138: Congenital malformations detected during routine third-trimester growth scan: a population-based study

Abstract

Routine third-trimester fetal growth scans are increasingly recommended. Our aim was to evaluate the number and nature of congenital malformations detected in the third trimester in women attending a universal late growth scan. Population-based study of women receiving care in Oxfordshire, UK over 2 years. Eligible women had a viable singleton pregnancy and an estimated due date between October 2016 and September 2018. Standard care included sonographer performed and reported nuchal translucency scan at 11-13 weeks, combined biochemical testing, an anomaly scan at 19-21 weeks, and a growth scan at 35-37 weeks. The fetal growth scan consisted of biometry, amniotic fluid volume, and Doppler measurements, but not formal reassessment of anatomy. Suspected fetal malformations were referred for fetal medicine evaluation. Prenatal ultrasound data and postnatal diagnoses were collected for all pregnancies. We assessed the rate and timing of prenatal detection of fetal congenital malformations in the cohort. There were 15,244 women attending routine antenatal care. Malformations were detected prenatally in 332: 104 (31%) were detected before the anomaly scan, 176 (53%) at the anomaly scan, 9 (3%) after but before the third-trimester scan, and 43 (13%) at the third-trimester scan (Table). In a further 150 neonates, an anomaly was detected postnatally. Of major malformations, 68% were detected before the third-trimester growth scan, 3% at the third-trimester growth scan, and 29% after birth. The malformations detected at the routine third-trimester growth scan were most commonly urinary tract dilatation, ventriculomegaly, and abdominal cysts. Of the third-trimester malformations, 33 (77%) were confirmed postnatally; 21 (49%) were minor renal abnormalities, 2 (5%) were chromosomal and none were cardiac. A universal third-trimester growth scan in a previously screened population will incidentally identify a congenital malformation in about 1 in 350 pregnancies, however, detection rates of major malformations are affected very little.