Intrapartum risk factors for newborn encephalopathy: the Western Australian case-control study

Objective To identify intrapartum predictors of newborn encephalopathy in t erm infants. Design Population based, unmatched case-control study. Setting Metropolitan area of Western Australia-June 1993 to September 1995. Subjects All 164 term infants with moderate or ne newborn encephalopathy; 4 00 randomly selected controls. Main outcome measures Adjusted odds ratio estimates. Results The birth prevalence of moderate or severe newborn encephalopathy v ias 3.8/1000 term live births. The neonatal fatality was 9.1%. Maternal pyr exia (odds ratio 3.82), a persistent occipitoposterior position (4.29), and an acute intrapartum event (4.44) were all risk factors for newborn enceph alopathy. More case infants than control infants were induced (41.5% and 30 .5%, respectively) and fewer case infants were delivered by caesarean secti on without labour (3.7% and 14.5%, respectively). Operative vaginal deliver y (2.34) and emergency caesarean section (2.17) were both associated with a n increased risk. There was an inverse relation between elective caesarean section (0.17) and newborn encephalopathy. After application of a set of co nsensus criteria for elective caesarean section only three (7%) eligible ca se mothers compared with 33 (65%) eligible control mothers were sectioned e lectively. Of all the case infants, 113 (69%) had only antepartum risk fact ors for newborn encephalopathy identified; 39 (24%) had antepartum and intr apartum factors; eight (5%) had only intrapartum factors; and four (2%) had no recognised antepartum or intrapartum factors. Conclusions The causes of newborn encephalopathy are heterogeneous and many relate to the antepartum period. Elective caesarean section has an inverse association with newborn encephalopathy. Intrapartum hypoxia alone account s for only a small proportion of newborn encephalopathy. These results ques tion the view that most risk factors for newborn encephalopathy lie in the intrapartum period.