Incidence of gestational diabetes in pregnant women with a history of bariatric surgery using a service evaluation.

Background: Pregnant women with previous bariatric surgery are at increased risk of gestational diabetes mellitus (GDM) but many cannot safely tolerate the oral glucose tolerance test (OGTT). Consensus recommendations advise self-monitoring of blood glucose (SMBG) for GDM diagnosis, but diagnostic thresholds are unexplored in this population.

Study objective: To assess the incidence of SMBG-defined GDM (fasting, 1-hr postprandial thresholds: 90, 140 mg/dL (5.3, 7.8 mmol/L)) after bariatric surgery, compared to the incidence of OGTT-defined GDM in women with risk factors for GDM but no history of bariatric surgery.

Design and setting: Patients with a history of bariatric surgery (n=24) were included in a retrospective service evaluation based at a single tertiary referral centre in England, with results compared to a national study of women at high risk of GDM but without a history of bariatric surgery (n=1,308).

Main outcome measures: The incidence of GDM diagnosed according to SMBG vs OGTT.

Results: GDM incidence was 16/24 (66.7%; SMBG-defined) after bariatric surgery and 121/1,308 (9.3%; OGTT-defined) in the control group, with the highest incidence rates seen after gastric bypass (85.7%). In women with previous bariatric surgery, HbA1c showed no association with GDM diagnosis, the requirement for treatment or offspring birth weight.

Conclusions: SMBG at standard thresholds is not able to reliably diagnose GDM after bariatric surgery and is likely to over-diagnose GDM, especially after gastric bypass, although small sample size limits generalisability of this study. Alternative diagnostic and prognostic markers are warranted for diagnosis of GDM after bariatric surgery.