The impact of maternal prepregnancy impaired fasting glucose on preterm birth and large for gestational age: a large population-based cohort study

Abstract

The impact of maternal prepregnancy impaired fasting glucose on preterm birth and large for gestational age has been poorly understood. We aimed to estimate the impact of prepregnancy impaired fasting glucose defined by the World Health Organization cut point on the risk of preterm birth and large for gestational age and to investigate whether the World Health Organization cut point of impaired fasting glucose was appropriate for identifying women at risk of preterm birth and large for gestational age among the Chinese population. This was a retrospective cohort study of women from the National Free Preconception Health Examination Project with singleton birth from 121 counties/districts in 21 cities of Guangdong Province, China, from Jan. 1, 2013, to Dec. 31, 2017. Women were included if their prepregnancy fasting glucose was less than 7.0 mmol/L. The primary outcomes were preterm birth (gestational age <37 weeks), early preterm birth (gestational age <34 weeks), large for gestational age (birthweight by gestational age >90th percentile based on the international standards in the International Fetal and Newborn Growth Consortium for the 21st Century study), and severe large for gestational age (birthweight by gestational age >97th percentile). We calculated the adjusted risk ratio for impaired fasting glucose and a 1 standard deviation increase in fasting glucose. We included 640,469 women. Of these, 31,006 (4.84%) met the World Health Organization cut point for impaired fasting glucose, 32,640 (5.10%) had preterm birth and 7201 (1.12%) had early preterm birth, 45,532 (7.11%) had large for gestational age birth, and 16,231 (2.53%) had severe large for gestational age birth. Compared with women with normoglycaemia, women with prepregnancy impaired fasting glucose had a 7.0% higher risk of preterm birth (adjusted risk ratio, 1.07, 95% confidence interval, 1.02-1.12), 10.0% had a higher risk of large for gestational age (adjusted risk ratio, 1.10, 95% confidence interval, 1.06-1.14), and 17.0% had a higher risk of severe large for gestational age (adjusted risk ratio, 1.17, 95% confidence interval, 1.10-1.26). No significant association of prepregnancy impaired fasting glucose with early preterm birth was found. The association of prepregnancy impaired fasting glucose with preterm birth and large for gestational age were similar in subgroups of women with various baseline characteristics. Adjusted risk ratio for preterm birth per standard deviation fasting glucose (0.7 mmol/L) was 0.99 (95% confidence interval, 0.98-1.00), for early preterm birth an adjusted risk ratio of 0.99 (confidence interval, 0.97-1.02), for large for gestational age an adjusted risk ratio of 1.04 (confidence interval, 1.03-1.05), and for severe large for gestational age an adjusted risk ratio of 1.03 (confidence interval, 1.01-1.04). Our data suggest that maternal prepregnancy impaired fasting glucose increases the risk of preterm birth, large for gestational age, and severe large for gestational age. Data also suggest that the World Health Organization cut point of impaired fasting glucose is too restrictive, and lower levels of fasting glucose also increase the risk of large for gestational age and severe for severe gestational age in the Chinese population. Further investigation is warranted to determine whether and how counseling and interventions for women with prepregnancy impaired fasting glucose could reduce the risk of preterm birth and large for gestational age.