Association of maternal and social characteristics with age-standardised birthweight

Secular trends of birthweight in a population of live-born, singletons, without congenital anomalies in Queensland, Australia

Objectives and importance

Maternal and family patterns are changing, and these changes can influence birthweight. Past research and organisational reports focus on short temporal timelines or broad trends, but trends across a longer temporal period are important. The aim of this study is to assess the trends in birthweight and maternal characteristics across a 19-year period using descriptive statistics.

Study type and methods

Birth records (n = 1,166,055) were obtained for a 19-year period (2000–2019) and a descriptive secular trend analysis was performed.

Results and conclusions

Mean birthweight trended down across the study period, while rates of large for gestational age births increased. This appears to be driven by a decrease in gestational age across the period. Maternal factors, such as smoking, BMI and Indigenous status, were found to be linked with changes in mean birthweight and the proportion of small for gestational age or large for gestational age. More babies were born to older women by the end of the study period. There was a sharp rise in gestational diabetes, and more large for gestational age births to these women. Over time, the large for gestational age births started to decline, suggesting better care practices for women with gestational diabetes.

The association of fractional cover, foliage projective cover and biodiversity with birthweight

INTRODUCTION

Environmental exposures can contribute both benefits and risks to human health. Maternal exposure to green space has been associated with improvements in birthweight, among other birth outcomes. Newer measures of green space have been developed, which allows for an exploration of the effect of different ground covers (green, dry and bare earth), as well as measures of biodiversity. This study explores the association of these novel green space measures with birthweight in a large birth cohort in Queensland, Australia.

METHODS

Birthweight was acquired from the routine health records. Records were allocated green space values for fractional cover, biodiversity and foliage projective cover. Directed acyclic graphs were developed to guide variable selection. Mixed-effects linear regression and generalised linear mixed-effects models were developed, with random intercepts for maternal residential locality and year of birth. Results are presented as standardised beta coefficients or odds ratios, with 95% confidence intervals.

RESULTS

An IQR increase of green cover (29.6 g, 95% CI 13.8-45.5) and foliage projective cover (26.0 g, 95% CI 10.8-41.3) are associated with birthweight in urban areas. An IQR increase in dry cover -34.4 g, 95% CI -60.4 to -8.4) and bare earth (-17.7 g, 95% CI -32.8 to -2.6) are associated with lower birthweight. Mothers living in rural areas had similar results, with an IQR increase in green cover (17.8 g, 95% CI 2.9-32.7) associated with higher birthweight, and bare earth (-27.7 g, 95% CI -45.7 to -9.7) was associated with lower birthweight. The biodiversity measure used in this study was not associated with any birthweight outcomes.

CONCLUSION

This study finds that the types of ground cover within the maternal residential locality are associated with small, but significant, changes in estimated birthweight, and these effects are not limited to urban areas.