hildren born in the richest 20% households. Households that lacks of a hygienic toilet facility were associated with higher risk of infant mortality. Similarly, non-availability of safe drinking water in households was associated with higher risk of infant mortality. Infant mortality rate was higher in rural area than in urban area; and it was considerable higher in North East than other geographical divisions.
For children born in the five years preceding the NDHS, the survival probabilities for children born singleton and multiple-birth by single months of age before 12 months was presented in Figure 1. The figure shows that the two survival curves diverge beyond the second month of age, with children born multiple-birth having progressively lower survival probability than children born singleton. The difference in survival probability between children born singleton and multiple-birth was non-random as judge by log-rank test of survival functions (chi-squared = 16.01 on one degree of freedom; p = .001). The large majority of multiple birth children died in infancy.
The unadjusted hazard ratio for the effect of multiple births indicates that there was a strong positive relationship between multiple-birth status and infant mortality (Table 2 – see additional file 2). Children born multiple-birth were about two times as likely to die in infancy as those born singleton (hazard ratio [HR] = 2.00; 95% confidence interval [CI]: 1.43, 2.81). The Unadjusted models show that the infant mortality was significantly associated with delivery by a health-care professional, mother's BMI, mother's education, safe source of drinking water, hygienic toilet facility, type of fuel used for cooking, urban/rural residence and geographic division. In the adjusted model, when all characteristics of the child and mother, household wealth status, availability of safe drinking water, availability of a hygienic toilet facility, type of fuel used for cooking, urban/rural residence and geographic divisions were controlled for, the relationship of multiple birth and infant mortality remains significant. With all child-, maternal-, household-specific and other factors controlled, children born multiple birth were more than twice as likely to die during infancy as infants born singleton (HR = 2.19; 95% CI: 1.50, 3.19).
In the adjusted model (Table 2 – see additional file 2), with multiple birth status and other factors controlled, children born to mothers with secondary education or more were less likely to die before reaching their first birthday than children of mothers with no education (HR = 0.51; 95% CI: 0.36, 0.72). Compared to children from the poorest households, infant from the richer households are less likely to die before their first birthday (HR 0.67; 95% CI: 0.47, 0.96). None of the other risk factors or confounders has a statistically significant effect on the risk of infant mortality.
Results of this study support claims that children born multiple births are more likely to die during the first year of life as children born singletons, independent of child's sex, birth order, pregnancy care and delivery care, maternal education and nutritional status, household access to clean water and sanitation, and other factors. It is important to note that the more fully adjusted model showed a higher estimated probability of children born multiple births not to survive beyond their first birthday than the unadjusted model. This illustrate that the adjusted model was more effective in predicting the risk of infant mortality among children born multiple births, which is supported theoretically. The association between multiple birth and infant mortality has been observed not only in developing countries [7-14] but also in developed countries [15-22].
One possible reason for this observed association is that multi-foetal pregnancy and multiple births including twins and higher order multiples such as triplets and quadruplets are high-risk pregnancy and birth. These high-risk births are frequently accompanied by a number of associated foetal and neo