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.