Baseline characteristics of mothers and infants included in this analysis are presented in Table 1. Many maternal characteristics, including age, number of pregnancies, marital status, education level, and hemoglobin level at the time of enrollment, did not differ significantly between groups. Mothers taking HAART during pregnancy had more personal income, even after adjustment for inflation, compared with women who took ZDV during pregnancy and were more likely to have electricity at home. Over 50% of the women in each exposure group reported the current pregnancy to be either their first or second pregnancy.
The maternal enrollment CD4+ counts for women in the ZDV exposure group were higher compared with the HAART group (median 392 cells/mm3 versus 331 cells/mm3, P < 0.001); 24% of infants exposed to HAART in utero were born to mothers with enrollment CD4+ counts less than 200 cells/mm3, whereas only 11% of infants exposed to ZDV in utero were born to mothers with enrollment CD4+ counts less than 200 cells/mm3. Therefore, a stratified analysis of CD4+ cell count was undertaken based on maternal enrollment CD4+ cell count either less than 200 cells/mm3 or 200 cells/mm3 or greater (Table 2). Baseline plasma HIV-1 RNA viral load was higher for women in the ZDV exposure group compared with women in the HAART exposure group (median 4.34 log10 copies/mL versus 4.18 log10 copies/mL, P = 0.02).
There were no statistically significant differences in gender or distribution of gestational age of infants between the two groups nor was there a difference in the percent of infants born small for gestational age, defined as a weight of less than 2500 g for an infant at 37 weeks or greater gestational age. Median duration of in utero exposure to HAART (12.1 weeks; range, 2.6-22.3 weeks) was longer than median duration in utero exposure to ZDV (5.7 weeks; range, 2.0-10.9 weeks) as a result of study design differences relative to gestational age at enrollment between the Mma Bana and Mashi studies.
Weight and Length at Birth
Infants exposed in utero to HAART had a mean birth weight z-score of -0.64, whereas the ZDV-exposed group had a birth weight z-score of -0.34 (P < 0.001) (Table 2). These differences were similar for both male and female subgroups, but mean birth weight z-scores were lower for females. In a stratified analysis of normalized weight for age based on maternal enrollment. CD4+ cell count of either less than 200 cells/mm3 or 200 cells/mm3 or greater; mean birth weight z-score was lower if maternal CD4+ cell count was less than 200 cells/mm3 compared with 200 cells/mm3 or greater regardless of exposure group (Table 2).
Overall, the birth length z-score was also higher in the ZDV-exposed group. However, in stratified analysis based on maternal enrollment CD4+ count, this difference was only statistically significant for infants born to mothers with CD4+ counts 200 cells/mm3 or greater in which the ZDV group had a mean birth length z-score of 0.08 versus a mean birth length z-score of -0.15 (P = 0.018). This same trend was observed in birth WLZ.
Growth Over 6 Months
Weight for Age
Controlling for enrollment site, maternal enrollment CD4+ as a binary variable (less than 200 cells/mm3 or 200 cells/mm3 or greater), maternal body mass index at 1 month postpartum, and infant gender, using a liner mixed-effects model, infants exposed to HAART in utero had a lower birth weight z-score but a more rapid increase in WAZ during the first 2 months of life than the ZDV-exposed infant group (P = 0.03). From 3 months through 6 months of life, the two groups experienced similar rates of weight gain for age (P = 0.26) (Fig. 3).
Length for Age
In adjusted analyses, the mean change in age-adjusted LAZ differed significantly between the two exposure groups from birth through the 2 months of life (P = 0.002) (Fig. 3). From the third through sixth months of life, the mean change in the LAZ for both the HAART- and ZDV-exposed infants was no longer statistically different (P = 0.08). When comparing absolute differences in mean recumbent length at 6 months of life between exposure groups by gender, mean recumbent length for HAART-exposed males was 0.4 cm shorter than ZDV-exposed males. The difference in mean recumbent length for females by exposure group at 6 months of life was 1.0 cm with HAART-exposed female infants on average having a lower recumbent length.
Weight for Length
In adjusted analyses using a linear mixed-effects model, the HAART-exposed group had a more rapid increase in WLZ during the first 2 months of life compared with the ZDV-exposed group (P < 0.0001) such that the mean for this group was higher than the mean score of the ZDV-exposed group at 2 months of life (Fig. 3). From the third through the sixth months of life, the mean WLZ z-score in the HAART-exposed group declined, reflecting a more rapid increase in LAZ than WAZ. Over the same period, the ZDV-exposed group had a modest increase in mean WLZ z-score. These distinctively different growth patterns by exposure group from the third through the sixth month of life were statistically different (P = 0.04).
Wasting and Stunting
There was no significant difference in the proportion of infants between exposure groups meeting criteria for wasting (2 or less standard deviations below norm for WLZ z-score) or stunting (2 or less standard deviations below norm for LAZ z-score) at 6 months of life. Wasting was present in 6.02% of the ZDV-exposed infants and 6.09% of the HAART-exposed infants (P = 0.96) at 6 months of life. Stunting was present in 4.76% of the ZDV-exposed group and 4.70% of the HAART-exposed infants (P = 0.96) at 6 months of life.
This is the first study to compare early growth of infants over time after in utero HAART or ZDV exposure. At birth, infants exposed to HAART in utero had significantly lower weight, length, and weight-for-length normalized scores compared with those exposed to ZDV in utero. However, weight differences were not apparent by 3 months of age and the incidence of wasting (defined as WLZ falling more than 2 standard deviations below norm) did not differ significantly between the two groups at 6 months of life.
It is reassuring that mean infant weights in the HAART-exposed group improved rapidly over the first 3 months of life with the two exposure groups experiencing an overlapping mean normalized weight pattern from 3 months through 6 months of life. In an exploratory analysis, the normalized longitudinal growth pattern was similar for infants in the HAART exposure group regardless of the maternal regimen. However, the lower mean birth weight for HAART-exposed HIV-uninfected infants represents a potential for higher rates of early infant mortality and/or morbidity. Survival rates for low-birth-weight infants remains a challenge in many resource-limited settings, including those where HAART is now becoming increasingly available for maternal treatment and for PMTCT. In the Mashi study as well as a cohort from the Zambia Exclusive Breastfeeding Study, low birth weight was associated with increased infant mortality.22,23 A study from Tanzania that evaluated risk factors for infant mortality among HIV-exposed infants observed that lower birth weight, but not transmission of HIV, was associated with higher mortality in the first 28 days of life; for infants who remained HIV-negative, lower birth weight continued to be associated with a higher risk of mortality after the first month of life and through the first year of life.24 Therefore, infants exposed to maternal HAART may benefit from programs to optimize growth in the first several months of life in an effort to mitigate morbidity and mortality.
Although HAART-exposed infants were observed to have shorter normalized LAZ throughout the first 6 months of life, their mean normalized WLZ was more age-appropriate by the second month of life than the ZDV-exposed cohort and there was no statistically significant difference between exposure groups in the proportion of infants with growth stunting according to WHO guidelines. Of note, we were unable to identify a biologically plausible explanation for shorter mean LAZ among HAART-exposed infants, and this presents an opportunity for further research. The clinical significance of lower normalized LAZ for HAART-exposed infants at 6 months of life is uncertain and should be interpreted with caution. However, as Mma Bana infants continue to be followed beyond 6 months of life, the pattern in normalized mean length can be re-evaluated and correlated with morbidity and/or mortality outcomes.
Maternal HAART provided a possible advantage to infants in terms of normalized WLZ in comparison to infants exposed to in utero ZDV and ongoing ZDV prophylaxis during breastfeeding. Overall, the cohort of infants exposed to HAART in utero were observed to have normalized WLZ that approached or exceeded norms from 2 months of life through 6 months of life, whereas the ZDV exposure group had lower normalized WLZ over this same period. In resource-limited settings where infants are at higher risk of infant morbidity and mortality from diarrheal disease and respiratory illnesses, infants with WLZ that are near normal may have a survival advantage. This hypothesis is consistent with reports of lower mortality among infants whose mothers received HAART in Malawi.25 However, further studies are required to confirm whether better WLZ correlates with infant survival and whether it mediates any observed benefit from maternal HAART.
Findings of this study should be considered in the context of protocol differences, which represent the major limitation of this study. First, Mashi ZDV-exposed infants received prophylactic ZDV throughout the period of breastfeeding up to 6 months of life, whereas Mma Bana infants only received 4 weeks of ZDV. Although the reported differences at birth by exposure group were not impacted by this issue, if ZDV prophylaxis during breastfeeding affected infant growth, it would represent a confounder with respect to longitudinal results. Second, mean duration of in utero ARV exposure differed significantly between the groups as a result of each study's enrollment protocol, and the potential impact of different exposure durations could not be evaluated. However, no differences were observed when we included or excluded HAART-exposed infants from the Mashi cohort, and we found no trend for lower z-scores among infants with longer HAART exposure in the Mma Bana cohort (data not shown). Third, it is possible that if lower-weight infants died during the period of the study at a higher rate than larger infants, then observed mean weight gain within either group could be a function of informative censoring by death. However, only 13 (2.1%) infants in the HAART exposure group and 12 (2.7%) infants in the ZDV exposure group died during the first 6 months of life. Therefore, this small number of deaths would be unlikely to influence the overall findings.
Finally, although the Mashi and Mma Bana studies were conducted at the same four sites in Botswana, the Mashi study took place before the Mma Bana study and temporal differences (including limited HAART availability and lower inflation-adjusted income in the Mashi study period) may have influenced study findings. Of note, there were no policy changes calling for nutritional, vitamin, or mineral supplementation between these studies and the fact that both cohorts of infants were exclusively breast-fed controlled for differences in the infants' nutritional status. We controlled for baseline CD4+ cell count differences in the linear mixed-effects model and by stratifying infant growth outcomes by maternal enrollment CD4+ cell counts as a binary variable, either less than 200 cells/mm3 or 200 cells/mm3 or greater (Table 2). Although maternal plasma HIV-1 RNA level also differed by exposure groups, it was neither a significant predictor nor an effect modifier of growth outcomes.
In summary, HIV-uninfected infants exposed in utero to HAART had lower birth weight than comparable infants exposed to short-course ZDV, but subsequent weight gain was rapid and approached the norm for age and gender by 3 months of life. HAART exposure was associated with lower mean infant length throughout the first 6 months of life. Although statistically significant, the lower mean length coupled with weight gain resulted in more age- and gender-appropriate normalized WLZ for HAART-exposed infants. Higher WAZ have been noted to have a survival benefit.21 This analysis is the first to provide reassurance that lower birth weight associated with in utero HAART exposure does not persist during early infancy. It also highlights the importance of early and routinely scheduled health care for HAART-exposed HIV-uninfected infants.
We are indebted to the women and infants who participated in the Mashi and Mma Bana studies, Mashi and Mma Bana study teams as well as the administration and staff at Scottish Livingstone, Deborah Retief Memorial, Athlone and Princess Marina Hospitals, and the staff at the referring health clinics.
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Keywords:© 2011 Lippincott Williams & Wilkins, Inc.
prevention of mother-to-child transmission; HIV; growth