Prediction model for hypertension in pregnancy in nulliparous women using information obtained at the first antenatal visit.

OBJECTIVE: To develop a prediction model for the occurrence of hypertension in pregnancy using clinical variables obtained routinely at the antenatal booking visit prior to 16 weeks gestation.
METHODS: We studied 2334 nulliparous pregnant women participating in two population-based prospective cohort studies. Potential predictors included maternal age, blood pressure, body weight, height, previous miscarriage and smoking history, assessed at the visit booking prior to 16 weeks gestation. The outcome measure was the development of hypertension before 36 weeks of gestation. A prediction model was derived from the regression model using discrimination, calibration, bootstrapping approaches and transformed into a prediction model usable in clinical practice.
RESULTS: One hundred and forty-one of 2334 women (6.0%) developed hypertension. Main predictors were systolic and diastolic blood pressure, and weight. The area under the receiver operating characteristic curve of the model was 0.78, 95% confidence interval (CI) 0.75-0.82. Among women with a very low score (19% of the population) the risk of hypertension was 0.5%. In those with a high score (13% of the population) the risk was 22.9%.
CONCLUSION: Among nulliparous and initially normotensive women, the use of three simple clinical variables obtained routinely at the antenatal booking visit prior to 16 weeks, can accurately identify women at very low and very high risk of becoming hypertensive before 36 weeks of gestation. When confirmed in recent cohorts, application of the prediction model may lead to a reduction in frequency of antenatal visits for low-risk and increased surveillance for high-risk women.