Jane B. Ford

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.

Background Further efforts, informed by current data, are needed to reduce smoking during pregnancy. Aims To 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 Methods All 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. Results The overall smoking rate during pregnancy decreased from 14.5% in 1994 to 8.3% in 2016. 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. Conclusions Despite 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.

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 (PM_2.5) 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 PM_2.5 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 PM_2.5 (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.

Low haemoglobin has been linked to adverse pregnancy outcomes. Our study aimed to assess the association of haemoglobin (Hb) in the first 20 weeks of pregnancy, and restoration of low Hb levels, with pregnancy outcomes in Australia. Clinical data for singleton pregnancies from two tertiary public hospitals in New South Wales were extracted for 2011–2015. The relationship between the lowest Hb result in the first 20 weeks of pregnancy and adverse outcomes was determined using adjusted Poisson regression. Those with Hb <110 g/L were classified into ‘restored’ and ‘not restored’ based on Hb results from 21 weeks onwards, and risk of adverse outcomes explored with adjusted Poisson regression. Of 31,906 singleton pregnancies, 4.0% had Hb <110 and 10.2% had ≥140 g/L at ≤20 weeks. Women with low Hb had significantly higher risks of postpartum haemorrhage, transfusion, preterm birth, very low birthweight, and having a baby transferred to higher care or stillbirth. High Hb was also associated with higher risks of preterm, very low birthweight, and transfer to higher care/stillbirth. Transfusion was the only outcome where risk decreased with increasing Hb. Risk of transfusion was significantly lower in the ‘restored’ group compared with the ‘not restored’ group (OR 0.39, 95% CI 0.22–0.70), but restoration of Hb did not significantly affect the other outcomes measured. Women with both low and high Hb in the first 20 weeks of pregnancy had higher risks of adverse outcomes than those with normal Hb. Restoring Hb after 20 weeks did not improve most adverse outcome rates but did reduce risk of transfusion.

Introduction: There is debate about optimal management of pregnancies with a large‐for‐gestational age baby. A recent randomized controlled trial reported that early term induction of labor reduced cesarean section rates and infant morbidity. However, long term childhood outcomes have not been assessed. The aim of this study was to assess maternal, neonatal and child health and education outcomes for large‐for‐gestational age babies induced at 37‐38 weeks’ gestation.Material and methods: Population‐based record linkage study of term (37+ weeks), cephalic‐presenting singleton pregnancies with a large‐for‐gestational age baby in New South Wales, Australia, 2002‐2006. Linked birth, hospital, mortality and education data were used with at least 9 years follow up from birth. Exposure was induction of labor at 37‐38 weeks, compared to expectant management (spontaneous birth at ≥37 weeks and planned births at ≥39 weeks). Relative risks and 95% confidence intervals were estimated using Modified Poisson regression with robust variance.Results: Among 10 174 eligible pregnancies, 412 (4.0%) had an induction at 37‐38 weeks. Women in the induction group were less likely to have a cesarean section (RR: 0.65, 95% CI: 0.51‐0.82). Infants had higher rates of: low Apgar scores, birth trauma, neonatal jaundice and phototherapy use, and admission to special care nursery or neonatal intensive care than their expectantly managed counterparts. As children, they had higher rates of hospital admission (RR: 1.16, 95% CI: 1.04‐1.30) and special needs (RR: 1.98, 95% CI: 1.12‐3.50). However, by age 8 there was no difference in overall literacy and numeracy achievement.Conclusions: Although women who had an early term labor induction with large‐for‐gestational age were less likely to have a cesarean section, the increased risk of neonatal morbidities and additional healthcare utilization suggests the need for caution in early induction of large‐for‐gestational age babies before 39 weeks’ gestation.

While red blood cell transfusion rates have declined in most Australian medical specialties, obstetric transfusion rates have instead been increasing. Obstetric transfusions are mostly linked to postpartum haemorrhage, the rates of which have also increased over time. This study used two methodological approaches to investigate recent trends in obstetric transfusion in New South Wales (NSW) and the extent to which this was influenced by changing maternal and pregnancy characteristics. Linked birth and hospital records were used to examine rates of red blood cell transfusion in the postpartum period for mothers giving birth in NSW hospitals from 2005 to 2015. Logistic regression models were run to examine the contribution of maternal and pregnancy risk factors to changing rates of transfusion. Risk factors were divided into “pre-pregnancy” and “pregnancy related”. Crude and adjusted estimates of the effect of year of birth on obstetric transfusion rates were compared to assess the effect of risk factors on rates over time using two approaches. The first compared actual and predicted odds ratios of transfusion for each year. The second compared the observed increase in transfusion rate with that predicted after controlling for the risk factors. Among 935,659 births, the rate of obstetric transfusion rose from 13 per 1000 births in 2005 to 17 in 2011, and remained stable until 2015. From 2005 to 2015, postpartum haemorrhage increased from 74 to 114 per 1000 births. Compared with the rate in 2005, the available maternal and pregnancy characteristics only partially explained the change in rate of transfusion by 2015 (Method 1, crude odds ratio 1.39 (95% CI 1.25, 1.56); adjusted odds ratio 1.29 (95% CI 1.15, 1.45)). After adjustment for maternal and pregnancy characteristics, obstetric transfusion incidence was predicted to increase by 10.3%, but a 38.7% increase was observed (Method 2). Rates of obstetric transfusion have stabilised after a period of increase. The trend could not be fully explained by measured maternal and pregnancy characteristics with either of the two approaches. Further investigation of rates and maternal and clinical risk factors will help to inform and improve obstetric blood product use.

Introduction: There is a lack of evidence around the risk of transfusion following vaginal birth after cesarean (VBAC) compared with elective repeat cesarean section (ERCS); this is important for decision‐making about birth options. The aim of this study was to determine transfusion rates and risk of transfusion following intended VBAC and ERCS.Material and methods: Women with a primary cesarean who had a subsequent birth at term (≥37 weeks) in New South Wales between 2000 and 2012, were identified from the New South Wales Perinatal Data Collection. Blood transfusions were identified from linked hospital records. Women deemed ineligible for VBAC were excluded. Modified Poisson regression was used to determine transfusion risk associated with intended VBAC compared with ERCS. Intended mode of birth was classified as: (1) intended VBAC and vaginal birth, (2) intended VBAC and cesarean, (3) intended ERCS and (4) “intention uncertain”.Results: A total of 90 439 women were eligible for VBAC. Rates of transfusion were: 1.4% for intended VBAC and vaginal birth (n = 17 849); 1.2% for intended VBAC and cesarean (n = 7648); 0.3% for intended ERCS (n = 60 471); and 1.1% for “intention uncertain” (n = 4471). After adjusting for maternal and pregnancy characteristics, risk of transfusion was almost four times higher for women classified as intended VBAC than intended ERCS (adjusted risk ratio = 3.73, 95% confidence interval 2.90‐4.78).Conclusions: Following a prior primary cesarean, there was a higher risk of transfusion associated with attempting VBAC compared with ERCS. Though the absolute risk is small, it is important for women considering VBAC to choose birthing facilities with ready access to blood products.

The aim of this study was to determine the association between red blood cell transfusion and breastfeeding among women who have suffered a postpartum haemorrhage at birth taking into account post-birth haemoglobin concentrations. Among 15,451 maternities with postpartum haemorrhage in New South Wales public hospitals between 2007 and 2010, 1828 (12%) received a red cell transfusion. Among transfused women, 686 (38%) had haemoglobin concentration pre-transfusion < 70 g/L, 792 (43%) had 70–90 g/L, and 350 (19%) had > 90 g/L. Rates and adjusted relative risks (aRR) for breastfeeding at hospital discharge were as follows: for women with haemoglobin concentrations < 70 g/L following birth and received a transfusion, 78.6% were breastfeeding and the aRR of breastfeeding compared to untransfused women was 0.90 (99% confidence interval (CI) 0.86–0.95); for women with haemoglobin concentrations 70–90 g/L, 81.3% were breastfeeding, aRR 0.94 (99% CI 0.90–0.98); and for women with haemoglobin concentrations > 90 g/L, 80.9% were breastfeeding, aRR 0.94 (99% CI 0.88–1.00).