Value of routine ultrasound examination at 35-37 weeks' gestation in diagnosis of fetal abnormalities

Objective: To investigate the potential value of routine ultrasound examination at 35-37 weeks’ gestation in the diagnosis of previously unknown fetal abnormalities.

Methods: This was a prospective study in 52,401 singleton pregnancies attending for a routine ultrasound examination at 35+0 - 36+6 weeks’ gestation; all pregnancies had a previous scan at 18-24 weeks and 47,215 also had a scan at 11-13 weeks. We included pregnancies resulting in livebirth or stillbirth but excluded those with known chromosomal abnormalities. The abnormalities were classified according to affected major organ system and the type and incidence of new abnormalities was determined.

Results: In the study population the incidence of fetal abnormalities was 2.2% (1,168 / 52,401), including 847 (72.5%) that had been previously diagnosed during the first and / or second trimester, 247 (21.2%) that were detected for the first time at 35-37 weeks and 74 (6.3%) that were detected for the first time postnatally. The most common abnormalities that were diagnosed during the first and / or second trimester, that were also observed at 35-37 weeks, included aberrant right subclavian artery, ventricular septal defect, talipes, unilateral renal agenesis and / or pelvic kidney, hydronephrosis, duplex kidney or unilateral multicystic kidney, cystic pulmonary airway malformation, ventriculomegaly, cleft lip and palate, polydactyly,abdominal cyst or gastroschisis. The most common abnormalities seen at 35-37 weeks were hydronephrosis, mild ventriculomegaly, ventricular septal defect, duplex kidney, ovarian cyst and arachnoid cyst. The incidence of abnormalities first seen at 35-37 weeks was 0.5% and the most common were ovarian cysts, microcephaly, achondroplasia, dacryocystocele and hematocolpos. The incidence of abnormalities first seen postnatally was 0.1% and the most common were isolated cleft palate, polydactyly or syndactyly and ambiguous genitalia or hypospadias; prenatal examination of the genitalia was not a compulsory part of the protocol.

Conclusions: A high proportion of fetal abnormalities are detected for the first time during a routine ultrasound examination at 35-37 weeks’ gestation. Such diagnosis and subsequent management, including selection of time and place for delivery and postnatal investigations, could potentially improve postnatal outcome.

Fetal Medicine Foundation Grant Number: Charity No: 1037116