BACKGROUND:Exposure to high ambient temperatures has been shown to increase the risk of spontaneous preterm birth. Determining which maternal factors increase or decrease this risk will inform climate adaptation strategies.OBJECTIVES:This study aims to assess the risk of spontaneous preterm birth associated with exposure to ambient temperature and differences in this relationship between mothers with different health and demographic characteristics.METHODS:We used quasi-Poisson distributed lag non-linear models to estimate the effect of high temperature-measured as the 95th percentile of daily minimum, mean and maximum compared with the median-on risk of spontaneous preterm birth (23-36 weeks of gestation) in pregnant women in New South Wales, Australia. We estimated the cumulative lagged effects of daily temperature and analyses on population subgroups to assess increased or decreased vulnerability to this effect.RESULTS:Pregnant women (n = 916,678) exposed at the 95th percentile of daily mean temperatures (25ºC) had an increased risk of preterm birth (relative risk 1.14, 95% confidence interval 1.07, 1.21) compared with the median daily mean temperature (17℃). Similar effect sizes were seen for the 95th percentile of minimum and maximum daily temperatures compared with the median. This risk was slightly higher among women with diabetes, hypertension, chronic illness and women who smoked during pregnancy.CONCLUSIONS:Higher temperatures increase the risk of preterm birth and women with pre-existing health conditions and who smoke during pregnancy are potentially more vulnerable to these effects.

Abstract Background The 2014 Hazelwood coal mine fire was an unprecedented six-week severe smoke event in the Latrobe Valley, southeastern Australia. We aimed to determine whether maternal exposure to fine particulate matter (PM2.5) attributable to the event was associated with adverse fetal growth or maturity, including birthweight, small for gestational age, term low birthweight or preterm birth. Methods A cohort of babies born within the affected region was defined used administrative perinatal data. Maternal average and peak PM2.5 was assigned to residential address at time of delivery using a chemical transport model. Maternal, infant, meteorological and temporal variables were included in final linear and log-binomial regression models. Results 3,591 singleton livebirths were included; 763 were exposed in utero. Average PM2.5 exposure was 4.4 µg/m3 (IQR 2.1 µg/m3); average peak was 45.0 µg/m3 (IQR 35.1 µg/m3). No association between PM2.5 and fetal growth or maturity was observed. Gestational diabetes mellitus was an effect modifier in the relationship; babies of exposed gestational diabetic mothers were 97 grams heavier per 10 µg/m3 increase in average PM2.5 exposure (95%CI 74, 120 grams), compared to mothers without gestational diabetes. Conclusions Maternal PM2.5 exposure from a smoke event was not associated with adverse fetal growth or maturity. There was a trophic response amongst babies of mothers with gestational diabetes. Key messages Babies born to mothers with gestational diabetes may be more susceptible to the effects of smoke events on birthweight.

Research suggests that neonatal morbidity differs by maternal region of birth at different gestational ages. This study aimed to determine the overall and gestation-specific risk of neonatal morbidity by maternal region of birth, after adjustment for maternal, infant and birth characteristics, for women giving birth in New South Wales, Australia, from 2003 to 2016. The study utilized a retrospective cohort study design using linked births, hospital and deaths data. Modified Poisson regression was used to determine risk with 95% confidence intervals (95% CI) of neonatal morbidity by maternal region of birth, overall and at each gestational age, compared with Australian or New Zealand-born women giving birth at 39 weeks. There were 1 074 930 live singleton births ≥32 weeks’ gestation that met the study inclusion criteria, and 44 394 of these were classified as morbid, giving a neonatal morbidity rate of 4.13 per 100 live births. The gestational age-specific neonatal morbidity rate declined from 32 weeks’ gestation, reaching a minimum at 39 weeks in all maternal regions of birth. The unadjusted neonatal morbidity rate was highest in South Asian-born women at most gestations. Adjusted rates of neonatal morbidity between 32 and 44 weeks were significantly lower for babies born to East (adjusted relative risk [aRR] 0.65, 95% CI 0.62-0.68), South-east (aRR 0.76, 95% CI 0.73-0.79) and West Asian-born (aRR 0.93, 95% CI 0.88-0.98) mothers, and higher for babies of Oceanian-born (aRR 1.11, 95% CI 1.04-1.18) mothers, compared with Australian or New Zealand-born mothers. Babies of African, Oceanian, South Asian and West Asian-born women had a lower adjusted risk of neonatal morbidity than Australian or New Zealand-born women until 37 or 38 weeks’ gestation, and thereafter an equal or higher risk in the term and post-term periods. Maternal region of birth is an independent risk factor for neonatal morbidity in New South Wales.

Abstract Background To provide evidence for targeted smoking cessation policy, the aim of this study was to compare pregnancy outcomes of Aboriginal mothers who reported not smoking during pregnancy with those who reported smoking. Methods This population-based retrospective cohort study used linked data from routinely collected datasets. Not smoking during pregnancy was the exposure of interest among all New South Wales Aboriginal women who became mothers of singleton babies in 2010–2014. Unadjusted and adjusted relative risks (aRR) and 95%CIs from modified Poisson regression were used to examine associations between not smoking during pregnancy and maternal and perinatal outcomes including severe morbidity, inter-hospital transfer, perinatal death, preterm birth and small-for-gestational age. Population attributable fractions (PAFs) were calculated using adjusted relative risks. Results Compared with babies born to mothers who smoked during pregnancy, babies born to non-smoking mothers had a lower risk of all adverse perinatal outcomes including perinatal death (aRR=0.58, 95%CI 0.44–0.76), preterm birth (aRR=0.58, 95%CI 0.53–0.64) and small-for-gestational age (aRR=0.35, 95%CI 0.32–0.39). PAFs(%) were 27% for perinatal death, 26% for preterm birth and 48% for small-for-gestational-age. Compared with women who smoked during pregnancy (n = 8,919), those who did not smoke (n = 9,235) had a lower risk of being transferred to another hospital (aRR=0.76, 95%CI 0.66–0.89). Conclusions Babies born to women who did not smoke had much lower risks of all adverse perinatal outcomes. Key messages Between a quarter and a half of adverse perinatal outcomes in this population could potentially be prevented by an effective smoking cessation program.

Abstract Background Gaps exist concerning the relationship between maternal exposure to air pollution and birth outcomes, including the importance of low-level exposure. We aimed to explore the association between maternal exposure to ambient nitrogen dioxide (NO2) and fine particulate matter (PM2.5) and selected birth outcomes in Victoria, Australia. Methods We included all births occurring in Victoria, Australia from 1st March 2012 to 31st December 2015 using routinely collected government data. Outcomes included birthweight, small for gestational age (SGA), term low birth weight (tLBW), large for gestational age, and spontaneous preterm birth. Annual ambient NO2 and PM2.5 was assigned to maternal residence at birth. Maternal, meteorological and temporal variables were included in final log-binomial models. Results There were 285,594 births. Average annual ambient NO2 exposure was 6.0 parts per billion (ppb, IQR 3.9 ppb) and PM2.5 was 6.9 µg/m3 (IQR 1.3). IQR increases in ambient NO2 and PM2.5 were associated with fetal growth restriction, including decrements in birth weight, increased risk of SGA and tLBW. Women with gestational diabetes and hypertensive disorders of pregnancy had greater decrements in birth weight associated with exposure. Conclusions Maternal exposure to low-level ambient air pollution at levels below national and international air quality guidelines was associated with fetal growth restriction. Key messages Exposure to low-level ambient air pollution was associated with fetal growth restriction and women with obstetric complications were more susceptible. These findings may inform iterative revisions of air quality guidelines.

BACKGROUND:Breastfeeding beyond infancy (12 months) remains atypical in the United States, United Kingdom, Canada, and Australia, and the role of health care providers is unclear. The objective of this study was to compare women's perceptions of provider support and other factors affecting breastfeeding beyond infancy across countries, among women who had each successfully breastfed at least one child that long.METHODS:Women completed an online questionnaire distributed via La Leche League, USA (2013), about sources and ratings of support for breastfeeding for their oldest child who was breastfed at least 12 months and participant demographics. Multivariable log-binomial regression was used to compare ratings of health care provider support and the importance of 13 factors by country.RESULTS:Some similarities and many differences were observed across countries in support received from providers, whereas modest or no differences were observed in the importance women placed on factors like health benefits and enjoyment of breastfeeding. Of 59 581 women, less than half discussed their decision to breastfeed beyond infancy with their child's provider. United Kingdom women rated their comfort in discussing breastfeeding beyond 12 months with their providers and the support received as lower than United States women. Canadian women gave lower ratings than United States women, but inconsistently. Australian women rarely differed from United States women in their responses. Providers' recommendations were not important to the decision to breastfeed beyond infancy, especially for United Kingdom women.DISCUSSION:Rates of breastfeeding beyond infancy are low in these countries; improving provider support may help achieve global breastfeeding goals.

BackgroundLittle is known about the pregnancy outcomes of women who have had a stroke prior to a first pregnancy.AimTo identify a cohort of primiparous women giving birth to a single baby and compare the pregnancy outcomes of those with a pre‐pregnancy stroke hospitalisation record to those without a stroke hospitalisation record.Materials and MethodsRecord linkage study of all primiparous women aged 15–44 years with singleton pregnancies birthing in New South Wales, Australia from 2003 to 2015. Stroke was identified from 2001 to 2015 hospital data using International Classification of Diseases tenth Edition – Australian Modification codes I60–64. Women whose first hospital record of stroke was during pregnancy or <42 days after birth were excluded. Outcomes included diabetes or hypertension during pregnancy, mode of delivery, haemorrhage, severe maternal morbidity (validated composite outcome indicator), gestational age at birth, Apgar score (1 min < 7), and small‐for‐gestational age.ResultsOf 487 767 women with a first pregnancy, 124 (2.5/10 000) had a hospital record which included a pre‐pregnancy stroke diagnosis. Women with a stroke history were more likely to have an early‐term delivery (37–38 weeks; relative risk (RR) 1.49, 95% CI 1.17–1.90) and a pre‐labour caesarean (RR 2.83, 95% CI 2.20–3.63). There were no significant differences in other maternal or neonatal outcomes.ConclusionThis is the largest reported study of pregnancy and birth outcomes for women with a history of stroke. With the exception of pre‐labour caesarean, there were no differences in pregnancy outcomes for women with a history of stroke compared with women with no history of stroke.

Abstract Background In 2014, the Hazelwood coal mine fire was an unprecedented six-week severe smoke event in the Latrobe Valley, southeastern Australia. We aimed to determine whether maternal exposure to fine particulate matter (PM2.5) attributable to coal mine fire smoke was associated with gestational diabetes mellitus (GDM), hypertensive disorders of pregnancy and abnormal placentation. Methods We defined a cohort of all births >20 weeks in the Latrobe Valley from 1 March 2012 - 31 Dec 2015 utilising administrative perinatal data. Average and peak PM2.5 was assigned to residential address at delivery using a chemical transport model. Maternal, meteorological and temporal variables were included in final log-binomial regression models. Results 3,612 singleton pregnancies were included; 766 were exposed to the smoke event. Average maternal PM2.5 exposure was 4.4 µg/m3 (IQR 2.1). Average peak PM2.5 exposure was 44.9 µg/m3 (IQR 35.0). An interquartile range increase in average and peak PM2.5 was associated with a 7% and 16% increased likelihood of GDM respectively (Average PM2.5 95%CI 1.03, 1.10; <0.0001; Peak PM2.5 95%CI 1.09, 1.22; <0.0001). No association for hypertensive disorders or abnormal placentation was observed. Conclusions This is the first study to examine obstetric complications relating to a discrete smoke event. These findings may guide the public health response to future similar events. Key messages Exposure to a smoke event was associated with an increased risk of GDM. The public health implications may be substantial with a changing climate.

BackgroundO Rh(D)− red blood cell (RBC) units can generally be transfused to most patients regardless of their ABO blood type and are frequently used during emergency situations. Detailed usage patterns of O Rh(D)− RBC units in obstetric populations have not been well characterised. With the introduction of patient blood management guidelines, historical usage patterns are important for providing comparative data.AimsTo determine how the use of O Rh(D)− RBC units in pregnant women differs between hospitals of different sizes and obstetric capabilities prior to patient blood management guidelines.MethodsData from 67 New South Wales public hospital blood banks were linked with hospital and perinatal databases to identify RBC transfusions during pregnancy, birth and postnatally between July 2006 and December 2010. RBC transfusions were divided into O Rh(D)− or other blood types. Hospitals were classified according to birth volume, obstetric capability and location, with transfusions classified by timing and diagnosis.ResultsOf the 12 078 RBC units transfused into pregnant women, 1062 (8.8%) were O Rh(D)−. Higher use of O Rh(D)− RBC units was seen in antenatal transfusions, preterm deliveries and in regional or smaller hospitals. There was wide variation in rates of O Rh(D)− RBC transfusion among hospitals.ConclusionsThe rate of O Rh(D)− RBC unit use in obstetrics was lower during the period assessed than the nationally reported usage. It is encouraging that O Rh(D)− RBCs were more commonly used in emergency or specialised situations, or in facilities where holding a large blood inventory is not feasible.

The Hazelwood coal mine fire in Victoria, Australia, was an unprecedented national outdoor air pollution event that covered the surrounding area in smoke and ash for 6 weeks in February and March 2014 (Figure 1). The severe smoke event caused considerable community concerns within the neighbouring town of Morwell and the broader Latrobe Valley community, situated 150 km east of the capital city of Melbourne. The Latrobe Valley is a regional setting known for mining and agricultural industries, characterised by relative socioeconomic disadvantage compared with the rest of the state. In response to these concerns, and following extensive community consultation, the Hazelwood Health Study was established to examine the long-term impacts of the mine fire (https://hazelwoodhealthstudy.org.au/). The Hazelwood Health Study involves multiple research streams focusing on various health outcomes and vulnerable groups. The Latrobe Early Life Follow-up (ELF) Study is a stream of the Hazelwood Health Study which aims to investigate the potential impacts of exposure to a severe outdoor air pollution event, as caused by the 2014 Hazelwood coal mine fire, on the health and development of children in the Latrobe Valley. Specific objectives are to explore: (i) obstetric and perinatal outcomes; (ii) parental reports of minor illnesses in young children; (iii) respiratory, vascular and immune function of children from 3 to 12 years of age; and (iv) medication use, health care attendance, education and developmental outcomes in childhood following in utero and early childhood exposure to smoke from the Hazelwood coal mine fire. We also aim to evaluate whether the persistence of smoke and ash pollutants in homes is a useful additional marker of exposure to mine fire emissions. Ethics statement Ethics approval was obtained from the Tasmania Health and Medical Human Research Ethics Committee (ref H0015033 and H0014875).

In May 2018, Scotland became the first country in the world to implement minimum unit pricing (MUP) for all alcoholic drinks sold in licensed premises in Scotland. The use of a Sunset Clause in the MUP legislation was a factor in successfully resisting legal challenges by indicating that the final decision on a novel policy would depend on its impact. An overarching evaluation has been designed and the results will provide important evidence to inform the parliamentary vote on the future of MUP in Scotland. The evaluation uses a mixed methods portfolio of in-house, commissioned, and separately funded studies to assess the impact of MUP across multiple intended and unintended outcomes related to compliance, the alcoholic drinks industry, consumption, and health and social harms. Quantitative studies to measure impact use a suitable control where feasible. Qualitative studies assess impact and provide an understanding of the lived experience and mechanism of change for key sub-groups. As well as providing important evidence to inform the parliamentary vote, adding to the international evidence on impact and experience of alcohol pricing policy across a broad range of outcomes, this approach to evaluating novel policy interventions may provide guidance for future policy innovations.

Background: The relationship between maternal exposure to air pollution and birth outcomes is not well characterised where ambient air pollution is relatively low. Objectives: We aimed to explore the association between maternal exposure to ambient nitrogen dioxide (NO2) and fine particulate matter (PM2.5) and a range of birth outcomes in Victoria, Australia. Secondary aims were to explore whether obstetric conditions, such as gestational diabetes mellitus (GDM) and hypertensive disorders of pregnancy, were effect modifiers in observed relationships. Methods: We included all singleton births occurring in Victoria, Australia from 1st March 2012 to 31st December 2015 using routinely collected government data. Outcomes included birth weight, small for gestational age (SGA), term low birth weight (tLBW), large for gestational age (LGA), and spontaneous preterm birth (sPTB). We estimated exposure to annual ambient NO2 and PM2.5 concentrations, assigned to maternal residence at time of birth. Confounders included maternal, meteorological and temporal variables. Multivariable linear regression and log-binomial regression were used for continuous and dichotomous outcomes, respectively. Results: There were 285,594 births during the study period. Average NO2 exposure was 6.0 parts per billion (ppb, median 5.6; interquartile range (IQR) 3.9) and PM2.5 was 6.9 mu g/m(3) (median 7.1, IQR 1.3). IQR increases in ambient NO2 and PM2.5 were associated with fetal growth restriction, including decrements in birth weight (NO2 beta - 22.8 g; 95%CI -26.0, -19.7; PM2.5 beta - 14.8 g; 95%CI -17.4, -12.2) and increased risk of SGA (NO2 RR 1.08; 95%CI 1.06, 1.10; PM2.5 RR 1.05; 95%CI 1.04, 1.07) and tLBW (NO2 RR 1.06; 95%CI 1.01, 1.10; PM2.5 RR 1.04; 95%CI 1.03, 1.08). Women with GDM and hypertensive disorders of pregnancy had greater decrements in birth weight in association with pollutant exposure. Discussion: In this exploratory study using an annual metric of exposure, maternal exposure to low-level ambient air pollution was associated with fetal growth restriction, which carries substantial public health implications.

BackgroundFurther efforts, informed by current data, are needed to reduce smoking during pregnancy.AimsTo describe trends in smoking during pregnancy and identify regions most likely to benefit from targeted smoking cessation interventions, in New South Wales (NSW), Australia.Materials and MethodsAll women who gave birth in NSW between 1994 and 2016 were included. Smoking status was identified from the Perinatal Data Collection. For births between 2012 and 2016, women were grouped into Local Health District (LHD) of residence, and smoking rates calculated. The impacts of a hypothetical smoking cessation intervention in four LHDs with (i) high smoking rates and (ii) high numbers of smokers, were compared.ResultsThe overall smoking rate during pregnancy decreased from 22.1% in 1994 to 8.3% in 2016. [Correction added on 13 August 2020, after first online publication: the overall smoking rate during pregnancy in 1994 has been corrected from 14.5% to 22.1%.]. The decrease was lowest among women living in the most socioeconomically disadvantaged areas (41%) and highest among those living in the most advantaged areas (83%). Between 2012 and 2016, over half the women who smoked during pregnancy lived in one of four LHDs. Only 1% of women reporting smoking during pregnancy resided in the LHD with the highest smoking rate (34.7%). A simulated intervention targeting only four regions showed greater effect on the statewide smoking rate when targeting LHDs with high numbers of smokers rather than high smoking rates.ConclusionsDespite decreases in rates of smoking during pregnancy, there was evidence of geographic clustering of smokers. The greatest reduction in overall smoking may come from interventions targeting the four LHDs with the highest number of smokers.

OBJECTIVE: To investigate subsequent birth rates, maternal and neonatal outcomes for women with a history of placenta accreta spectrum (placenta accreta, increta, and percreta). METHODS: A population-based record linkage study of women who had a first, second, or third birth in New South Wales from 2003 to 2016 was conducted. Data were obtained from birth and hospital records and death registrations. Women with a history of placenta accreta spectrum were matched to women without, on propensity score and parity, to compare outcomes with women who had similar risk profiles. Modified Poisson regression models were used to calculate adjusted relative risk (aRR) for a range of maternal and neonatal outcomes. RESULTS: We identified recurrent placenta accreta spectrum in 27/570 (4.7%, 95% CI 3.0-6.5%) of second and 9/119 (7.6%, 95% CI 2.8-12.3%) of third pregnancies after placenta accreta spectrum in the preceding birth, with an overall recurrence rate of 38/689 (5.5%, 95% CI 3.9-7.5%, compared with the population prevalence of 25.5/10,000 births (95% CI 24.6-26.4). Subsequent births after placenta accreta spectrum had higher risk of postpartum hemorrhage (aRR 1.51, 95% CI 1.19-1.92), transfusion (aRR 2.13, 95% CI 1.17-3.90), cesarean delivery (aRR 1.19, 95% CI 1.02-1.37), manual removal of placenta (aRR 6.92, 95% CI 3.81-12.55), and preterm birth (aRR 1.43, 95% CI 1.03-1.98), with lower risk of small for gestational age (aRR 0.64, 95% CI 0.43-0.96), compared with similar-risk births. CONCLUSION: Women with a history of placenta accreta spectrum have increased risk of maternal morbidity, preterm birth, and placenta accreta spectrum in the subsequent pregnancy compared with similar-risk women with no previous placenta accreta spectrum, although the absolute risks are generally low. These findings may be used to inform counseling of women on the risks of future pregnancies.

Introduction Severe morbidity rates in neonates can be estimated using diagnosis and procedure coding in linked routinely collected retrospective data as a cost-effective way to monitor quality and safety of perinatal services. Coding changes necessitate an update to the previously published composite neonatal adverse outcome indicator for identifying infants with severe or medically significant morbidity. Objectives To update the neonatal adverse outcome indicator for identifying neonates with severe or medically significant morbidity, and to investigate the validity of the updated indicator. Methods We audited diagnosis and procedure codes and used expert clinician input to update the components of the indicator. We used linked birth, hospital and death data for neonates born alive at 24 weeks or more in New South Wales, Australia (2002-2014) to describe the incidence of neonatal morbidity and assess the validity of the updated indicator. Results The updated indicator included 28 diagnostic and procedure components. In our population of 1,194,681 live births, 5.44% neonates had some form of morbidity. The rate of morbidity was greater for higher-risk pregnancies and was lowest for those born at 39-40 weeks' gestation. Incidence increased over the study period for overall neonatal morbidity, and for individual components: intravenous infusion, respiratory diagnoses, and non-invasive ventilation. Severe or medically significant neonatal morbidity was associated with double the risk of hospital readmission and 10 times the risk of death within the first year of life. Conclusion The updated composite indicator has maintained concurrent and predictive validity and is a standardised, economic way to measure neonatal morbidity when using population-based data. Changes within individual components should be considered when examining longitudinal data.

The relationship between maternal exposure to ambient air pollution and pregnancy complications is not well characterized. We aimed to explore the relationship between maternal exposure to ambient nitrogen dioxide (NO2) and fine particulate matter (PM2.5) and hypertensive disorders of pregnancy, gestational diabetes mellitus (GDM) and placental abruption. Using administrative data, we defined a state-wide cohort of singleton pregnancies born between 1 March 2012 and 31 December 2015 in Victoria, Australia. Annual average NO2 and PM2.5 was assigned to maternal residence at the time of birth. 285,594 singleton pregnancies were included. An IQR increase in NO2 (3.9 ppb) was associated with reduced likelihood of hypertensive disorders of pregnancy (RR 0.89; 95%CI 0.86, 0.91), GDM (RR 0.92; 95%CI 0.90, 0.94) and placental abruption (RR 0.81; 95%CI 0.69, 0.95). Mixed observations and smaller effect sizes were observed for IQR increases in PM2.5 (1.3 µg/m3) and pregnancy complications; reduced likelihood of hypertensive disorders of pregnancy (RR 0.95; 95%CI 0.93, 0.97), increased likelihood of GDM (RR 1.02; 95%CI 1.00, 1.03) and no relationship for placental abruption. In this exploratory study using an annual metric of exposure, findings were largely inconsistent with a priori expectations and further research involving temporally resolved exposure estimates are required.

Introduction Research suggests that neonatal morbidity differs by maternal region of birth at different gestational ages. This study aimed to determine the overall and gestation-specific risk of neonatal morbidity by maternal region of birth, after adjustment for maternal, infant and birth characteristics, for women giving birth in New South Wales, Australia, from 2003 to 2016. Material and methods The study utilized a retrospective cohort study design using linked births, hospital and deaths data. Modified Poisson regression was used to determine risk with 95% confidence intervals (95% CI) of neonatal morbidity by maternal region of birth, overall and at each gestational age, compared with Australian or New Zealand-born women giving birth at 39 weeks. Results There were 1 074 930 live singleton births >= 32 weeks' gestation that met the study inclusion criteria, and 44 394 of these were classified as morbid, giving a neonatal morbidity rate of 4.13 per 100 live births. The gestational age-specific neonatal morbidity rate declined from 32 weeks' gestation, reaching a minimum at 39 weeks in all maternal regions of birth. The unadjusted neonatal morbidity rate was highest in South Asian-born women at most gestations. Adjusted rates of neonatal morbidity between 32 and 44 weeks were significantly lower for babies born to East (adjusted relative risk [aRR] 0.65, 95% CI 0.62-0.68), South-east (aRR 0.76, 95% CI 0.73-0.79) and West Asian-born (aRR 0.93, 95% CI 0.88-0.98) mothers, and higher for babies of Oceanian-born (aRR 1.11, 95% CI 1.04-1.18) mothers, compared with Australian or New Zealand-born mothers. Babies of African, Oceanian, South Asian and West Asian-born women had a lower adjusted risk of neonatal morbidity than Australian or New Zealand-born women until 37 or 38 weeks' gestation, and thereafter an equal or higher risk in the term and post-term periods. Conclusions Maternal region of birth is an independent risk factor for neonatal morbidity in New South Wales.

Introduction The under-reporting of Aboriginal and Torres Strait Islander people on routinely collected health datasets has important implications for understanding the health of this population. By pooling available information on individuals' Aboriginal or Torres Strait Islander status from probabilistically linked datasets, methods have been developed to adjust for this under-reporting Objectives To explore different algorithms that enhance reporting of Aboriginal status in birth data to define a cohort of Aboriginal women, examine any differences between women recorded as Aboriginal and those assigned enhanced Aboriginal status, and assess the effects of using different reported populations to estimate within-group comparisons for Aboriginal people. Methods Three algorithms, with different levels of inclusiveness, were used to establish different study populations all of which aimed to include all singleton babies born to Aboriginal or Torres Strait Islander women residing in New South Wales, Australia between 2010 and 2014 and their mothers. The demographics of the four study populations were described and compared using frequencies and percentages. In order to assess the impact on research outcomes and conclusions of using study populations derived from different algorithms, estimates of the associations between smoking during pregnancy and selected perinatal outcomes were compared using rates and relative risks. Results Women included in the study population through enhanced reporting were older, less disadvantaged and more commonly resided in urban areas than those recorded as Aboriginal in the birth data. Although rates of smoking and some perinatal outcomes differed between the different study populations, the relative risks of each outcome comparing smoking and non-smoking Aboriginal mothers were very similar when estimated from each of the study populations. Conclusions This work provides evidence that estimates of within-group relative risks are reliable regardless of the assumptions made for establishing the study population through the enhanced reporting of indigenous peoples.

Background Evidence suggests that the trend toward early planned births observed among singletons may be evident among twin pregnancies. Aims To describe trends in gestational age at birth, pregnancy characteristics, neonatal morbidity and mortality among twin pregnancies. Materials and Methods Population‐based data linkage study of twin births of ≥30 weeks of gestation without a major congenital anomaly born in 2003–2014 in New South Wales (NSW), Australia. Linked pregnancy and birth, hospital and mortality data were used. Generalised linear regression was used to assess linear trends. Risk difference (RD) and 95% confidence intervals were estimated. Results Among 28 076 eligible twin births (14 038 pregnancies), 49% of births occurred prior to 37 weeks and 69% of births were planned (pre‐labour caesarean or induction of labour). There were increases over time in the proportion of twin births at preterm gestations (30–34 weeks (RD 2.1, 95% CI 0.1, 4.0), 35–36 weeks (RD 7.5, 95% CI 5.4, 9.7)) and in the rates of planned births (pre‐labour caesarean (RD 6.4, 95% CI 4.0, 8.8), induction (RD 4.6, 95% CI 2.6, 6.6)). There was no significant change in stillbirth or neonatal death rates, but there was an increase in neonatal morbidity over the study period. Concurrently, there were increases in the prevalence of gestational diabetes; and decreases in pregnancy hypertension, assisted reproductive technology use, small‐for‐gestational age and birthweight discordance. Conclusions Gestational age at birth among twin births is decreasing and birth intervention is increasing. There are increasing rates of neonatal morbidity, but no overall change in perinatal mortality.