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

Abstract

Objective To identify intrapartum predictors of newborn encephalopathy in term 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 severe newborn encephalopathy; 400 randomly selected controls. Main outcome measures Adjusted odds ratio estimates. Results The birth prevalence of moderate or severe newborn encephalopathy was 3.8/1000 term live births. The neonatal fatality was 9.1%. Maternal pyrexia (odds ratio 3.82), a persistent occipitoposterior position (4.29), and an acute intrapartum event (4.44) were all risk factors for newborn encephalopathy. More case infants than control infants were induced (41.5% and 30.5%, respectively) and fewer case infants were delivered by caesarean section without labour (3.7% and 14.5%, respectively). Operative vaginal delivery (2.34) and emergency caesarean section (2.17) were both associated with an increased risk. There was an inverse relation between elective caesarean section (0.17) and newborn encephalopathy. After application of a set of consensus criteria for elective caesarean section only three (7%) eligible case mothers compared with 33 (65%) eligible control mothers were sectioned electively. Of all the case infants, 113 (69%) had only antepartum risk factors for newborn encephalopathy identified; 39 (24%) had antepartum and intrapartum 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 accounts for only a small proportion of newborn encephalopathy. These results question the view that most risk factors for newborn encephalopathy lie in the intrapartum period.

Risk factors associated with the development of perinatal asphyxia in neonates at Hospital Universitario del Valle, Cali, Colombia, 2010-2011

“…Some risk factors for the development of perinatal asphyxia have been reported to be preventable, and they were not always the same for the different populations under study; this difference in results suggests that these factors have not been fully extrapolated (9)(10)(11)(12).…”

Birth defects in children with newborn encephalopathy

“…We are confident that our control participants are a representative sample of Western Australian term live births (Badawi et al 1998b). This was further illustrated by the prevalence of birth defects in the control children which was the same as for the general Western Australian population of live-born term infants born 1993 to 1995 inclusive (4.7%; Bower et al 1997).…”

Synergy between antenatal exposure to infection and intrapartum events in causation of perinatal brain injury at term

“…Markers of, or risk factors for, materno-fetal infection such as prolonged rupture of membranes at term or intrapartum maternal pyrexia are strongly associated with evidence of neonatal cerebral dysfunction 2,9,10 . A recent meta-analysis found that among full-term infants there was a positive correlation between clinical chorioamnionitis and cerebral palsy (relative risk 4.7; 95% CI 1.3-16.2) 11 , while a similar relation exists between histologically diagnosed fetal chorioamnionitis and brain injury [odds ratio (OR) 13.2; 95% CI 1.2-144] 12 .…”

“…Yet in clinical practice this sequence of events is rare. Although normal labour often involves a degree of hypoxic stress, the incidence of moderate or severe encephalopathy after birth is low at less than 4 per 1000 live births 1,2 . This resistance to the effects of hypoxia is inversely related to maturity and is partly due to the presence of welldeveloped haemodynamic and metabolic compensatory mechanisms 8 .…”

“…The traditional belief that intrapartum hypoxia-ischaemia is the principal cause of both neonatal encephalopathy and cerebral palsy has been refuted by several large epidemiological studies 1 -4 . These have demonstrated the additional importance of a number of antepartum factors in the causal pathways of many cases of perinatal brain injury, including maternal thyroid disease, febrile illness and coagulation abnormalities 1,2,5 . In this article, we assess the evidence that both intrapartum hypoxia -ischaemia and materno-fetal infection can independently lead to term encephalopathy, but importantly, that a combination of the two could act in synergy, with fetal exposure to infection shortly before delivery leading to increased vulnerability to periods of hypoxic-ischaemic stress during labour.…”