Association between maternal serum analytes and third trimester fetal growth restriction.

Background: Given associations between abnormal maternal serum analytes and small for gestational age, 3^rd trimester fetal growth ultrasounds are commonly obtained despite lack of evidence. We evaluated associations between isolated abnormal analytes, 3^rd trimester fetal growth restriction, and neonatal complications.

Methods: This retrospective, single institution cohort study included women with analytes from 2010-2019. Multiple gestation, delivery <28 weeks gestation, and those with another indication for a 3^rd trimester US were excluded. Fetal growth restriction prevalence at the first 3^rd trimester US with abnormal analytes was calculated, as well as its association with small for gestational age. Associations between abnormal analytes and neonatal outcomes (small for gestational age, intensive care, umbilical artery pH <7.0, 5-minute APGAR <7, preterm delivery, neonatal death) were also evaluated.

Results: Among 11,092 pregnancies, 1136 had isolated abnormal analytes, of which 613 had 3^rd trimester ultrasounds. Of these, 10 (1.6%) had growth restriction at the first 3^rd trimester ultrasound, and 99 (16.1%) were small for gestation. Abnormal analytes were associated with increased small for gestational age, intensive care admit, and preterm delivery. Only 9.1% of small for gestational age neonates had growth restriction at the first 3^rd trimester ultrasound.

Conclusions: Third trimester fetal growth restriction is uncommon with isolated abnormal analytes, and early 3^rd trimester ultrasound for this indication may commonly miss small for gestational age. These findings contribute to 1) evidence-based fetal surveillance in this setting, and 2) knowledge regarding potential implications on growth restriction detection by replacing serum analyte screening with cell free fetal DNA.