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OBJECTIVE To evaluate the discrepancy between historical and more recent descriptions of the first stage of labour by testing whether the statistical techniques used recently (repeated-measures polynomial and interval-censored regression) were appropriate for detection of periods of rapid acceleration of cervical dilatation as might occur at the time of transition from a latent to an active phase of labour. DESIGN AND SETTING A simulation study using regression techniques. SAMPLE We created a simulated data set for 500 000 labours with clearly defined latent and active phases using the parameters described by Friedman. Additionally, we created a data set comprising 500 000 labours with a progressively increasing rate of cervical dilatation. METHODS Repeated-measures polynomial regression was used to create summary labour curves based on simulated cervical examinations. Interval-censored regression was used to create centimetre-by-centimetre estimates of rates of cervical dilatation and their 95th centiles. MAIN OUTCOME MEASURES Labour summary curves and rates of cervical dilatation. RESULTS Repeated-measures polynomial regression did not detect the rapid acceleration in cervical dilatation (i.e. acceleration phase) and overestimated lengths of labour, especially at smaller cervical dilatations. There was a two-fold overestimation in the mean rate of cervical dilatation from 4 to 6 cm. Interval-censored regression overestimated median transit times, at 4- to 5-cm cervical dilatation or when cervical examinations occurred less frequently than 0.5- to 1.5-hourly. CONCLUSION Repeated-measures polynomial regression and interval-censored regression should not be routinely used to define labour progress because they do not accurately reflect the underlying data. TWEETABLE ABSTRACT Repeated-measures polynomial and interval-censored regression techniques are not appropriate to model first stage of labour.

Background Abnormal fetal growth is a risk factor for perinatal mortality and morbidity. There is considerable debate about the choice and performance of growth charts to classify newborns as small or large for gestational age (SGA and LGA) as a proxy for the at-risk infants. Several international charts have been proposed to be adopted worldwide. We aim to evaluate the performance of commonly-used growth charts (including international INTERGROWTH-21st-standards) for predicting adverse outcomes among SGA and LGA babies. Methods A population cohort of 2.4 million singleton births (24+0–40+6 weeks) delivered in Australia, 2004–2013. Performance was evaluated by prevalence, relative risk and diagnostic accuracy for adverse outcome based on AUC. Results There was wide variation in SGA and LGA classification across charts. For example, compared to other charts, the INTERGROWTH-21st-standards classified half of the number of term-SGA babies (prevalence: 3-4% vs. 7-10%) (90th-centile), resulting in a smaller cohort of term-SGA at higher-risk of adverse outcome, and a larger LGA cohort with lower-risk of adverse outcome. All charts performed poorly for detecting adverse outcomes (AUC range for a composite outcome: 0.49-0.68) and across birthweight centiles. Conclusions Significant differences in the classification of newborns and the chart performance raises concerns about whether the INTERGROWTH-21st-standards are applicable to a multi-ethnic population such as Australia. Key messages Significant differences in the classification of newborns and the relatively poor predictive ability of growth charts means that over reliance on infant size alone may misclassify, and thus miss at-risk infants.

OBJECTIVE To evaluate three birth-weight (BW) standards (Australian population-based, Fenton and INTERGROWTH-21st ) and three estimated-fetal-weight (EFW) standards (Hadlock, INTERGROWTH-21st and WHO) for classifying small-for-gestational age (SGA) and large-for-gestational age (LGA) and predicting adverse perinatal outcomes in preterm and term babies. METHODS This was a nationwide population-based study conducted on a total of 2.4 million singleton births that occurred from 24 + 0 to 40 + 6 weeks' gestation between 2004 and 2013 in Australia. The performance of the growth charts was evaluated according to SGA and LGA classification, and relative risk (RR) and diagnostic accuracy based on the areas under the receiver-operating-characteristics curves (AUCs) for stillbirth, neonatal death, perinatal death, composite morbidity and a composite of perinatal death and morbidity outcomes. The analysis was stratified according to gestational age at delivery ( 90th centile) babies (24-25% vs 8-15%), resulting in a smaller cohort of term SGA at higher risk of adverse outcome and a larger LGA cohort at lower risk of adverse outcome. For term SGA (

Introduction: Birth weight reference charts based on historical infant birth weights have significant bias at preterm gestations because many preterm births are associated with abnormal growth. This study aims to determine whether more accurate birth weight charts can be constructed using data only from births that follow spontaneous onset of labour. Materials and Methods: This study was a single-centre retrospective observational study of 115,712 singleton live births. Births were classified as spontaneous or iatrogenic. Quantile regression was used to model the relationship between gestational age, sex, labour onset, and birth weight. Comparison was made of birth weights in the spontaneous and iatrogenic cohorts by gestation, and to existing ultrasound-based charts. Results: Birth weights of spontaneous and iatrogenic births were significantly different for gestational age at the median and 10th centiles. Iatrogenic preterm infants weighed less than their spontaneous preterm counterparts. Median and 10th centile birth weights derived from the spontaneous birth cohort closely approximate previous ultrasound-based curves. Discussion: Iatrogenic births are more likely to be associated with pre-existing growth disturbance. Inclusion of these data has significant impact on centile charts. Birth weight charts derived from only spontaneous births may offer a more accurate reference for clinicians.