Objective: Gestational diabetes (GDM) incidence reportedly demonstrates seasonal variation. We aimed to assess if season also affects maternal-fetal outcomes in GDM.

Methods: 23,735 women who consecutively delivered singleton, live-born, term infants in a tertiary obstetrics center (2004-08; 4.6% GDM) were included. Additive dynamic regression models (age, BMI, parity, ethnicity adjusted) compared GDM incidence and outcomes (GDM diagnosis, birth weight, delivery mode) over annual cycles.

Results: GDM incidence varied by 30% from peak (October births) to nadir (March births; p<0.05). Temperature at time of test (28 weeks) was strongly positively associated with diagnosis (p<0.001). Birth weight in GDM-affected pregnancies showed marked seasonal variation (mean: 58th centile June - Sept; 67th centile Dec-Mar; p<0.05; fig). Emergency Caesarean rates (50% variation, p<0.05), closely temporally correlated with birth weight.

Conclusions: Substantial seasonal variation exists in GDM diagnoses and maternal-fetal outcomes in GDM-affected pregnancies. Birth weight is highest when GDM diagnoses are lowest, implying either over-diagnosis in summer or more challenging glycemic control in winter. Considering seasonal variation gives new opportunities for intensive individualized therapy to improve outcomes.

Figure: Effect of season on birthweight centiles in GDM; p<0.05.
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Disclosure

C.L. Meek: None. B.O. Devoy: None. D. Simmons: Speaker's Bureau; Self; Sanofi-Aventis. Other Relationship; Self; Medtronic. C. Patient: None. H.R. Murphy: Advisory Panel; Self; Medtronic MiniMed, Inc. C. Aiken: None.

Funding

Diabetes UK (17/0005712 to C.L.M.)

© 2019 by the American Diabetes Association.
2019
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