Is There a Threshold Oral Glucose Tolerance Test Value for Predicting Adverse Pregnancy Outcome?

Abstract

Objective: This study aims to determine whether there is a threshold 3-hour oral glucose tolerance test (OGTT) value associated with accelerated risk of adverse pregnancy outcomes.

Study design: In a secondary analysis of a cohort of women with untreated mild gestational glucose intolerance, we used generalized additive models with smoothing splines to explore nonlinear associations between each of the 3-hour OGTT values (fasting, 1-hour, 2-hour, and 3-hour) and adverse pregnancy outcomes, including the study's composite outcome (perinatal mortality, hypoglycemia, hyperbilirubinemia, neonatal hyperinsulinemia, and/or birth trauma), large for gestational age birth weight, small for gestational age birth weight, shoulder dystocia, neonatal hypoglycemia, gestational hypertension (gHTN), and preeclampsia.

Results: Among the 1,360 eligible women, each timed OGTT value was linearly associated with increased odds of composite adverse outcome. We found evidence of a departure from linearity only for the association between fasting glucose and gHTN/preeclampsia, with a stronger association for values of 85 to 94 mg/dL (p = 0.03). We found no evidence of departure from linearity for any other OGTT values and measured outcomes (all chi-square test p-values ≥ 0.05).

Conclusion: In a population of untreated women with mild gestational glucose intolerance and fasting OGTT < 95 mg/dL, we found an increasing risk of gHTN with a fasting glucose between 85 and 94 mg/dL.

Figure

Non-parametric associations between OGTT values and pregnancy outcomes. The black line indicates the predicted probability of an outcome, and the grey region indicates the 95% confidence interval around that predicted probability. We found a statistically significant departure from linearity for fasting glucose and gestational hypertension/preeclampsia (top left), with an increase in the slope of the association for glucose values between 85 and 94 mg/dL (top left). We found linear associations between 3-hour OGTT parameters and gestational hypertension/preeclampsia (1-, 2- and 3-hour ), the primary outcome (all OGTT parameters), LGA (fasting, 1- and 2-hour), and shoulder dystocia (1- and 2-hour).