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

Abstract

Background The impact of maternal pre-pregnancy impaired fasting glucose on preterm birth and large for gestational age has been poorly understood.

Objectives We aimed to estimate the impact of pre-pregnancy impaired fasting glucose defined by the WHO cut-point on the risk of preterm birth and large for gestational age, and to investigate whether the WHO cut-point of impaired fasting glucose was appropriate for identifying women at the risk of preterm birth and large for gestational age among the Chinese population.

Study Design 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 1st January 2013 to 31st December 2017. Women were included if pre-pregnancy fasting glucose was less than 7.0mmol/L. The primary outcomes were preterm birth (gestational age <37 weeks), early preterm birth (gestational age <34 weeks), large for gestational age (birth weight by gestational age >90th percentile based on the international standards in the INTERGROWTH-21st) and severe large for gestational age (birth weight by gestational age >97th percentile). We calculated the adjusted risk ratio for impaired fasting glucose, and a 1 standard deviation increase in fasting glucose.

Results We included 640469 women. Of these, 31006 (4.84%) met the WHO cut-point for impaired fasting glucose, 32640 (5.10%) had preterm birth and 7201 (1.12%) had early preterm birth, 45532 (7.11%) had large for gestational age birth and 16231 (2.53%) had severe large for gestational age birth. Compared with women with normoglycaemia, women with pre-pregnancy impaired fasting glucose had a 7.0% higher risk of preterm birth (adjusted risk ratio 1.07, 95%CI 1.02-1.12), 10.0% higher risk of large for gestational age (1.10, 1.06-1.14) and 17.0% higher risk of severe large for gestational age (1.17, 1.10-1.26). No significant association of pre-pregnancy impaired fasting glucose with early preterm birth was found. The association of pre-pregnancy 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 (0.7mmol/L) was 0.99 (95% CI 0.98-1.00), for early preterm birth 0.99 (0.97-1.02), for large for gestational age 1.04 (1.03-1.05) and for severe large for gestational age 1.03 (1.01-1.04).

Conclusions Our data suggest that maternal pre-pregnancy impaired fasting glucose increases the risk of preterm birth, large for gestational age and severe large for gestational age. Data also suggest that the WHO cut-point of impaired fasting glucose is too restrictive and lesser levels of fasting glucose also increase the risk of large gestational age and severe for severe gestational age in the Chinese population. Further investigation is warranted to determine whether and how counselling and interventions for women with pre-pregnancy impaired fasting glucose could reduce the risk of preterm birth and large for gestational age.