LBW and PTD Are Common in Malawi
In this cohort of HIV-infected women, 21% of participants delivered a LBW infant and 16% delivered preterm. Age, malaria status, and gravidity were not associated with prevalence of LBW or PTD (Table 2). Anemia was more common among women with infants with LBW (68%) and PTD (68%) compared with women with normal weight term infants (52%). Chorioamnionitis was also more commonly observed in the LBW (33%) and PTD (37%) groups compared with the normal weight term delivery group (23%). Female sex was more prevalent among LBW infants (57%) compared with normal weight term infants (46%). Finally, syphilis seropositivity was more common among mothers of PTD infants (11%) than normal weight term infants (6%) (Table 2).
Placental Viral Load Correlates With Birthweight and Gestational Age
Maternal peripheral HIV-1 viral load was inversely correlated with continuous infant birthweight (correlation coefficient = −0.08, P = 0.06), but not with continuous duration of gestation (correlation coefficient = −0.05, P = 0.5) (Figs. 1A, C). HIV-1 concentration in the placenta was inversely correlated with both birthweight (correlation coefficient = −0.15, P = 0.01) and duration of gestation (correlation coefficient = −0.20, P = 0.0008) (Figs. 1B, D).
The effect of HIV-1 disease severity on prevalence of LBW differed meaningfully by maternal malaria status. Residence, education level, primigravid status, and anemia were retained as confounders in adjusted multivariable models. Among women with malaria, we observed no significant association between any measure of HIV-1 disease severity and prevalence of LBW in unadjusted or adjusted analyses (Table 3). Among malaria-negative women, for all measures of HIV-1 disease severity, more severe HIV-1 disease was significantly associated with increased prevalence of LBW in both unadjusted and adjusted models. The adjusted PR for a 1-log increase in placental HIV-1 viral load was 1.22 (95% CI: 1.00 to 1.48); for a 1-log increase in peripheral HIV-1, viral load was 1.38 (95% CI: 1.08 to 1.77); and for a 100-cell per microliter decrease in CD4+ T cells was 1.12 (95% CI: 1.05 to 1.21) (Table 3).
The effect of HIV-1 disease severity on prevalence of PTD also differed by maternal malaria status (Table 4). Among malaria-positive women, neither placental viral load nor CD4+ T-cell count were significantly associated with PTD in unadjusted or adjusted analyses, but a 1-log increase in peripheral viral load was significantly protective against PTD in adjusted analyses (PR: 0.56, 95% CI: 0.47 to 0.85). Among women without malaria, higher placental viral load and lower CD4+ T-cell count were both significantly associated with increased prevalence of PTD (adjusted PR for a 1-log increase in placental viral load: 1.29, 95% CI: 1.02 to 1.63; adjusted PR for 100-cell per microliter decrease in CD4+ T cells: 1.16, 95% CI: 1.05 to 1.28). Increases in peripheral HIV-1 viral load did not significantly increase prevalence of PTD in malaria-negative women (Table 4).
The Association Between HIV-1 and LBW Remains After Exclusion of PTD and HIV-Infected Infants
When the data set was restricted to include only infants born after 37 weeks' gestation (n = 662), the associations between HIV-1 severity and prevalence of LBW among women with malaria were strengthened, but remained not statistically significant: the adjusted PR for a 1-log10 increase in placental viral load was 1.64 (95% CI: 0.98 to 2.74) compared with 1.26 (95% CI: 0.87 to 1.83) in the primary analysis (see Table S1, Supplemental Digital Content,http://links.lww.com/QAI/A445). The PR for LBW for a 1-log10 increase in peripheral HIV-1 viral load was 1.66 (95% CI: 0.80 to 3.47) compared with 0.88 (95% CI: 0.57 to 1.35) in the primary analysis. However, excluding these observations had almost no affect on the magnitude of the associations between HIV-1 severity and prevalence of LBW in women without malaria. Given the reduced sample size, many of the PRs are no longer statistically significant, but the strength of the associations was essentially unchanged (see Table S1, Supplemental Digital Content,http://links.lww.com/QAI/A445).
When the data set was restricted only to observations with infants known to be HIV negative at birth (n = 686), we observed no meaningful changes in the associations between HIV-1 severity and prevalence of LBW or PTD for malaria-positive or malaria-negative women (see Table S2 and S3, Supplemental Digital Content,http://links.lww.com/QAI/A445). Thus, the observed associations in our primary analysis between HIV-1 severity and LBW or PTD are unlikely to be explained by infant HIV-1 status at birth.
Our primary analysis established that most associations between HIV-1 severity and birth outcomes were meaningfully different by malaria status. Our final sensitivity analysis assessed whether our findings were robust to the method of malaria diagnosis; in other words, was the same pattern observed for women with malaria diagnosed by peripheral blood smear, placental blood smear, and placental histology? For both LBW and PTD, the patterns observed in the primary analysis were repeated in the sensitivity analysis, with no meaningful differences by method of malaria diagnosis (see Table S4 and S5, Supplemental Digital Content,http://links.lww.com/QAI/A445).
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,1,2 including several studies in Malawi.3,18 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.3 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.25 Several US-based studies have also quantified the association between HIV-1 disease severity and LBW (or intrauterine growth restriction). Lambert et al26 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 al27 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,28 which has the potential to modulate inflammation and onset of delivery.29,30 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 measurements31) 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.32
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 barrier33 and HIV-mediated impairment of the mucosal epithelial barrier,34 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,35 and data from several groups indicate that HIV-1 can infect ex vivo placental explant cultures.36,37 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.13 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.
The authors are grateful for the participation of the Malawian women and their newborns and the Malaria and HIV-1 in Pregnancy Cohort Staff.
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HIV-1; adverse birth outcomes; low birth weight; preterm delivery; placenta; Malawi
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