Objective: To evaluate levels of 24-hour urine insulin excretion before the onset of pre-eclampsia and gestational hypertension.
Design: Nested case-control study within the Calcium for Preeclampsia Prevention (CPEP) study cohort.
Setting: Five university medical centres in the United States.
Sample: Cases had developed pre-eclampsia (n= 70) or gestational hypertension (n= 142) in the absence of gestational diabetes. Controls (n= 429) had remained normotensive without gestational diabetes.
Methods: Subjects were required to have had an adequate baseline 24-hour urine collection prior to CPEP enrolment at 13-21 weeks. Controls were matched to cases by enrolment site and specimen storage time, without regard to gestational age or CPEP treatment. Adjusted mean 24-hour urine insulin excretion was, however, calculated using analysis of covariance, with adjustment models for pre-eclampsia considering body mass index, race and smoking status; and for gestational hypertension, gestational age at specimen collection, height, body mass index and smoking. Urine insulin was measured by radio-immunoassay.
Main outcome measures: Twenty-four-hour urine insulin excretion.
Results: Adjusted 24-hour urine insulin excretion at baseline (mean 17 weeks of gestation) was greater in women who developed pre-eclampsia than in normotensive controls (mean [SE]: 15.6 [1.5] vs 13.1 [1.2] x 10(3)microIU/24 hour, P= 0.06), but not in women who developed gestational hypertension (14.7 [0.9] vs 15.0 [0.6] x 10(3)microIU/24 hour, P= 0.79, in cases vs controls). Among women who developed pre-eclampsia, adjusted urine insulin excretion was greater than controls only in women with mild pre-eclampsia and not in severe pre-eclampsia (mild pre-eclampsia vs controls: 17.3 [2.0] vs 13.7 [1.6] x 10(3)microIU/24 hour, P= 0.04; severe pre-eclampsia vs controls: 12.3 [2.2] vs 11.5 [1.2], P= 0.69).
Conclusion: The data suggest that early hyperinsulinaemia, a marker of insulin resistance, may predispose to mild pre-eclampsia.