The risk of perinatal death in Nigeria between 2008 and 2013 was significantly elevated by a range of risk factors, including babies born to older women (≥40 years of age), residing in rural areas, male gender, mother being obese (MBMI ≥30 kg/m2), having small or smaller birth size, birth through CS and having a fourth or higher birth order with a short birth interval ≤ 2 years after adjusting for necessary coexisting risk factors, including environmental-level factors.
The limitations of the current study are: (1) It is possible that over- or under-estimation may have affected PM risk estimates identified in this study because characteristics such neonatal jaundice, gestational age, sepsis or congenital anomalies, which were earlier found to be significantly related to early neonatal deaths in various hospital-based studies [10, 11] were not available for investigation. It is also possible that included characteristic such as perceived newborn size at birth by mothers may have impacted PM estimates because the rationale or criteria used was unclear. The perceived newborn size at birth by mothers could be limited by mother’s prior knowledge and experience of newborn. (2) Information on medical risk factors related to mothers during pregnancy, such as diabetes mellitus, hypertension and genitourinary tract infection [19, 20] previously found to be significantly associated with PM were lacking in the 2013 NDHS. (3) It has been argued that using early-pregnancy weight and height measurements yield more accurate BMI ; however, the current study assumed that MBMI at the time of survey was the same as that prior to the index birth, which may have biased our findings. (4) The number of newborn deaths and stillbirths may have been under-reported because only surviving mothers were interviewed. Additionally, mothers may have erroneously reported the gestational age when they had a stillbirth.
Notwithstanding these aforementioned weaknesses, this study used a nationally representative sample compared with earlier hospital-based studies in Nigeria [10, 11]. More importantly, this study suggested country-wide evidence on primary key factors associated with PM, which will enable healthcare policymakers to formulate uniform intervention programs to improve child survival across all six geopolitical zones and the Federal Capital Territory of Nigeria. In addition, we explored more data on many possible coexisting risk factors related to PM, including environmental-level factors, for sufficient statistical control.
Babies born to obese mothers had a 1.46 times greater risk of dying in the perinatal period than those having normal MBMI (18.5 ≤ MBMI ≤24.9). Similar findings were reported in earlier studies conducted in both developing and developed countries Nigeria , sub-Saharan Africa , Russia  and Sweden . An increased likelihood of perinatal deaths for babies born to obese mothers may be attributed to undiagnosed diabetes, gestational diabetes or prediabetic hyperglycaemia, hypertension and large-for-gestational-age birth, which were previously found to be associated with foetal or newborn deaths . This is supported by observational studies on maternal obese and pregnancy outcome in Nigeria, which found that diabetes mellitus, birth asphyxia, hypertensive disorders and macrosomia were significant medical risk factors associated with pregnant obese mothers in Nigeria . Another possible reason for the elevated perinatal deaths among obese mothers may be because they are ineffective at recognising decreased foetal movement, which often leads to foetal demise compared with underweight or normal weight mothers . The impact of obesity remains a crucial and amendable risk factor for PM. Effective maternal weight loss or control in obese women during pregnancy has been reported to reduce gestational diabetes, large-for-gestational-age birth and neonatal mortality .
The odds of perinatal deaths were greater in older mothers aged 40 years or higher compared with younger mothers. This finding is in contrast with earlier studies in Russia and Bangladesh [19, 30], which showed a statistically insignificant relationship between older mothers and perinatal deaths. A plausible explanation for these differing outcomes may be attributed to different definitions of PM, different populations, adjusted for different risk factors and the maternal age limits used. Nevertheless, other reports from both developing and developed countries also indicated that older mothers had a significantly elevated risk of perinatal death [31, 32]. The significantly increased perinatal deaths associated with older Nigeria mothers could be related to medical risk factors, such as antepartum haemorrhage, hypertension, operative vaginal delivery and gestational diabetes, which were previously reported to be associated with advanced maternal age [8, 26].
Babies perceived as small size after birth by their mothers remain a significant public health problem in Nigeria. A recent Nigerian population-based study suggested that nearly 30,000 newborn deaths in their first week of life were attributable to small-sized babies . The current study provides further evidence that smaller-than-average babies is a strong predictor of perinatal death in Nigeria, which is consistent with findings from previous studies [15, 33]. A plausible reason for the increased risk of perinatal deaths among the small-sized babies in Nigeria may be attributed to use of herbal medicines not prescribed  and poor diet intake during pregnancy often impact the foetus.
Furthermore, studies in low- and middle-income countries [35, 36] have reported that babies born to mothers residing in rural residences are more likely to experience PM compared with those in urban areas, and this study reaffirms the strong effects of rural residence on perinatal deaths. This may be due to inadequate access to healthcare facilities and maternal healthcare services. Most of the well-equipped hospitals and healthcare centres in Nigeria are typically found in urban and metropolitan areas, leading to a lower likelihood of perinatal deaths in urban areas. The risk of perinatal death was significantly greater for male babies than for female babies. This may be attributed to biological factors , such as late development of foetal lung in the first 7 days of life , resulting in more frequent respiratory diseases in male babies than in female babies.
Babies delivered by CS exhibited an almost threefold risk of perinatal death compared with vaginally born babies, which contradicts a previous study conducted in Swaziland . However, our result is consistent with a similar study performed in Mexico . An increased risk of CS may be linked to negative perceptions (e.g., fear, aversion) to CS  among pregnant women in Nigeria, which often leads to late referral to healthcare facilities for emergency CS after experiencing life-threatening complications at home or elsewhere. We also observed that babies of high birth order (fourth or higher) born with shorter birth intervals (≤2 years) had greater odds of dying during the perinatal period. This outcome is in line with an earlier study conducted in Kenya , which may be partly attributed to economic resource competition among infants and maternal depletion syndrome .
To accelerate progress towards reducing prenatal mortality in Nigeria by 2030, public health interventions are needed at the community and individual level. At the community level intervention, screening programmes during pregnancy should be encouraged among older mothers especially those who live in rural areas, At the individual level intervention, educating mothers on kangaroo mother care approach on small-sized or low birth weight newborns including those delievered by caesarean section. However, to achieve these goals, the political, economic and social obligation of the three tiers of government (Federal, State, and Local Goverment Area) are very important to substantially reduce perinatal deaths.