In this study of infants born to HIV-infected mothers in Botswana, exposure to maternal HAART was associated with a significantly higher risk of severe anemia during the first 6 months of life compared with exposure to maternal zidovudine alone. Among breastfeeding infants, assignment to in utero and breast milk HAART exposure (HAART-BF) was associated with an estimated 2.6-fold increased odds of severe anemia compared with infants assigned to in utero and 6 months of postnatal zidovudine exposure (ZDV-BF). Formula-fed infants assigned to in utero and 1 month of zidovudine (ZDV-FF) experienced the lowest risk of anemia, 5.8-fold and 2.2-fold decreased odds compared with HAART-BF and ZDV-BF, respectively.
The results of this study are in agreement with the findings of observational studies of largely formula-feeding cohorts in the United States and Europe that have demonstrated lower hemoglobin concentrations among infants exposed to in utero
HAART compared with infants exposed to monotherapy or no in utero
Calculating from the incidence of anemia reported for a cohort of 215 German infants born in a German,41
HAART-exposed infants had 3.9-fold increased odds of severe anemia compared with infants exposed to mono- or dual-antiretroviral therapy, similar to the findings in our study. Our study, utilizing a controlled design, confirms findings reported in observational studies and extends the findings to African and breastfeeding populations.
An earlier analysis by Bae et al.42
comparing toxicity in a subset of Mashi study infants exposed and unexposed to maternal HAART did not identify a signal for increased risk of severe anemia with HAART exposure, and recommended larger studies. The apparent contradiction with our present findings can be understood by considering differences in sample size, inclusion criteria, and toxicity definitions. The Bae et al.
analysis included only 178 infants (compared with 1719 infants in the present analysis), and had consequently had reduced power to detect differences. The earlier (but not the current) analysis included HIV-infected infants, who are at increased risk for severe anemia.34
Maternal HAART potently prevented HIV-infection in Mashi, potentially biasing results towards null of no effect of maternal HAART on severe infant anemia. Most importantly, the Bae et al.
analysis used the prior 1994 version of the DAIDS toxicity table43, 44
which did not incorporate the expected hemoglobin recovery from the physiologic nadir of infancy. Re-grading the 178 infants in the Bae et al.
cohort using the 2004 DAIDS toxicity table33
and excluding HIV-infected infants, exposes a pattern similar to the present analysis— 11.9% of HAART-exposed infants and 5.9% of ZDV-monotherapy-exposed infants developed severe anemia through 7 months of age (P=0.185).
The mechanism for the observed increase in severe anemia due to maternal HAART exposure is uncertain. Infants in the HAART-BF and ZDV-BF groups appeared to experience a deeper and more prolonged physiologic nadir in hemoglobin. Infants in the HAART-BF group were exposed to in utero
zidovudine for a median of 11.5 weeks compared to 5.6 weeks in the ZDV-FF and ZDV-BF groups, but direct infant ZDV receipt occurred for a longer period in the ZDV-BF group. If zidovudine were the principal cause of severe anemia, we would have expected the greatest incidence of severe anemia in the ZDV-BF group exposed to 6 months of postnatal zidovudine, particularly given minimal exposure to zidovudine via breast milk in the HAART-BF group.45
The fact that the HAART-BF group had more severe anemias suggests that either the timing of exposure or the combination of ZDV with other antiretrovirals may be important considerations. In a randomized trial in Malawi of postnatal maternal HAART, rates of severe anemia were similar between infants with exposure to HAART via breast milk and those without exposure to antiretrovirals in breast milk,15
suggesting that it is in utero
exposure that increases risk for anemia. The addition of lamivudine may also promote the hematologic toxicity of ZDV as suggested by several case reports46-48
and one controlled trial49
in adults. However, other larger controlled trials have not reported this effect.50, 51
The type of infant anemias that we observed is noteworthy. Despite universal exposure to zidovudine, which promotes macrocytosis, microcytic (and hypochromic) anemia were common, particularly among HAART-exposed infants, suggesting a role of iron-deficiency. Mothers in both the Mashi and Mma Bana studies were provided iron supplementation as part of antenatal care. It is possible that HAART-exposure could increase vulnerability of hematopoiesis to nutrient deficiencies, infection, or other insults. Additionally, HAART could impair the transfer of iron from mother to fetus as suggested by decreased total hemoglobin iron estimated in HAART-BF infants. The observed morphology of infant red blood cells and the decreased hemoglobin iron suggest that infant iron supplementation should be considered.
This study is subject to several limitations. The assigned exposures of the Mashi and Mma Bana trials preclude separation of antiretroviral and feeding effects, since almost all HAART-exposed infants were breastfed. A comparator group of HIV-exposed infants without exposure to antiretroviral treatment would be informative but unethical. Our analysis cannot separate contributions of antenatal and post-natal antiretroviral exposure towards anemia. Another potential limitation of our analysis was the difference in study timing— HAART-BF infants were from the Mma Bana study whereas the ZDV-BF and ZDV-FF groups were from the earlier Mashi study. However, mothers assigned to HAART were more likely to have higher incomes, more education, and live in urban areas, reflecting the economic development in the years between Mashi and Mma Bana. Consequently, the effect of measured or unmeasured socioeconomic and nutritional factors would be expected to be favorable to HAART-BF infants, decreasing their incidence of severe anemia. Additionally, measured differences in maternal or infant characteristics between comparator groups were controlled for in multivariate analyses, and indeed some of these factors (such as small for gestational age and prematurity) may be associated with in utero
For these reasons, our findings may underestimate the impact of maternal HAART on the incidence of severe early infant anemia. Nevertheless, our study design cannot conclusively establish causality between in utero
HAART exposure and infant anemia, and further study of this important question is warranted.
The clinical implications of our findings also require further study. The majority of infants with severe anemia in the Mashi and Mma Bana trials did not have symptoms reported. Observational studies in Africa suggest that severe anemia is associated with increased mortality, however these studies have typically used a much lower hemoglobin threshold (<5.0 mg/dL) to define severe anemia28
than was used in this study. Our analysis used the DAIDS toxicity table definitions for severe anemia— less than 10 mg/dL at birth, 8 mg/dL at 1 month, and 9 mg/dL at 3 and 6 months.33
Data to describe the impact of less severe anemia are scant. In Tanzania, using a similar hemoglobin threshold of < 8.5 mg/dL, HIV-exposed infants with iron-deficiency anemia were approximately twice as likely to die prior to 2 years of age.55
Anemia may have contributed to 6 infant deaths in our study, but only one of these infants was HAART-exposed in utero
. It is possible that routine screening and access to transfusion prevented additional deaths, particularly among the HAART-exposed infants.
While our analysis focused on severe anemia, HAART-BF infants also had lower hemoglobin measurements at 3 and 6 months and were more likely to have any grade of anemia. Mild or moderate anemia due to iron deficiency is of significant public health importance due to its association with impaired child development.56
It remains uncertain whether anemia in the absence of iron deficiency impairs child development,57
however the possibility of an adverse effect of maternal HAART, mediated via anemia, on subsequent infant development should be explored.
In summary, we have shown that maternal HAART started in pregnancy and continued during breastfeeding was associated with increased severe infant anemia. Confirmation of this finding and the etiology of anemia in HAART-exposed infants deserve further study. Given the established benefits of HAART for the prevention of MTCT11-14, 58
and promotion of maternal health,59
the clinical implications of laboratory-detected toxicity should be considered carefully. Mitigating strategies such as iron-supplementation to HIV-exposed breastfed infants or alternative antiretrovirals should be evaluated to maximize the benefits of maternal HAART while minimizing potential risks.