Impact of new definitions of pre-eclampsia on incidence and performance of first-trimester screening

Objective: The traditional definition of pre-eclampsia (PE) is based on the development of hypertension and proteinuria. This has been revised recently to include cases without proteinuria but with evidence of renal, hepatic or hematological dysfunction. The aim of this study was to examine the impact of new definitions of PE on, first, the incidence and severity of the disease and, second, the performance of the competing-risks model for first-trimester assessment of risk for PE.

Methods: This was a retrospective study of 66 964 singleton pregnancies that were classified as having PE, gestational hypertension (GH) or no PE or GH, according to the traditional criteria of the International Society for the Study of Hypertension in Pregnancy (ISSHP-old), which defines PE as the presence of both hypertension and proteinuria. We reviewed the records of pregnancies with GH, and those cases with high creatinine or liver enzymes or low platelet count were reclassified as having PE, according to the new criteria of ISSHP (ISSHP-new) and the new criteria of the American College of Obstetricians and Gynecologists (ACOG). The groups of PE according to the traditional and new criteria were compared for, first, gestational age at delivery, birth-weight percentile and incidence of a small-for-gestational-age (SGA) neonate with birth weight < 10th percentile and perinatal death, and, second, the predictive performance for preterm PE of the competing-risks model based on the combination of maternal risk factors, uterine artery pulsatility index, mean arterial pressure and serum placental growth factor at 11-13 weeks' gestation (triple test).

Results: According to ISSHP-old, 1870 (2.8%) cases had PE, 2182 (3.3%) had GH and 62 912 (94.0%) had no PE or GH. The incidence of PE according to ACOG was 3.0% (2029/66 964) and ISSHP-new was 3.4% (2301/66 964). Median gestational age at delivery in the extra cases of PE according to ACOG (difference, 1.3 weeks; 95% CI, 0.71-1.71 weeks) and in the extra cases of PE according to ISSHP-new (difference, 1.5 weeks; 95% CI, 1.29-1.71 weeks) was higher than in cases with PE according to ISSHP-old (38.4 weeks). The incidence of a SGA neonate in the extra cases of PE according to ACOG (relative risk, 0.57; 95% CI, 0.42-0.79) and in the extra cases of PE according to ISSHP-new (relative risk, 0.52; 95% CI, 0.42-0.65) was lower than in the cases of PE according to ISSHP-old (33.64%). In first-trimester screening for preterm PE by the triple test, the detection rate, at a 10% false-positive rate, was 75.9% (95% CI, 70.8-80.6%) for ISSHP-old, 74.3% (95% CI, 69.2-79.0%) for ACOG and 74.0% (95% CI, 68.9-78.6%) for ISSHP-new.

Conclusions: The new definitions of PE resulted in, first, an increase in pregnancies classified as having PE but the additional cases had milder disease, and, second, a non-significant decrease in the performance of first-trimester screening for PE.