sional assistance at delivery. Twenty-one per cent of children were first order births, and 49% were fourth or higher order births. Only 9% of the births were to mothers aged 13–17, about 36% and 40% were to mothers' aged 18 – 24 and 25–34 years respectively, and the remaining 14% to mothers aged 35–48 years. Only 12% of the births were to undernourished mothers (BMI < 18.5 kg/m2), more than half (51%) of the births were to illiterate mothers. Consistent with higher fertility in the poorer households, 44% of children were born in the poorest 40% households, and 17% were born in the richest 20% households. Only (26%) of children were born in households with safe sources of drinking water. Most of the children (87%) were in households without a hygienic toilet facility. Similarly, most of the children (79%) were in households using high pollution fuels (firewood or straw) for cooking. Seventy-one per cent of births were in rural areas. By geographic division, more than one-third (35%) of the births were in North West, 24% were in North East, 14% were in North Central, 13% were in South South, 9% were in South West, and only 6% were in South East
On average, more than one in every 10 children born in Nigeria (101 per 1000 live births) does not survive to their first birthday. The infant mortality rate was very high among the multiple birth children – 236 per 1000 live births compared with 95 per 1000 live births among the singletons. The infant mortality rate was also higher among boys (107) than among girls (95). Mothers who received professional assistance at delivery were associated with lower infant mortality rate. There was a U-shaped relationship between infant mortality rate and childbirth order. Children were born to the older mothers (35–48 years old) were at greater risk of infant mortality. As expected infant mortality rate was strongly negatively associated with mother's educational status.
The probability of death before 12 months of age for children born in the poorest 20% households was greater than children 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 relations