Positive effect of large birth intervals on early childhood hemoglobin levels in Africa is limited to girls. Cross-sectional DHS study
Robel Afeworki,1 Jeroen Smits,2 Jules Tolboom,3 Andre van der Ven1
1Nijmegen Institute for International Health, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
2Nijmegen Center for Economics, Institute for Management and Research, Radboud University Nijmegen, Nijmegen, The Netherlands.
3Department of Paediatrics, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Short birth intervals are independently associated with increased risk of adverse maternal, perinatal, infant and child outcomes. Anemia in children, which is highly prevalent in Africa, is associated with an increased risk of morbidity and mortality. Birth spacing is advocated as a tool to reduce anemia in pre-school African children, but the role of gender differences and contextual factors has been neglected. The present study aims to determine to what extent the length of preceding birth interval influences the hemoglobin levels of African pre-school children in general, as well as for boys and girls separately and which contextual factors thereby play a crucial role.
Methods and Findings
This cross-sectional study uses data from Demographic and Health Surveys (DHS) conducted between 2003 and 2011 in 20 African countries. All pre-school children aged 6-59 months with a valid hemoglobin measurement and a preceding birth interval of 7-72 months as well as their corresponding multigravida mothers aged 21-49 years were included in the study. Hemoglobin levels of children and mothers were measured in g/l, while birth intervals were calculated as month’s difference between consecutive births. Multivariate analyses were done to examine the relationship between length of preceding birth interval and child hemoglobin levels, adjusted for factors at the individual, household, community, district, and country level. A positive linear relationship was observed between birth interval and the 49,260 included children’s hemoglobin level, whereby age and sex of the child, hemoglobin level of the mother, household wealth, mother’s education and urbanization of place of residence also showed positive associations. In the interaction models, the effect of a month increase in birth interval is associated with an average increase of 0.025 g/l in hemoglobin level (P=0.001) in girls ,while for boys the effect was not significant. In addition, for girls, the effect of length of preceding birth interval was highest in young mothers and mothers with higher hemoglobin levels while for boys, the highest effect was noticed for those living in more highly educated regions. Finally, significantly higher hemoglobin levels of girls compared to boys were observed at birth but with increasing age, the sex difference in hemoglobin level gradually becomes smaller.
A longer birth interval has a modest positive effect on early childhood hemoglobin levels of girls, and this effect is strongest when their mothers are in their early twenties and have a high hemoglobin level. Remarkably, although the physiological iron requirement is higher for boys than girls, birth spacing has little influence on hemoglobin levels of preschool boys. We speculate that the preference for male offspring in large parts of Africa significantly influences nutritional patterns of African preschool boys and girls and as such also determines the different effect of birth spacing. Finally, gender aspects should be considered in intervention programs that aim to improve anemia in Africa children.
Anemia is a main public health concern in low income countries where children and women are the most affected members of the community. The global health reports from WHO indicates that highest burden of anemia are observed in 68% of preschool children and 57% of pregnant women from Sub-Saharan countries .The etiology of childhood anemia in Africa is multifactorial, including nutritional iron and folate deficiencies [2,3], and parasitic diseases like malaria, hookworm and schistosomiasis [4,5] are its principal causes. In the past decades, an integrated package of intervention using food fortification, family planning and birth spacing has been the mainstream strategy of addressing multiple causes of anemia in the scope of public health . It is well established the length of birth spacing tends to influence different health outcome measures for mother, newborn and child. Similarly, maternal depletion syndrome (MDP), that is characterized by a negative change in maternal nutritional status during the reproductive cycle and which is influenced by the length of birth interval, also impairs the health outcome of children [7,8]. One may hypothesize that increasing the birth interval may result in less anemia as well, as the mother’s body will have more time to fully recover from giving birth and replenish stores of nutrients, including iron that may have been exhausted during pregnancy, delivery and lactation. Various birth spacing studies has documented short birth intervals less than 2 years and long birth intervals more than 5 years leads to adverse pregnancy and child outcomes [9-11]. However, the optimal duration of birth interval is still unclear and large-scale studies exploring the relation between birth spacing and anemia in pre-school children are still lacking, despite the circumstantial evidences are suggesting a positive relation.
The aim of the present study is therefore to determine to what extent the length of preceding birth interval influences the hemoglobin levels of African pre-school children in general, as well as for boys and girls separately and which contextual factors thereby play a crucial role.
The study used cross-sectional data derived from the Demographic and Health Surveys (DHS) conducted between 2003 and 2011 in 20 African countries. DHS are large, nationally representative household surveys, held in many low-income countries since the 1980’s, measuring indicators of population, health, and nutrition, with special emphasis on maternal and child health. A total of 49,260 pre-school children aged 6-59 months with their corresponding multigravida mothers aged 21-49 years, valid hemoglobin measurement and a preceding birth interval of 7-72 months were included in the study. Hemoglobin levels of children and mothers were measured in g/l, while preceding birth interval, the period between the previous childbirth and the index child birth, was expressed in months (Figure 1). The difference in months between two consecutive live births was considered as a birth interval.
A statistical models were built to examine the relationship between length of preceding birth interval and child hemoglobin levels, adjusted for factors at the individual, household, community, district, and country level. In addition statistical analysis for separate sex groups with interaction terms were performed to examine the influence of characteristics of the children, their mothers, the households and the context on the strength of the preceding birth interval effect. For the sake of clarity the factors used are categorized into four groups: Characteristics of the children (age, sex, birth order and twin status), characteristics of the mother (age, hemoglobin level, body mass index, currently breastfeeding, status within the household (age difference with the partner), number of unions, employment status), contextual factors (mean years of education of adults, preventive health measures (proportion of children having received vaccination against measles), cluster altitude, level of development (percentage of households owning a television) and the availability of health facilities (proportion of last births delivered in a clinic/hospital)).
Our data yield several important findings with regard to the birth interval effect. First, we found that the length of the preceding birth interval has a modest positive effect on hemoglobin levels of African preschool girls, but not of that of boys. Second, having a long preceding birth interval is particularly important for African girls with a young mother. Third, girls were also found to profit more if their mother has a higher hemoglobin level. Fourth, boys were found to profit from a longer birth interval only under specific circumstances, namely if they lived in an area where the educational level of mothers is high.
The present study is unique in using hemoglobin as outcome parameter and studying its effects in gender differences. Using hemoglobin level as outcome is important, because it is sensitive indicator of well being or general health status. As anemia is highly prevalent in African mothers and children, this indicates an urgent need for effective interventions [1,2,9]. Our findings demonstrated the focus on gender differences turned out to have an important aspect in bolstering public health strategies. When studying differences between boys and girls, while controlling for confounding factors, a significant effect of longer birth interval was particularly found for girls but turned out to be insignificant for boys. The positive effect observed in girls was in the order of 0.025 g/l for a one month increase in the birth interval, or 0.3 g/l for an increase of a year. In addition, we found that the highest hemoglobin increments were noticed in girls with young mothers and in girls with mothers with a high hemoglobin levels (Figure 2). Compared to girls with the oldest mothers in our data (late forties) and the mothers with the lowest hemoglobin levels (under 60), for those with the youngest mothers (early twenties) and with the mothers with the highest hemoglobin levels (over 160) the effect of a year increase in birth interval is associated with an approximate increase of 1.4 g/l in hemoglobin level. Given that the effects are additive, for girls with a young mother with a high hemoglobin level the birth interval effect is in the order of 2.8 g/l higher than for those with an old mother with a low hemoglobin level. Childhood anemia is very prevalent in Sub-Sahara Africa but gender differences are thereby rarely considered. Our results suggest that increasing hemoglobin levels in mothers may positively affect hemoglobin levels in their daughters. Furthermore, it seems important to target the interventions especially to young mothers, as their female offspring profits most from longer birth intervals.
In contrary, we did not find a significant overall effect of birth interval on hemoglobin level among boys. However, the interaction analysis made clear that in areas where mothers have relatively high educational levels, boys profit more from a longer birth interval than in areas where mothers have relatively low educational levels (Figure 2). This difference is in the order of 1 g/l for an increase of a year.
We hypothesize the different sex response observed to birth spacing can be explained based on the preference for male offspring in many African countries which possibly leads to more maternal investments in boys compared to girls, making them less susceptible for the effect of birth spacing. Studies from Ethiopia (Quisumbing,2003)  and Peru (Gerlter and Gleewe,1992)  indeed showed that larger investments in boys are made, while findings from India show that girls are disadvantaged with less investment in health inputs and outcomes .The difference in investments for boys compared to girls may be expressed through several socioeconomic and contextual factors. Studies from Africa show that birth spacing is shorter after the delivery of a girl than of a boy [15,16] and in young compared to older mothers [16,17]. The first factor may also have to do with sex preference and investment in boys while the age effect of mothers may relate difference in fecundity rate and timing of family building responsibilities .
The maternal depletion syndrome could be another factor that contributes to hemoglobin levels of their offspring. Maternal depletion syndrome is characterized by a deterioration of the maternal nutritional status during the reproductive cycle, especially when the period of depletion is long while the time for repletion is short and the mother has a marginally inadequate food intake [8,18]. For instance, inadequate iron and folic acid intake during the reproductive period affect the maternal status for these nutrients during the interpregnancy interval and iron and folic acid deficiency has been associated with preterm births and fetal growth retardation.. Lower fecundity or longer birth intervals may provide mothers with an opportunity window to replenish iron loss from a previous pregnancy and delivery and sustain physiological recuperation for the following one. Similarly, the offspring’s hemoglobin level may gain from a longer preceding birth interval as it depends on maternal iron status, beside other factors such as gestational age, birth weight and timing of umbilical cord clamping .
Given that no significant association between preceding birth interval and the children’s age was found, our study also indicates that the positive effects of a longer birth interval persist across the first 6 years of life. This may be explained by the fact that the age difference between the two succeeding children remains, which may create the opportunities for more maternal investments over the whole period. In addition, also biological factors, like epigenetic changes may contribute to the constant positive effect of a longer birth interval. The clinical relevance of our finding is difficult to give, as the effects on hemoglobin levels are only modest and mostly seen in girls that have already a greater chance of survival while boys are biologically weaker and more susceptible to disease and premature death [21,22].
Apart from the birth interval effect, our analyses made clear that hemoglobin levels of African children steadily increase during the first 59 months of life and that hemoglobin levels of girls were significantly higher than those of boys. An additional test for sex differences in the age effect revealed a significant interaction, whereby the increment with age is significantly stronger in boys than in girls. Hence, with increasing age, the sex difference in hemoglobin level becomes smaller (Figure 3).
In conclusion, increasing birth interval has a moderate positive effect on hemoglobin levels of preschool African girls. Remarkably, although iron requirement of boys seem higher than girls, birth spacing did not influence hemoglobin levels of preschool boys. The preference for male offspring in large parts of Africa may not only significantly contribute to the sex differences in hemoglobin levels but may also determine the different effect of birth spacing on hemoglobin levels of African boys and girls. Finally, gender aspects should be considered in interventions programs that aim to improve anemia in African children.
The content of the work presented here is solely the responsibility of the authors and does not necessarily represent the official views of any health organizations. The authors are grateful for the resources of DHS. Without the DHS data, this work would not have been possible; we thank the respondents, field staff and management of the site for sharing their indispensible data and allowing us to use it indefinitely.
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