were LBW, more than double the 8% prevalence of LBW among HIV-negative women in the MHP cohort (Jess Kwiek, PhD, 2013, unpublished observation). Our findings are consistent with the results of a study from Lusaka, Zambia, which quantified the association between maternal viral load and infant birth outcomes, and found that greater HIV-1 disease severity, characterized as peripheral viral load above 100,000 copies per milliliter, was associated with decreased infant weight and increased infant mortality and morbidity. Several US-based studies have also quantified the association between HIV-1 disease severity and LBW (or intrauterine growth restriction). Lambert et al found that neither HIV-1 RNA copy number nor CD4 T-cell counts were associated with LBW, but increasing HIV-1 culture titer was associated with LBW; these authors also observed that timing of ART initiation—before or during pregnancy—was not associated with LBW. Tuomala et al compared women who received ART to ART-naive women and found no difference in the prevalence of LBW between the treated and untreated women. Although the authors did not report viral loads, presumably the women on ART had lower viral loads than the untreated women, and thus it can be inferred that viral load was not associated with LBW.
The relationship between severity of HIV-1 infection and PTD differed slightly from the LBW results. Among women without malaria, decreasing CD4 T-cell count, and increasing placental viral load, but not increasing peripheral viral load, was associated with increased prevalence of PTD. Unexpectedly, among women with malaria, increasing peripheral viral load was protective against PTD. Although the basis for this observed association is currently unknown, 1 study suggests that HIV-1 infection can suppress the innate immune response to P. falciparum, which has the potential to modulate inflammation and onset of delivery. Additional analyses are required to determine if this observation is biologically relevant or if it reflects an uncharacterized bias.
There are several limitations to our findings. We cannot determine if the observed associations between severity of HIV-1 infection and LBW are a direct effect of HIV-1 or if the association is secondary to HIV-associated nutritional deficiency; the sample size for the malaria-positive stratum was smaller than the sample size for the malaria-negative stratum; neither prepregnancy body mass index nor other measures of nutritional status were available for analysis; gestational ages were self-reported, and no other measures of gestational age (eg, ultrasonographic fetal measurements) were available; the results are generalizable only to ART-naive HIV-infected women, with normal blood pressure, who delivered in a hospital. Finally, cigarette smoking, a known LBW and PTD risk factor, was not assessed; however, estimates suggest that <10% of the adult population in Malawi smoke cigarettes.
Normal fetal growth represents a finely tuned immune state requiring a temporary immune tolerance to the fetal-placental unit while still enabling fetal protection from pathogens. Placental inflammation, which could result from a coinfection, can disrupt this tenuous immunological balance and cause LBW. However, clinical data from the MHP cohort suggest that coinfection with malaria or syphilis is not driving HIV-associated LBW. Furthermore, although chorioamnionitis was associated with PTD and LBW, it was not a confounder of the HIV-1 severity associations: to be a confounder, a variable must be associated with both the exposure (HIV-1 severity) and the outcome (LBW or PTD). The mean placental viral load among women with chorioamnionitis was 3.84 log10 copies per milliliter compared with 3.73 log10 copies per milliliter among women without chorioamnionitis (P = 0.5); the mean log-transformed peripheral viral load among women with chorioamnionitis was 4.43 log10 copies per milliliter compared with 4.39 log10 copies per milliliter among women without chorioamnionitis (P = 0.6), and the mean CD4 T-cell count among women with chorioamnionitis was 380 cells per microliter compared with 386 cells per microliter among women without chorioamnionitis (P = 0.9). Additional studies to determine the prevalence of other pathogenic microbes in this cohort would address the possibility that these results are confounded by a heretofore undetected coinfection.
Following the paradigm of HIV-associated disruption of the blood–brain barrier and HIV-mediated impairment of the mucosal epithelial barrier, a working hypothesis posits that HIV-1 replication impairs placental function and causes LBW. HIV-1 can replicate in the placenta and it has been detected in placental cells in vivo, and data from several groups indicate that HIV-1 can infect ex vivo placental explant cultures. Our previous work has shown that the placenta represents a unique and hospitable niche for HIV-1 replication; specifically, we observed that the concentration of HIV-1 in the placenta was different than the concentration of HIV-1 in peripheral blood. In addition to the pathogenic effects on HIV-infected cells, it is also plausible that cellular exposure to HIV-1 could be pathogenic and disrupt placental function.
In summary, indicators of severe maternal HIV-1 infection, defined as high placental or peripheral viral load or a low CD4 T-cell count, were associated in a dose-dependent manner with increased prevalence of LBW. This association was only observed in malaria-negative women, and it was not a secondary effect of PTD or in utero HIV-1 infection. The mechanism of HIV-associated LBW remains unknown.
