The proportion of LBW in our study was 18,2%, preterm was 11,9%, SGA based on all newborns was 7,51%, and SGA based on LBW was 41,43%, which was lower than that of Lee et al (2013) on Indonesia [2]. The different result came up probably because their study used Alexander's curve from the USA, for which the 1996 data were based on National Center of USA. Our study showed 1,2% preterm-SGA and 6,4% full term-SGA, which were similar to the results by Kristensen et al. (2007). However, it was different from Katz et al., which showed 3,4% preterm-SGA and 20,26% full-term SGA by using Alexander's above. Prevalence of SGA will decrease if a local population reference or a reference from low-middle countries is used [29].
Early neonatal death and neonatal death in our study were 31/1000 live births and 40/1000 live births consecutively, which was higher than Lee's result whose neonatal death was 15,9/1000 live births. We used the hospital-based data, whereas Lee used the population-based data [2]. In general, the neonatal condition in Sardjito hospital was more severe than that in Sleman hospital.
Preterm birth affects a smaller number of neonates than does SGA, but is associated with a higher mortality risk [28]. This study showed the largest number of preterm AGA with HR 1.75 ( 1.26-2.43).
SGA may be associated with increased risk of neonatal mortality [38, 39, 40, 41]. The risk increased further among infants of BW <3rd percentile [42]. Risks of stillbirth and neonatal death were two to three times higher in preterm SGA in low and medium income countries, except in the very high human development index. Term SGA was significantly associated with perinatal death irrespective of the categories [43]. Our study found preterm SGA with HR 1.99 (1.32-2.81) on early neonatal mortality death and HR 1.99 (1.39-2.85) on neonatal death. This was similar to that by Katz et al, which reported that the highest risk of neonatal mortality by gestational age and AGA-SGA was preterm SGA, with full-term AGA as a reference [4, 28].
Decreased neonatal mortality during 5-year-period suggested improvement of neonatal care in the health facilities, although SDG target had not been met. Improved quality of health providers, emergency equipment, and the development of neonatal intensive care units every 5 years showed the highest CMI in preterm SGA, preterm AGA, full-term SGA and full-term AGA respectively.
The symmetrical SGA group showed a consistently higher risk of death during the neonatal period [44,45]. The early neonatal mortality of symmetrical SGA infants with short crown-heel length was significantly greater than that of asymmetrical SGA infants with normal crown-heel length. However, a slightly but not significantly greater mortality was observed in asymmetrical SGA versus symmetrical SGA using Ponderal Index regardless of the method of SGA used [46]. Symmetrical SGA infants increased the risk of chronic lung disease, needed longer hospital stay, and had higher consumption of oxygen and continuous positive airway pressure than did asymmetrical SGA [45]. Our study showed the symmetrical SGA had higher HR on early and neonatal mortality than did asymmetrical SGA.
Asphyxia in our study, affected early neonatal mortality with HR 5.36 (4.38-6.55) and neonatal mortality with HR 4.45 (3.79-5.24). Another study reported that birth asphyxia deaths accounted for 30% of neonatal mortality [47]. Globally, the main direct causes of neonatal death are estimated to be preterm (28%), severe infections (26%), and asphyxia (23%) [48]. Indonesia Ministry of Health noted that asphyxia was responsible for 27% of neonatal mortality [26].
Preterm SGA infants have significantly higher mortality, higher risk of developing chronic lung disease, and longer hospital stay than premature AGA infants. Even the reduced risk of respiratory distress syndrome in infants born at ≥32 weeks of GA, (conferred possibly by intra-uterine stress leading to accelerated lung maturation) appears to be of transient effect and is counterbalanced by adverse effects of poor intrauterine growth on long term pulmonary outcomes such as chronic lung disease [31].
Also, mortality is significantly higher in preterm SGA with Odds ratio 3.1 and p =0.001 than in preterm AGA. Controlling gestational age, on the other hand, reduced the risk of respiratory distress syndrome [31]. Preterm SGA infants may be associated with increased risk of chronic lung disease and posed increased resource utilization [39,40,41, 45]. In the cohort of late preterm birth, there was no significant difference in the rate of composite respiratory morbidity between SGA and AGA neonates [49]. Our study reported that respiratory distress had HR 8.76 (6.95-11.0) on early neonatal mortality and HR 7.01 (5.08-8.47) on neonatal mortality.
The SGA neonates were not at an increased risk for early onset of neonatal sepsis [50,51]. While early onset of sepsis in the two groups did not pose differences, late onset of sepsis increased the risk of neonatal mortality [51]. Since sepsis was insignificant by multivariate analysis, it was not categorized into early and late.
This study also revealed that boys had HR 1.16 (1.03-1.32) on early neonatal mortality and HR 1.13 (1.01-1.26) on neonatal mortality. This was similar to the result of Tamayev’s study which reported boys and placental fetal inflammatory responses, and villitis of unknown etiology are independently associated with adverse neonatal outcome in SGA neonates [52].
Experience of maternal death may likely cause mothers to have infants with greater risks of mortality, and the survival trajectory of these children is far worse than that of mothers who do not die postpartum [53]. Our study showed mother’s death had HR 2,28 (1.71-3.05) on early neonatal death and HR 2.51 (1.96-3.21) on neonatal death. Another study reported that infants whose mothers died during delivery or shortly after were up to 7 times more likely to die within the first month of life than those whose mothers survived [54]. This highlights the importance of investigating how clinical care and socio-economic support programs can better address the need of orphans, both throughout the intra and postpartum periods, as well as over the life course [53].
Increased neonatal mortality through delivery at first health facility was 1,31 (!,12-1,53) and the same risk through delivery outside health facility increased by 2,07 (1,58-2,72). Similar result was found in early neonatal death. Another study revealed that infants born outside the hospital had a mortality risk with Odds ratio 1,7 (IK 95% 1,2-2,5) even though it had been adjusted to the perinatal risk and severity of the disease [55]. The result was consistent with the importance of encouraging tertiary hospital delivery for high risk infants [55,56]. Other studies demonstrated that preterm infants born in villages had a higher risk of neonatal mortality rate than those delivered in urban areas [57]. We therefore suggest that high risk antenatal fetus be referred to a tertiary hospital regionalization in order to reduce the possible harmful risks.
Percentage of PAR of LBW-SGA in our study revealed early neonatal death was 11,98% and neonatal death was 15,82%. It was lower than that of Sania et al whereby PAR of SGA infants on early neonatal death was 24,9% and neonatal death was 26,3%. The different result was because the study used Oken curve 1979 from the USA, which had not been updated and the study in Tanzania, Africa, which Sania mentioned as the limitation of the study. It showed lower gestational age, but higher percentage of PAR [33]. The percentage of PAR in our study was more than 11,98% for early neonatal death and 15,82% for neonatal death in population, in addition to more risks due to preterm. It is important information for health decision.
The power of the early neonatal mortality in SGA infants was 80,2 and neonatal was 97,23; and more than 80% was in the planning.
Weaknesses and strength of the study
The use of cohort retrospective was the weakness of our study, since it had potentials to miss some data. During the study, the data were recorded as soon as the baby was born. Re-check and re-examination were done to match all of the data. Trained administrators would entry the data into the database. The study consisted of only 1 tertiary hospital and 1 secondary district hospital due to limited funds and operational problems.
The number of sample was, however, much higher than the planned sample size. The high number of sample, on the other hand, was the strength of our study. Investigation was carried out for 20 years in order to analyse and compare the mortality every 5 years. Also, in this study, additional neonatal mortality in population was explored by using PAR percentage.