Queensland Perinatal Data Collection Research Articles

Identifying Longer-Term Health Events and Outcomes and Health Service Use of Low Birthweight CALD Infants in Australia

IntroductionApproximately one-third of all births in Australia each year are by culturally and linguistically diverse (CALD) women. CALD women are at an increased risk of adverse pregnancy and birth outcomes including prematurity and low birthweight. Infants born weighing less than 2500 g are susceptible to increased risk of ill health and morbidities such as cognitive defects including cerebral palsy, and neuro-motor functioning.MethodsAn existing linked administrative dataset, Maternity 1000 was utilized for this study which has identified all children born in Queensland (QLD), Australia, between 1st July 2012 to 30th June 2018 from the QLD Perinatal Data Collection. This has then been linked to the QLD Hospital Admitted Patient Data Collection, QLD Hospital Non-Admitted Patient Data Collection, QLD Emergency Department Data Collection, and Medicare Benefits Schedule and Pharmaceutical Benefits Scheme Claims Records between 1 and 2012 to 30th June 2019.ResultsCulturally and linguistically diverse infants born with low birthweight had higher mean and standard deviation of all health events and outcomes; potentially preventable hospitalisations, hospital re-admissions, ED presentations without admissions, and development of chronic diseases compared to non-CALD infants born with low birthweight.DiscussionResults from this study highlight the disparities in health service use and health events and outcomes associated with low birthweight infants, between both CALD and Australian born women. This study has responded to the knowledge gap of low birthweight on the Australian economy by identifying that there are significant inequalities in access to health services for CALD women in Australia, as well as increased health events and poor birth outcomes for these infants when compared to those of mothers born in Australia.

Time trends and projections in the prevalence of gestational diabetes mellitus in Queensland, Australia, 2009-2030: Evidence from the Queensland Perinatal Data Collection.

Gestational diabetes mellitus (GDM) is the fastest-growing type of diabetes in Australia. We aimed to assess the time trends during 2009-2018 and projections of GDM in Queensland, Australia up to 2030. The study data were from the Queensland Perinatal Data Collection (QPDC) and included data on 606 662 birth events with the births reported from at least 20 weeks gestational age or birth weight at least 400 g. Bayesian regression model was used to assess the trends in the prevalence of GDM. The prevalence of GDM increased from 5.47 to 13.62% from 2009 to 2018 (average annual rate of change, AARC = +10.71%). If the trend remains the same, the projected prevalence will increase to 42.04% (95% uncertainty interval = 34.77-48.96) by 2030. Observing AARC across different subpopulations, we found that the trend of GDM increased markedly among women living in inner regional areas (AARC = +12.49%), were non-Indigenous (AARC = +10.93%), most disadvantaged (AARC = +11.84%), aged either of two age groups (AARC = +18.45% and + 15.17% for <20 years and 20-24 years, respectively), were with obesity (AARC = +11.05%) and smoked during pregnancy (AARC = +12.26%). Overall, the prevalence of GDM has sharply increased in Queensland, and if this trend continues, about 42% of pregnant women will experience GDM by 2030. The trends vary across different subpopulations. Therefore, targeting the most vulnerable subpopulations is vital to prevent the development of GDM.

Association between severe cyclone events and birth outcomes in Queensland, Australia, 2008–2018: a population based retrospective cohort study

ObjectiveInvestigate an association between severe tropical cyclones (TCs) and birth outcomes in an Australian population. MethodsWe analysed over 600,000 singleton livebirths collected through the Queensland Perinatal Data Collection between 2008 and 2018. We estimated the odds ratios (ORs) of adverse birth outcomes using logistic multi‐level modelling. ResultsExposure to TCs in early pregnancy was associated with significantly higher odds of preterm births in affected compared to unaffected areas during the TC year [OR=1.28, 95%CI=1.11, 1.49, p=0.001] and slightly significant higher odds in affected areas during TC years compared to non‐TC years. Significantly higher odds of low birthweight births were associated with mid‐pregnancy exposure to cyclone Marcia [OR=1.62, 95%CI=1.00, 2.40, p=0.016] . ConclusionsFindings aligned with studies demonstrating an association between exposure to environmental stressors in early to mid‐pregnancy and adverse birth outcomes. Implications for public healthThere is limited research into TCs and perinatal health in Australia despite most of the population residing along coastlines and TCs presenting one of the nation's most devastating weather events. This study will inform public health practice and contribute to further research into mitigating environmental risks faced by pregnant women.

Making every birth count: Outcomes of a perinatal mortality audit program.

Stillbirth rates have shown little improvement for two decades in Australia. Perinatal mortality audit is key to prevention, but the literature suggests that implementation is suboptimal. To determine the proportion of perinatal deaths which are associated with contributing factors relating to care in Queensland, Australia. Retrospective audit of perinatal deaths≥34weeks gestation by the Health Department in Queensland was undertaken. Cases and demographic information were obtained from the Queensland Perinatal Data Collection. A multidisciplinary panel used the Perinatal Society of Australia and New Zealand (PSANZ) perinatal mortality audit guidelines to classify the cause of death and to identify contributing factors. Contributing factors were classified as 'insignificant', 'possible', or 'significant'. From 1 January to 31 December 2018, 65 deaths (56 stillbirths and nine neonatal deaths) were eligible and audited. Most deaths were classified as unexplained (51.8% of stillbirths). Contributing factors were identified in 46 (71%) deaths: six insignificant (all stillbirths), 20 possibly related to outcome (17 stillbirths), and 20 significantly (16 stillbirths). Areas for practice improvements mainly related to the care for women with risk factors for stillbirth, especially antenatal care. The PSANZ guidelines were applied and enabled a systematic approach. A high proportion of late gestation perinatal deaths are associated with contributing factors relating to care. Improving antenatal care for women with risk factors for stillbirth is a priority. Perinatal mortality audit is a valuable step in stillbirth prevention and the PSANZ guidelines allow a systematic approach to aid implementation and reporting.

Trends in neonatal resuscitation patterns in Queensland, Australia — A 10-year retrospective cohort study

ObjectivesTo describe the frequency of neonatal resuscitation interventions implemented for newborn babies in the state of Queensland over a 10-year period and determine if these changes suggest adherence to changes in Australian guidelines. Study designA population-based retrospective cohort study utilising the Queensland Perinatal Data Collection dataset. All liveborn babies ≥23 + 0 weeks + days gestation born between 1 July 2007 and 30 June 2017 were included except those for whom resuscitation was not attempted and those babies <25 + 0 weeks for whom it was unsuccessful. Trends in resuscitation were demonstrated using Loess regression. ResultsOf 618,589 eligible newborns,182,260 received any resuscitation manoeuvre (29.5%). The proportion receiving oxygen without assisted ventilation declined from 19.3% in 2007−08 to 5.6% in 2016−17. Upper airway suctioning also decreased. Assisted ventilation increased from 7.9% to 10.0% of all babies with the largest contribution from late preterm and term babies. The rate of endotracheal suctioning for meconium and the rate of narcotic antagonist use also declined. A greater proportion of babies received chest compressions (1.9–3.2 per 1000 babies) and adrenaline (epinephrine). Mortality decreased from 1.9 to 1.5 per 1000 babies in the cohort. ConclusionTen-year trends showed reduced use of oxygen or upper airway suctioning without assisted ventilation, reduced intubation to suction meconium, reduced use of narcotic antagonists and greater use of assisted ventilation suggesting appropriate practice change in response to Australian neonatal resuscitation guidelines. The increase in the use of chest compressions and adrenaline was unexpected and the reasons for it are unclear.

Access and outcomes of general practitioner obstetrician (rural generalist)-supported birthing units in Queensland.

ObjectiveTo describe characteristics and outcomes of women birthing within GP‐obstetrician (rural generalist) supported rural (level 3) obstetric units in Queensland.DesignRetrospective descriptive study.Setting21 GP‐obstetrician supported birthing units in Queensland.ParticipantsWomen (n = 3111) birthing from January 2017 to December 2017.Main outcome measuresPatient, pregnancy and labour characteristics and key maternal and neonatal outcomes routinely recorded in the Queensland Perinatal Data Collection and Queensland Hospital Admitted Patient Data Collection were compared to Queensland public hospital aggregate data.ResultsWomen birthing in rural maternity units were significantly more likely to be Aboriginal or Torrs Strait Islander (16% v 9%), < 20 years old (7% v 4%), term deliveries (96% v 91%), achieve spontaneous onset of labour (67% v 51%), and birth (71% v 60%) (p<0.001) compared with all Queensland public hospitals. They were significantly less likely to be nulliparous (36% v 40%), use pharmacological analgesia (65% v 69%), or have continuous electronic fetal monitoring in labour (54% v 66%) (p<0.001). Neonatal outcomes were comparable; with no significant difference in stillbirth rate between rural units and all Queensland public hospitals (4.8 v 7.3 per 1000 births). Precipitate delivery was the most common labour complication (36% v 33%) (p<0.001).ConclusionGP‐obstetrician (rural generalist) supported rural birthing units in Queensland provide important access for low and medium risk women to deliver locally, with strong indicators of quality and safety.

What are the costs associated with child and maternal healthcare within Australia? A study protocol for the use of data linkage to identify health service use, and health system and patient costs

IntroductionThe current literature in Australia demonstrates that there are variations in access and outcomes in perinatal care based on socioeconomic factors. However, little has been done looking at the level...

The association between third trimester multivitamin/mineral supplements and gestational length in uncomplicated pregnancies.

Widespread use of maternal micronutrient supplements have been correlated to gestational length and outcome in women predisposed to pre-eclampsia and preterm birth. However, research is yet to be conducted examining the influence of micronutrient supplements on outcomes at term in uncomplicated pregnancies. To analyse the relationship between third trimester micronutrient supplementation and gestation length at birth, demographics and maternal birthing outcomes in well women at term in a South East Queensland representative population. This research retrospectively analysed existing data pertaining to 427 uncomplicated, pregnancies birthing at the Gold Coast and Logan Hospitals using information gathered through the Environments for Healthy Living Study and Queensland perinatal data collection. Data were analysed using SPSS v20 by Chi square, ANOVA and regression analysis. Women in the third trimester taking individual zinc, folic acid or iron supplements in combination with a multivitamin were twice as likely to birth beyond 41 completed weeks (AOR 2.054, 95% CI 1.310-7.383, p=0.038) then those who did not take any supplement when controlled for established confounders. Non supplement users were found to experience a lower rate of post dates labour and requirements for induction (AOR 0.483, 95% CI 0.278-0.840, p=0.01). Length of gestation demonstrates significant associations with micronutrient supplementation practices. Well women consuming third trimester individual micronutrient supplements in addition to multivitamins experienced a longer gestation at term compared to women taking no micronutrients, increasing their risk for postdates induction of labour.

The effect of obesity on pregnancy outcomes among Australian Indigenous and non-Indigenous women.

To assess whether the effect of pre-pregnancy overweight or obesity on maternal complications and perinatal outcomes is modified by Indigenous status. Population-based study using de-identified aggregate data on pregnancies resulting in singleton births from Indigenous (n=13582) and non-Indigenous (n=241270) women from the Queensland Perinatal Data Collection, 1 July 2007 to 31 December 2011. Prevalence of maternal (gestational diabetes mellitus [GDM], hypertensive disorders of pregnancy [HDP]) and delivery (preterm birth, birthweight, Apgar score) outcomes by Indigenous status and their association with pre-pregnancy body mass index. In 57% of Indigenous pregnancies and 49% of non-Indigenous pregnancies, the mother was overweight, obese or severely obese. Prevalences of GDM, preterm birth and low birthweight were higher in Indigenous than non-Indigenous pregnancies. Overall rates of HDP were similar for Indigenous (5.1%) and non-Indigenous pregnancies (4.9%); however, rates were higher in normal-weight Indigenous pregnancies (4.0%) than in normal-weight non-Indigenous pregnancies (3.0%). We found that overweight or obesity was associated with higher prevalence of GDM, HDP, high birthweight and low Apgar score. However, the associations with HDP, preterm birth and low birthweight were modified by Indigenous status (P for interaction, <0.001 for all). Overweight or obesity accounted for significantly fewer cases of HDP in Indigenous versus non-Indigenous pregnancies (population attributable fraction, 30% v 41%). Maternal overweight or obesity is more common among Indigenous pregnancies, and Indigenous status may modify its association with pregnancy outcomes. Further research needs to explore the issue of increased insulin resistance and higher rates of HDP among normal-weight Indigenous women.

Gestational diabetes mellitus in Far North Queensland, Australia, 2004 to 2010: midwives' perinatal data most accurate source.

This study examines the accuracy of Gestational Diabetes Mellitus (GDM) case-ascertainment in routinely collected data. Retrospective cohort study analysed routinely collected data from all births at Cairns Base Hospital, Australia, from 1 January 2004 to 31 December 2010 in the Cairns Base Hospital Clinical Coding system (CBHCC) and the Queensland Perinatal Data Collection (QPDC). GDM case ascertainment in the National Diabetes Services Scheme (NDSS) and Cairns Diabetes Centre (CDC) data were compared. From 2004 to 2010, the specificity of GDM case-ascertainment in the QPDC was 99%. In 2010, only 2 of 225 additional cases were identified from the CDC and CBHCC, suggesting QPDC sensitivity is also over 99%. In comparison, the sensitivity of the CBHCC data was 80% during 2004-2010. The sensitivity of CDC data was 74% in 2010. During 2010, 223 births were coded as GDM in the QPDC, and the NDSS registered 247 women with GDM from the same postcodes, suggesting reasonable uptake on the NDSS register. However, the proportion of Aboriginal and Torres Strait Islander women was lower than expected. The accuracy of GDM case-ascertainment in the QPDC appears high, with lower accuracy in routinely collected hospital and local health service data. This limits capacity of local data for planning and evaluation, and developing structured systems to improve post-pregnancy care, and may underestimate resources required. Data linkage should be considered to improve accuracy of routinely collected local health service data. The accuracy of the NDSS for Aboriginal and Torres Strait Islander women requires further evaluation.

Pre‐pregnancy BMI: Costs associated with maternal underweight and obesity in Queensland

The economic costs of maternal obesity and underweight have not been described. We aim to assess the effect of maternal underweight and obesity on hospital utilisation and hospital costs. Data from the Queensland Perinatal Data Collection and Queensland Hospital Admitted Patient Data Collection were analysed for 2008. The sample included 37,912 Queensland resident mothers with a singleton pregnancy who gave birth in a public facility. Outcome measures were hospital length of stay (LOS) and hospital costs accrued during the birth admission and during pre- and postnatal admissions within 90days of the birth admission. There were 1,581 (4.2%) underweight, 17,175 (45.3%) normal weight, 10,155 (26.8%) overweight and 9,001 (23.7%) obese women. Maternal obesity was associated with significantly longer stays although effect sizes were modest (≤0.5days) and specific to women who delivered vaginally. LOS was significantly higher among babies born to underweight mothers when compared to those born to normal weight women. Maternal obesity was associated with a total increase of $5 million in mothers' hospital costs when compared to those amongst normal weight women; the corresponding figure for underweight mothers was $385,734. The total hospital costs for babies born to underweight women were $1.6 million higher than those born to mothers in the normal weight category. Maternal obesity was not associated with an increase in babies' hospital costs. Maternal obesity contributed to an increase in mothers' hospital LOS and hospitalisation costs. Maternal underweight contributed to an increase in babies' hospital costs.

Trends and determinants of caesarean sections births in Queensland, 1997–2006

The determinants of Queensland's rising caesarean section (CS) rate remain poorly understood because of the historical absence of standard classification methods. We applied the Robson Ten Group Classification System (RTGCS) to population-based data to identify the main contributors to Queensland's rising CS rate. The RTGCS was applied retrospectively to the Queensland Perinatal Data Collection. CS rates were described for all ten RTGCS groups using data from 2006. Trends were evaluated using data for the years 1997-2006. Public and private sector patients were evaluated separately. In Queensland, in 2006, CS rates were 26.9 and 48.0% among public and private sector patients, respectively. Multiparous women with a previous caesarean birth (Group 5) made the greatest contribution to the CS rate in both sectors, followed by nulliparous women who had labour induced or were delivered by CS prior to the onset of labour (Group 2) and nulliparous women in spontaneous labour (Group 1). CS rates have risen in all RTGCS groups between 1997 and 2006. The trend was pronounced among multiparous women with a previous caesarean delivery (Group 5), among women with multiple pregnancies (Group 8) and among nulliparous women who had labour induced or were delivered by CS prior to the onset of labour (Group 2). The CS rate in Queensland in 2006 was higher than in any other Australian state. The increase in Queensland's CS rates can be attributed to both the rising number of primary caesarean births and the rising number of repeat caesareans.

Adverse outcomes of labour in public and private hospitals in Australia

TO THE EDITOR: In their national analysis, Robson and colleagues found less favourable outcomes among term singleton babies born in public hospitals than in private hospitals. Most health services research is non-randomised, and it is unrealistic to expect studies such as this to be as internally valid as a randomised controlled trial. As noted by others, in the absence of randomisation, it is difficult to untangle the myriad differences between mothers, babies, and the care provided in private and public hospitals (ie, the results might be subject to confounding). Robson et al statistically accounted for the potential confounding effect of maternal smoking (although these data were only available for about half the mothers), age, Indigenous status, parity, diabetes, hypertension, rurality and method of birth. We replicated their analysis using the Queensland Perinatal Data Collection (July 2005 – December 2007), which included virtually complete data on maternal smoking. Our analysis of 124 300 term singleton babies gave an adjusted odds ratio (AOR) for perinatal mortality of 2.0 (95% CI, 1.4–2.7), which is similar to that reported by Robson et al. Using more detailed data from the Queensland dataset, we statistically adjusted for other potential confounders — including pre-existing and gestational diabetes, pre-existing and pregnancy-induced hypertension, pre-eclampsia, eclampsia, antepartum haemorrhage, anaemia , depression, urinary tract infection, low birthweight (< 2500 g), socioeconomic status (based on area of usual residence), alcohol and drug misuse, and artificial reproductive technology — and obtained an AOR of 2.1 (95% CI, 1.5–2.9). We are not implying that adding more and more variables to a statistical model is an appropriate way to account for confounding. Our aim is simply to show that Robson et al’s result is robust to statistical adjustment using the available data; this is not the same as saying the analysis is robust to confounding. We found that the higher perinatal mortality in public hospitals was greater for neonatal deaths (AOR, 3.1; 95% CI, 1.8– 5.6) than for stillbirths (AOR, 1.6; 95% CI, 1.0–2.4). Excluding lethal congenital anomalies did not materially change the result (AOR, 1.9; 95% CI, 1.3–2.8). We also stratified our analysis by level of hospital — tertiary referral (neonatal intensive care unit), base (special care nursery), and community — and obtained a similar twofold mortality excess in each stratum. Although perinatal mortality is uncommon among term singleton babies (1 in 1000 in private hospitals versus 2 in 1000 in public hospitals), any excess risk should be investigated and the reasons for it understood. The results from Robson et al’s article might be due to confounding, but they should not be dismissed and should be investigated with more detailed clinical data. Even if all the excess risk is due to confounding, explicit confirmation of this would be extremely useful. To this end, the Statewide Maternity and Neonatal Clinical Network in Queensland Health will undertake clinical review and classification of term singleton deaths according to national guidelines and collaborate with the Australian Maternity Outcomes Surveillance System (AMOSS) to enhance prospective monitoring of late gestation perinatal deaths nationally.

Trends in birth size and macrosomia in Queensland, Australia, from 1988 to 2005

The objectives of this study were to explore temporal changes in birth measures in Queensland, Australia, and examine whether secular trends are similar to those in other countries. This study used data from the Queensland Perinatal Data Collection, including singleton livebirths (n = 831 375) from 1988 to 2005. Recorded birthweight (BW, g), birth length (BL, cm), gestational age (weeks), maternal age, ethnic origin and calculated ponderal index (PI, kg/m(3)) were used. Temporal trends were assessed over the intervals 1988-2005 for BW and 2001-2005 for BW, BL and PI. Mean BW increased during the 17-year interval by approximately 1.9 g/year at a relatively low rate compared with reports from other countries. The proportion of high BW infants (> or = 4000 g) rose by 0.8% per year. Stratification by Indigenous status indicated that the increase in mean BW and prevalence of high BW was confined to non-Indigenous newborns only. The secular increase in BW was further modified by gestational age, and maternal age. The increase in BW was larger in term infants (4.2 g/year) than in preterm infants (1.8 g/year), and larger in infants of younger mothers than in those of older mothers (5.0 g/year vs. 3.1 g/year). There were no trends in mean BL and mean PI at birth from 2001 to 2005. In Queensland, mean BW increased moderately in the last 17 years, as did the proportion of high BW infants. The trend in rising BW remained after controlling for other perinatal characteristics. Birth measures per se and related trends differed by Indigenous status and warrant further investigation.

Post‐neonatal mortality by rurality and Indigenous status in Queensland

To compare post-neonatal mortality among urban and rural Indigenous babies in Queensland. Registrations of deaths at ages 28 days to 12 months were linked to routine data from the Queensland Perinatal Data Collection. Indigenous babies were 2.52 times more likely to die during the post-neonatal period than non-Indigenous babies (95% confidence interval: 1.99, 3.20). The differential remained when urban and rural areas were examined separately: the differential was 2.53 (1.81, 3.54) in urban areas and 2.26 (1.58, 3.23) in rural areas. The key demographic variable that determines post-neonatal mortality in Queensland is Indigenous status, not rurality. This has important policy implications because it means that interventions to reduce the disparity in mortality between Indigenous and non-Indigenous babies should be delivered in urban as well as rural areas. Better routine data are needed and in particular clinical classification of deaths, so that interventions can be monitored and avoidable factors identified.

Can a mortality excess in remote areas of Australia be explained by Indigenous status? A case study using neonatal mortality in Queensland

To assess the extent to which indigenous status confounds the association between remoteness and neonatal mortality in Queensland. We used routine data from the Queensland Perinatal Data Collection. Poisson regression modelling was used to assess confounding. Babies born to Indigenous mothers have mortality rates 2.42 times those of the rest of the population, regardless of whether they live in urban, rural or remote areas (95% CI 2.09-2.80). The babies of non-Indigenous women who live in remote areas have a low risk of neonatal death, similar to their rural and urban counterparts. In Queensland, the key demographic variable that determines neonatal mortality is indigenous status, not remoteness. Policymakers should not assume that an excess of a particular health problem in remote areas necessarily reflects equal disadvantage for all the Australians who live there.

Trends in birth rates for teenagers in Queensland, 1988 to 1997: an analysis by economic disadvantage and geographic remoteness

To investigate trends in the birth rate for teenagers in Queensland, stratified by geographic remoteness and economic disadvantage. This was an analysis of routine data for the period 1988 to 1997. The number of births were obtained from the Queensland Perinatal Data Collection. Population data (the denominators for the rates) were obtained from the Australian Bureau of Statistics. Economic disadvantage was based on place of usual residence of the mother. Because of differences in physical, social and psychological development, the data were analysed in three age groups: 13 to 14 years, 15 to 17 years and 18 to 19 years. Birth rates to teenagers who live in disadvantaged areas were 2 to 4 times higher than the rates for all of Queensland and 10 to 20 times higher than the rates in affluent areas. The trend analysis showed that the rates are decreasing in urban-affluent areas (about 2.5% per year), while they have remained stable, but extremely high in disadvantaged-remote areas, and are increasing (about 5% per year) in disadvantaged-urban areas. The relatively low and stable rates for all of Queensland have hidden marked variations in the trends for areas defined according to economic disadvantage and remoteness. The rates were especially high and showed no improvement over time in remote disadvantaged areas, which have a large indigenous population. In some areas of Queensland births to teenagers is a pressing problem, especially because it can perpetuate a cycle of limited educational opportunities, social isolation and reliance on welfare.

Is birthweight an appropriate health-outcome measure for Torres Strait Islander babies?

BackgroundAlthough Torres Strait Islanders (TSIs) are often combined with Aborigines, they are a distinct group and would prefer to be considered separately. The Queensland Perinatal Data Collection (QPDC) has been the only population-based, perinatal collection in Australia that has distinguished between Aboriginal and TSI mothers. It provided a unique opportunity to compare outcome measures based on birthweight in the TSI, Aboriginal and white populations. TSIs were of particular interest because recent research from overseas suggests that in groups with high rates of obesity and diabetes, birthweight is not a valid outcome measure. This is of concern because outcome measures based on birthweight have been proposed as a way of monitoring the neonatal health of Indigenous Australians. MethodsRetrospective analysis of 10 years of routine data from the QPDC. ResultsTSIs had a birthweight distribution similar to that of whites, but mortality rates similar to those of Aborigines. For birthweights between 2500g and 4000g, TSIs had mortality rates that were 2.5 times higher than those for whites (95%Cl: 1.3 to 4.2). ConclusionsAlthough birthweight is widely used, it is not necessarily a valid outcome measure in all populations. For TSIs, maternal conditions such as obesity and diabetes might cause changes in the uterine environment that produce heavier, but not healthier babies.

Does gestational age misclassification explain the difference in birthweights for Australian aborigines and whites?

After 34 weeks gestation, summary measures of location for birthweight (e.g means and centiles) increase more slowly for Australian Aborigines than for whites. A similar pattern has been observed for blacks in the US. This study tests whether the reported pattern is due to differential misclassification of gestational age. Simulation was used to measure the potential effect of differential misclassification of gestational age. Reported gestational age data were obtained from Queensland Perinatal Data Collection (QPDC). Estimates of the true distributions of gestational age were obtained by assuming various (plausible) types of misclassification and applying these to the reported distributions. Previous studies and data from the QPDC were used to help specify the birthweight distributions used in the simulations. At full term, the parameters of the birthweight distributions were robust to gestational age misclassification. At preterm, the 10th centiles were robust to misclassification. In contrast, the 90th centiles were sensitive to even minor misclassification. Extreme types of misclassification were required to remove the divergence in median birthweights for Aborigines and whites. Gestational age misclassification is an unlikely explanation for the reported divergence in average birth-weights for Aborigines and whites. The results might help with the interpretation of other between-population comparisons.