Sonographic Evaluation of Fetal Growth in the Third Trimester of Low-risk Pregnancy: a Randomized Trial

Sonographic fetal weight estimation at the last weeks of third trimester in low-risk pregnancies is an effective method for diagnosis of fetal growth restriction (FGR) permitting close surveillance and timely delivery. The need for a systematic ultrasound evaluation at the last weeks of a low-risk pregnancy and the best time to perform it remains controversial. The most commonly used clinical screening tool in this population is the serial measurement of symphysis-fundus distance, which is a method of a variable and low sensitivity for detection of FGR. In Portugal, in accordance with guidelines of Direcção Geral de Saúde from 2015, fetal growth restriction screening in low risk pregnancies is performed with an ultrasound for fetal weight estimation at 30th-33rd weeks. Nonetheless, recent data from randomized trials showed that FGR detection rate was superior at 36 vs 32 weeks' gestation. In cases of severe FGR, detection rate was also superior at 36 vs 32 weeks' gestation. In a prior retrospective study, our group analyzed 1429 term low risk pregnancies and the investigators concluded that small for gestational age term babies (birthweight \< 10th centile) had a statistically significant higher rate of operative deliveries for intrapartum fetal distress than appropriate for gestational age as well as a higher rate of admission to neonatal intensive care unit. Moreover the investigators compared the same outcomes within small for gestational age neonates with antepartum detection at 30th-33rd weeks ultrasound vs undetected (normal 30th-33rd weeks ultrasound). Antepartum detection of small for gestational age neonates showed a statistically significant lower rate of operative deliveries for intrapartum fetal distress than undetected small for gestational age neonates. The investigators will conduct a prospective randomized clinical trial with the aim to evaluate if a 35th-37th weeks after the standard of care ultrasound in low risk pregnancies is effective in improv