Severity and persistence of asthma and mental health: a birth cohort study.

BACKGROUND: The goal of the current study was to investigate asthma and mental health among youth in the community, and to consider the role of asthma severity and persistence in this link. Method Data were drawn from the Raine Study, a population-based birth cohort study in Western Australia. Logistic regression models and generalized estimating equations were used to examine the relationship between asthma at age 5 years and the range of internalizing and externalizing mental health problems at ages 5-17 years. Analyses were stratified by asthma severity and persistence, and adjusted for a range of potential confounders. RESULTS: More severe and persistent asthma at age 5 was associated with significantly increased odds of affective, anxiety, somatic, oppositional defiant and conduct problems at ages 5-17. Mild asthma and remitted asthma were not associated with heightened vulnerability to mental disorders. CONCLUSIONS: Our results suggest that youth with symptomatic asthma are more likely to suffer from a wide range of mental health problems, and that the likelihood of mental health problems appears to increase as a function of asthma severity. Youth with poorly controlled and/or more severe and persistent asthma may be considered a vulnerable group who might benefit from mental health screening in clinical, school and community settings.

Low-moderate prenatal alcohol exposure and risk to child behavioural development: a prospective cohort study.

OBJECTIVE: To examine the association of fetal alcohol exposure during pregnancy with child and adolescent behavioural development. DESIGN: The Western Australian Pregnancy Cohort (Raine) Study recruited 2900 pregnancies (1989-91) and the 14-year follow up was conducted between 2003 and 2006. SETTING: Tertiary obstetric hospital in Perth, Western Australia. POPULATION: The women in the study provided data at 18 and 34 weeks of gestation on weekly alcohol intake: no drinking, occasional drinking (up to one standard drink per week), light drinking (2-6 standard drinks per week), moderate drinking (7-10 standard drinks per week), and heavy drinking (11 or more standard drinks per week). Methods Longitudinal regression models were used to analyse the effect of prenatal alcohol exposure on Child Behaviour Checklist (CBCL) scores over 14 years, assessed by continuous z-scores and clinical cutoff points, after adjusting for confounders. MAIN OUTCOME MEASURE: Their children were followed up at ages 2, 5, 8, 10 and 14 years. The CBCL was used to measure child behaviour. RESULTS: Light drinking and moderate drinking in the first 3 months of pregnancy were associated with child CBCL z-scores indicative of positive behaviour over 14 years after adjusting for maternal and sociodemographic characteristics. These changes in z-score indicated a clinically meaningful reduction in total, internalising and externalising behavioural problems across the 14 years of follow up. CONCLUSIONS: Our findings do not implicate light-moderate consumption of alcohol in pregnancy as a risk factor in the epidemiology of child behavioural problems.

Trends in mode of delivery during 1984-2003: can they be explained by pregnancy and delivery complications?

OBJECTIVES: To describe trends in mode of delivery, to identify significant factors which affected mode of delivery, and to describe how these factors and their impact have changed over time. DESIGN: Total population birth cohort. SETTING: Western Australia 1984-2003. PARTICIPANTS: The analysis was restricted to all singleton infants delivered at 37-42 weeks of gestation with a cephalic presentation (n = 432,327). METHODS: Logistic regression analyses were undertaken to estimate significant independent risk factors separately for elective and emergency caesarean sections compared with vaginal delivery (spontaneous and instrumental), adjusting for potential confounding variables. MAIN OUTCOME MEASURES: Trends in mode of delivery, demographic factors, and pregnancy and delivery complications. Estimated likelihood of elective caesarean section compared with vaginal delivery and emergency caesarean section compared with vaginal delivery. RESULTS: Between 1984-88 and 1999-2003, the likelihood of women having an elective caesarean section increased by a factor of 2.35 times (95% CI 2.28-2.42) and the likelihood of an emergency caesarean section increased 1.89 times (95% CI 1.83-1.96). These caesarean section rate increases remained even after adjustment for their strong associations with many sociodemographic factors, obstetric risk factors, and obstetric complications. Rates of caesarean section were higher in older mothers, especially those older than 40 years of age (elective caesarean section, OR 5.42 [95% CI 4.88-6.01]; emergency caesarean section, OR 2.67 [95% CI 2.39-2.97]), and in nulliparous women (elective caesarean section, OR 1.54 [95% CI 1.47-1.61]; emergency caesarean section, OR 3.61 [95% CI 3.47-3.76]). CONCLUSIONS: Our data show significant changes in mode of delivery in Western Australia from 1984-2003, with an increasing trend in both elective and emergency caesarean section rates that do not appear to be explained by increased risk or indication.

Adjustment for current weight and the relationship between birth weight and blood pressure in childhood.

OBJECTIVE: To determine the role of current weight in mediating the relationship between birth weight and blood pressure within the context of the 'fetal origins' hypothesis. DESIGN: Prospective cohort study of 2507 pregnant women and their singleton offspring, delivered live at term, in Perth, Western Australia between 1989 and 1992. The study commenced at 16 weeks gestation with serial weight and blood pressure measurements recorded through early childhood. RESULTS: Inverse associations were found between birth weight and systolic blood pressure at ages 1, 3 and 6. The effect of birth weight on systolic blood pressure at age 6 reached statistical significance and was increased fourfold in magnitude to -2.3 mmHg [95% confidence interval = (-3.3 to -1.3), P < 0.01] after adjustment for current weight. The interaction term for birth weight and current weight was not statistically significant. Including intermediate weights did not produce a statistically significantly better model but did increase the magnitude of the estimated regression coefficient of birth weight on blood pressure, and only the birth weight and current weight terms were significant CONCLUSIONS: Adjustment for current weight serves to highlight the relationship between birth weight and blood pressure in childhood. Nevertheless, birth weight, rather than birth weight adjusted for current weight, is still the relevant predictor of later blood pressure within the context of the 'fetal origins' hypothesis.

Placental weight and placental ratio as predictors of later blood pressure in childhood.

OBJECTIVE: A significant inverse relationship between blood pressure and birth weight is firmly established. This association may be the result of fetal adaptations to an adverse intrauterine environment. Further markers of intrauterine growth include the weight of the placenta and the placental ratio (the ratio of placental weight to birth weight). A number of studies suggest that a decreased placental weight or an elevated placental ratio may be independent risk factors for subsequent high blood pressure. The overall evidence for this is, however, inconclusive. The purpose of the present study was to clearly define the relationships between placental weight, placental ratio and subsequent blood pressure during childhood. DESIGN: Prospective cohort study of 2507 singleton children, born at term during 1989-1992. Blood pressures were recorded at ages 1, 3 and 6 years, using a semi-automated oscillometric device. RESULTS: Inverse relationships existed between both systolic and diastolic blood pressure and placental weight, adjusted for current weight at ages 1, 3 and 6 years. The relationships between placental weight and systolic blood pressure were statistically significant at ages 1 and 3 years. There was no consistent relationship between placental weight and later blood pressure within birth weight categories. No clinically or statistically significant association was seen between the placental ratio and either systolic or diastolic blood pressures at any age. CONCLUSIONS: Birth weight, rather than placental weight or their ratio, is the early life factor most importantly related to subsequent blood pressure in childhood.

Dietary folate and nonneural midline birth defects: no evidence of an association from a case-control study in Western Australia.

In a population-based case-control study of dietary folate and neural tube defects, information was collected by interview and self-administered questionnaires from the mothers of cases with only neural tube defects, from the mothers of matched control infants with defects other than neural tube defects, and from the mothers of matched live-born infants with no birth defects. The association of midline birth defects (excluding neural tube defects) with dietary folate intake in the first 6 weeks of pregnancy was assessed by restricting the analysis to the 59 mothers of infants with midline defects in the first control group and comparing them with their matched control infants in the second control group. The crude and adjusted odds ratios for dietary folate and for folic acid supplementation were close to one, and all confidence intervals embraced unity. These data do not provide evidence of an association between midline birth defects (excluding neural tube defects) and either dietary folate or folic acid supplementation.

Periconceptional vitamin supplementation and neural tube defects; evidence from a case-control study in Western Australia and a review of recent publications.

STUDY OBJECTIVE: The aim was to assess the association of neural tube defects with periconceptional vitamin supplementation. DESIGN: This was a matched, population based case-control study. SETTING: Western Australia, 1982-1984. PARTICIPANTS: Mothers of 77 cases (93% of those eligible) with isolated neural tube defects, mothers of 77 matched control infants with defects other than neural tube defects (control group I), and mothers of 154 liveborn, matched, control infants with no birth defects (control group II) participated in the study. MEASUREMENTS AND MAIN RESULTS: Information was collected by interview and self administered questionnaire. Crude and adjusted odds ratios (and their 95% confidence intervals) showed a small but non-significant protective effect of folate supplementation in comparisons with both control groups. The adjusted ratios for the three months before pregnancy were 0.69 (0.06, 8.53) with control group I, and 0.11 (0.01, 1.33) with control group II. In the first six weeks of pregnancy, the adjusted odds ratios were 0.70 (0.32, 1.52) with control group I and 0.74 (0.29, 1.88) with control group II. The odds ratios for vitamin supplementation of any kind were all very close to or greater than one, and all confidence intervals embraced unity. CONCLUSIONS: These data do not provide evidence of an association between periconceptional vitamin supplementation and neural tube defects, although a protective effect of folate supplementation cannot be excluded with confidence, due to the low power of the study. Of three other observational studies of vitamins and neural tube defects, two have shown an association. While further studies of this kind may be of value, evidence must now be sought from randomised controlled trials.

Prenatal ultrasound biometry related to subsequent blood pressure in childhood.

STUDY OBJECTIVE: To relate measures of fetal growth/size other than birth weight with subsequent blood pressure measured on the same individuals within the context of the "fetal origins of adult disease". DESIGN: A prospective cohort study in which measurements of fetal dimensions obtained by serial ultrasound imaging between 18 and 38 weeks gestation were analysed with reference to systolic blood pressure measurements on the offspring at age 6 years. SETTING: Perth, Western Australia. PARTICIPANTS: A subgroup of 707 eligible mother-fetus pairs from a cohort of 2876 pregnant women and their offspring. The number of mother-fetus pairs varied at each gestational age and by measurement of fetal dimension. Subsequent blood pressure recordings were obtained on approximately 300 of the offspring at age 6 years. MAIN RESULTS: The findings confirmed the inverse association between birth weight and systolic blood pressure at age 6. There was, also, an inverse relation between fetal femur length and systolic blood pressure at age 6, adjusted for current height. Furthermore, an inverse association was demonstrated between a statistically derived measure of fetal growth (conditional z score) between 18 and 38 weeks gestation and later systolic blood pressure at age 6. The effect sizes for all three relations were in the order of 1-2 mm Hg per standard deviation change. CONCLUSION: The mechanisms underpinning the "fetal origins" hypothesis may be operative early in pregnancy and may be reflected in the length of the fetal femur in early to mid-pregnancy.

The aetiology of cerebral palsy.

I have attempted to give an overview of the latest thoughts on the aetiology of the cerebral palsies. These motor disabilities are of continuing interest and their prevalence is rising, particularly in low birth weight preterm singletons and multiple births. The likely multiplicity of causes demands intelligent investigation probably in collaborative population data bases. Ultrasound and other scans may provide better data on both site and timing of neonatal brain damage. However these are more likely to have been done on cerebral palsied children who were preterm than on those born at term. There are currently no clear preventive messages except those relating to postnatal cerebral palsy or encouraging strategies to reverse the increases in multiple births. The challenges now are to obtain better data on the antenatal factors and on causal sequences which may be important. The Little Foundation is seeking to encourage such collaborative studies. Other suggestions from our workshop [14] included attempting to follow up those infants who have been participants in large randomised controlled trials (such as those evaluating surfactant) to the age when they can be confidently diagnosed as having cerebral palsy. If antenatal data have been collected on them they may form the basis for a cohort analysis relating risk to cerebral palsy occurrence, as well as to answer questions about whether the intervention influenced cerebral palsy occurrence.

Spastic cerebral palsy: changes in birthweight and gestational age.

The birthweight and gestational age frequency distributions for spastic cerebral palsy (CP) cases and their controls were obtained from the Western Australian CP register. Following the introduction of neonatal intensive care, spastic CP rates have fallen amongst heavier (greater than or equal to 2500 g) infants and remained steady or risen amongst low birthweight (LBW: less than 2500 g) infants. The expected bimodality of both the birthweight and gestational age distributions for spastic diplegia cases was obvious in these data. Marked peaks occurred at 1500 g and 31 weeks and 3000 g and 39 weeks. The numbers of heavier, term diplegics fell between 1961-1965 and 1971-1975, and thus there were proportionally more preterm LBW diplegics more recently. The reasons for the fall in the heavier diplegics need investigation. Spastic hemiplegic and quadriplegic cases were more like the controls but with distributions skewed to the left. More of these individuals were more recently small for gestational age (SGA: less than 2500 g and over 37 weeks gestation). This highlights the importance of intrauterine damage in these two groups of spastic CP individuals.

The epidemiological characteristics of unexplained antepartum stillbirths.

All antepartum stillbirths weighing 1000 g or more born in Western Australia from 1980 to 1983 were categorised as 'unexplained' or 'explained' based on information from Perinatal Death Certificates. Using data from hospital and doctors' antenatal records a number of variables in each stillbirth category were compared by unconditional logistic regression. Significant differences were observed between the two groups in medical disorders and abnormalities of pregnancy, thus confirming our classification system. Compared with mothers of 'explained' antepartum stillbirths, mothers of unexplained antepartum stillbirths tended to have younger ages at delivery and had associated lower parity, more antenatal visits to the medical practitioner, fewer hospital admissions, a greater chance of having received care by a general practitioner than by a specialist obstetrician and were of more advanced gestation at the time of diagnosis. The results of this study indicate that the epidemiological characteristics of pregnancies resulting in unexplained antepartum stillbirths differ from those resulting in explained antepartum stillbirths. This suggests that unexplained antepartum stillbirths are not merely the result of inadequate obstetrical management but consist of a series of fetal disease states which are not currently amenable to detection.

An analysis of sudden infant death syndrome in aboriginal infants.

The purpose of this case-control study was to identify antenatal and perinatal risk factors for sudden infant death syndrome (SIDS) in Aboriginal infants in Western Australia (WA). Cases were all Aboriginal infants born in WA from 1980 to 1990 inclusive and classified as dying from SIDS in WA. Controls consisted of a matched group and a random group both selected from liveborn Aboriginal infants born from 1980 to 1990. Multivariate modelling showed that SIDS in Aboriginal infants was strongly related to young maternal age (< 20 years, odds ratio (OR) = 2.89), high parity (parity > 3, OR = 4.40) and being small-for-gestational age (OR = 3.36) but was not associated with single marital status (OR = 0.95) or male sex (OR = 0.97). Although the study was based on routinely collected data, results do highlight some important groups for SIDS prevention. To gain further knowledge in terms of SIDS in Aboriginal infants, there is an urgent need to collect information concerning infant care practices in the Aboriginal community.

Maternal cigarette smoking during pregnancy, low birth weight and subsequent blood pressure in early childhood.

Given the widely acknowledged inverse relationship between birth weight and blood pressure, a raised blood pressure in the offspring of smoking mothers as compared to those whose mothers did not smoke, would be anticipated by virtue of the reduction in birth weight associated with smoking during pregnancy. The objective of the present study was to test the hypothesis that maternal cigarette smoking during pregnancy has an effect on blood pressure in childhood independent of its effect on birth weight. Data was obtained from a prospective cohort study of 1708 pregnant women and their singleton offspring, delivered live at term, in Perth, Western Australia, commenced at 16 weeks gestation with serial blood pressure measurements through early childhood. Statistically significant associations were found between maternal smoking during pregnancy and systolic blood pressure at age six, between birth weight and systolic blood pressure at ages three and six, and between maternal smoking during pregnancy and birth weight. The relationship between birth weight and blood pressure in early childhood differed significantly on the basis of maternal cigarette smoking or not during pregnancy. This differential relationship persisted after adjustment for the child's current weight and socio-economic status. We concluded that intra-uterine exposure to maternal cigarette smoking increased children's blood pressure at age one through to age six. This was not wholly attributable to an effect on birth weight or confounding of the association between birth weight and subsequent blood pressure by the child's current weight or socio-economic factors. Furthermore, maternal smoking during pregnancy does not account for the acknowledged elevation in blood pressure associated with low birth weight. The present study is an exploration of a possible causal pathway underlying the birth weight/blood pressure association rather than simply a confirmation of such an association which has been detailed in many other papers.

A matched cohort study of planned home and hospital births in Western Australia 1981-1987.

OBJECTIVE: to evaluate practice comparing planned home birth with planned hospital birth DESIGN: a retrospective analysis of a cohort who had planned to have a home birth compared with a matched hospital birth group SETTING: Western Australia (WA) PARTICIPANTS: all women (N = 976) who 'booked' to have a home birth 1981-1987 and 2928 matched women who had a planned hospital birth (singleton births only). MEASUREMENTS AND FINDINGS: women in the home birth group had a longer labour, were less likely to have had labour induced or to have had any sort of operative delivery. They were less likely overall to have had complications of labour, but more likely to have had a postpartum haemorrhage and more likely to have had a retained placenta. Babies in the home birth group were heavier and more likely to be post-term. They were less likely to have had an Apgar score below 8 at 5 minutes, to have taken more than 1 minute to establish respiration or to have received resuscitation. The crude odds ratio for planned home births for perinatal mortality was 1.25 (95% CI 0.44-3.55). Postneonatal mortality was more common in the hospital group. Planned home births were generally associated with less intervention than hospital births and with less maternal and neonatal morbidity, with the exception of third stage complications. Although not significant, the increase in perinatal mortality has been observed in other Australian studies of home births and requires continuing evaluation. KEY CONCLUSIONS: Planned home births in WA appear to be associated with less overall maternal and neonatal morbidity and less intervention than hospital births. IMPLICATIONS FOR PRACTICE: whether these observed differences in intervention and morbidity have any relationship to the small, non-significant increase in perinatal mortality could not be determined in this study. Continuing evaluation of home birth practice and outcome is essential.

Prenatal determinants of motor disorders.

Cerebral palsies (CP) are the commonest childhood motor disorders, originating in early childhood as a result of interference in the developing brain. Identifying prenatal factors in CP is a challenge because there is a considerable period of time (years) between the causal event(s) and diagnosis. Four fascinating "natural" situations provided a unique opportunity to identify and measure prenatal exposures in relation to motor disorders, thus establishing the unequivocal role of some factors. However, the majority of studies determining adverse reproductive effects of environmental factors require a retrospective case-control approach, which present considerable problems. Studies based on the Western Australian CP register suggest that prenatal factors singly or in complex sequences are more common as causes than those occurring perinatally or postnatally. In future, better diagnosis of motor disorders, use of sophisticated scientific techniques to identify markers of neuronal development and the accurate linkage of these findings to clinical patterns of motor dysfunction are required.

Trends in perinatal mortality and cerebral palsy in Western Australia, 1967 to 1985.

OBJECTIVE: To analyse the trends in stillbirths, neonatal deaths, and cerebral palsy in all infants born in Western Australia from 1967 to 1985. To relate these trends to changes in perinatal care, particularly in relation to avoidance of intrapartum asphyxia in term infants and the increased survival of low birthweight infants. DESIGN: Descriptive epidemiological study calculating population rates for perinatal deaths and cerebral palsy according to year of birth and birth weight. SETTING: Western Australia. SUBJECTS: All infants born after 20 weeks' gestation or weighing at least 400 g (live and stillborn). MAIN OUTCOME MEASURES: Stillbirths, neonatal deaths (from perinatal death certificates), and cerebral palsy (from a population based register). RESULTS: Overall stillbirth rates fell from 12.1/1000 total births in 1967-70 to 8.1 in 1983-5. Early neonatal mortality fell from 13.0/1000 live births to 4.4 over the same period whereas total cerebral palsy rates remained at around 2-2.5/1000 live births. Death rates fell in all birth weight categories, particularly in low birthweight infants between 1975 and 1985, the period when birthweight data were available. In contrast, cerebral palsy rates in infants under 1500 g rose significantly over this period (from 12.1 in 1968 to 64.9 in 1985). The rise was seen in all spastic categories, including severely and multiply handicapped children. CONCLUSIONS: Large increases in the use of interventions aimed at reducing birth asphyxia and handicaps had not (by 1985) resulted in lower rates of cerebral palsy. This suggests that birth asphyxia is not a major cause. The increased survival of low birthweight infants has resulted in more cerebral palsy in this group, due either to postnatal complications of immaturity or prenatal damage to the fetal brain. These findings have implications for planning perinatal care and for litigation for putative obstetric malpractice in cerebral palsy cases.

Genitourinary tract infections in pregnancy and low birth weight: case-control study in Australian aboriginal women.

OBJECTIVE: To investigate the association between genital and urinary tract infections in pregnant Aboriginal women and low birth weight. DESIGN: Retrospective case-control study controlling for potential confounding variables. SETTING: Western Australia from 1985 to 1987. SUBJECTS: All Aboriginal women (n = 269) who had given birth to singleton infants weighing 2250 g or less (cases), and 269 randomly selected Aboriginal women who had given birth to singleton infants weighing 3000 g or more (controls). MAIN OUTCOME MEASURES: Proportions of women in case and control groups who had had genital and urinary tract infections; odds ratios for low birth weight when genitourinary tract infection was present; population attributable fraction of low birth weight to genitourinary tract infection. RESULTS: At the time of delivery 51% of women in the case group (109/215) had genitourinary tract infections compared with 13% of controls (35/266). After controlling for potential confounding variables the odds ratio for giving birth to infants weighing 2250 g or less when genitourinary tract infection was present was 4.0 (95% confidence interval 2.3 to 7.0). The proportion of infants with low birth weight attributable to genitourinary tract infection in the whole population of Aboriginal women was 32% (95% confidence interval 17% to 49%). CONCLUSIONS: There was a strong association between low birth weight and the presence of genitourinary tract infections in Aboriginal women both during pregnancy and at the time of delivery. A community intervention trial of screening and treatment of genitourinary infections in this population is recommended.

Association between breast feeding and asthma in 6 year old children: findings of a prospective birth cohort study.

OBJECTIVES: To investigate the association between the duration of exclusive breast feeding and the development of asthma related outcomes in children at age 6 years. DESIGN: Prospective cohort study. SETTING: Western Australia. SUBJECTS: 2187 children ascertained through antenatal clinics at the major tertiary obstetric hospital in Perth and followed to age 6 years. MAIN OUTCOME MEASURES: Unconditional logistic regression to model the association between duration of exclusive breast feeding and outcomes related to asthma or atopy at 6 years of age, allowing for several important confounders: sex, gestational age, smoking in the household, and early childcare. RESULTS: After adjustment for confounders, the introduction of milk other than breast milk before 4 months of age was a significant risk factor for all asthma and atopy related outcomes in children aged 6 years: asthma diagnosed by a doctor (odds ratio 1.25, 95% confidence interval 1.02 to 1.52); wheeze three or more times since 1 year of age (1.41, 1.14 to 1.76); wheeze in the past year (1.31, 1.05 to 1.64); sleep disturbance due to wheeze within the past year (1.42, 1.07 to 1.89); age when doctor diagnosed asthma (hazard ratio 1.22, 1.03 to 1.43); age at first wheeze (1.36, 1.17 to 1.59); and positive skin prick test reaction to at least one common aeroallergen (1.30, 1.04 to 1.61). CONCLUSION: A significant reduction in the risk of childhood asthma at age 6 years occurs if exclusive breast feeding is continued for at least the 4 months after birth. These findings are important for our understanding of the cause of childhood asthma and suggest that public health interventions to optimise breast feeding may help to reduce the community burden of childhood asthma and its associated traits.

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

OBJECTIVE: To ascertain antepartum 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%. The risk of newborn encephalopathy increased with increasing maternal age and decreased with increasing parity. There was an increased risk associated with having a mother who was unemployed (odds ratio 3.60), an unskilled manual worker (3.84), or a housewife (2.48). Other risk factors from before conception were not having private health insurance (3.46), a family history of seizures (2.55), a family history of neurological disease (2.73), and infertility treatment (4.43). Risk factors during pregnancy were maternal thyroid disease (9.7), severe pre-eclampsia (6.30), moderate or severe bleeding (3.57), a clinically diagnosed viral illness (2.97), not having drunk alcohol (2.91); and placenta described at delivery as abnormal (2.07). Factors related to the baby were birth weight adjusted for gestational age between the third and ninth centile (4.37) or below the third centile (38.23). The risk relation with gestational age was J shaped with 38 and 39 weeks having the lowest risk. CONCLUSIONS: The causes of newborn encephalopathy are heterogeneous and many of the causal pathways start before birth.

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

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.