Obstetrical risk factors of ELBW

Preterm birth is the leading cause of perinatal morbidity and mortality worldwide [1]. It contributes to 70% of neonatal mortality and approximately half of long-term neurodevelopmental disabilities [2]. The obstetrics precursors leading preterm birth are delivery for maternal or fetal indications, spontaneous preterm labour with intact membranes and preterm premature rupture of membranes (pPROM) [3]. It is estimated that about 30-35% of all preterm births are indicated, 40-45% follow spontaneous preterm labour and 25-30% occur after pPROM [3]. Premature infants born at a gestational age of 32 weeks or less are obviously at greatest risk. The term “extreme low birthweight” (ELBW) is used to identify newborns with birthweight less than 1000 g. Although their prevalence is less than 1%, these newborns disproportionately account for nearly one-half of all perinatal deaths [4]. Antecedent risk factors for ELBW neonates, though geographically heterogeneous, include nulliparity and multiple gestations, each accounting for one-third and one-fourth of all births, respectively [5]. Spontaneous preterm labor precedes 34% of these deliveries and premature rupture of membranes in 25%. The pregnancy is complicated by hypertensive disease in about 20% of cases and bleeding and chorioamnionitis in 18%, respectively. Moreover, small for gestational age infants rate ranged from 16 to 20%. When the frequencies of these factors is compared between the United States and other countries, PROM rate is similar between the groups (25% vs. 26%, respectively), while others are not (chorioamnionitis: 18% vs. 37%, respectively). These variations may be due to publication bias, differences in maternal demographic characteristics, differences underlying burden of maternal or fetal illness, and/or differences in obstetrical practice patterns.