Ultrasound detection of placental insufficiency in women with elevated second trimester serum alpha-fetoprotein or human chorionic gonadotropin

Abstract

Objective: We evaluated the role of placental morphology ultrasound and uterine artery Doppler in predicting adverse perinatal outcomes in women with unexplained elevated serum alpha-fetoprotein (AFP) or human chorionic gonadotropin (hCG) levels in the second trimester of pregnancy.

Methods: Women with a serum AFP > 2.0 MoM (n = 83) or serum hCG > 2.5 MoM (n = 68) had placental imaging at 19-23 weeks' gestation. Abnormal placental morphology (i.e., a maximum thickness of > 4 cm or > 50% of length) and abnormal uterine artery Doppler [UTAD] (mean pulsatility index > 1.45) were related to placental complications of pregnancy. Relative risks were derived for all women. Likelihood ratios were derived for the subset (55/83) in the group with elevated AFP who had no medical and/or obstetrical risk factors.

Results: Compared with elevated serumh CG, an elevated serum AFP was associated with higher rates of perinatal mortality (15.6% vs. 4.3%), preterm birth at < 32 weeks' gestation (26.5% vs. 7.3%), small-for-gestational age (SGA) birth weight < 10th centile (24.1% vs. 10.3%) and severe intrauterine growth restriction (IUGR) (8.4% vs. 2.8%). Thirty-seven (44.5%) women with elevated serum AFP had an adverse perinatal outcome, and 23 of these women (67%) had no prior medical and/or obstetric risk factors. Abnormal tests of placental function were more common in the elevated serum AFP group than in the hCG group (UTAD 30.1% vs. 11.6%; placental morphology 30.2% vs. 16.2%). Abnormal UTAD and abnormal placental morphology had similar positive likelihood ratios for a range of adverse perinatal events in the elevated AFP group (1.3-4.4) and were increased when both tests were abnormal (likelihood ratio 5.0 for preeclampsia, 4.5 for preterm delivery < 32 weeks, 4.9 for intrauterine fetal demise). In the elevated hCG group abnormal UTAD and abnormal placental morphology predicted SGA (likelihood ratios 5.2 and 4.9) and IUGR (likelihood ratios 4.7 and 7.3) but did not predict preeclampsia or preterm birth.

Conclusion: Assessment of placental function using either morphology or UTAD at 19-23 weeks' gestation identifies a subset of women at increased risk of adverse perinatal events with an elevated serum AFP. These tests have more limited value in women with an elevated serum hCG because of the lower prevalence of adverse perinatal events.