Implications and Outcomes of Fetal Dilated Fourth Ventricle in the First Trimester

Many pregnant patients now undergo non-invasive prenatal testing (NIPT) from 10 weeks of gestation to screen for fetal aneuploidy (common trisomies – trisomy 21, trisomy 18 and trisomy 13). In general, an ultrasound examination to ensure fetal viability and confirm gestational age is recommended prior to NIPT, which is giving us the opportunity to assess very early fetal anatomy in a large number of patients. We have recently observed that a dilated fourth cerebral ventricle at 10-14 weeks seems to be associated with underlying chromosomal anomalies, in particular triploidy. Using data on routine ultrasound examinations from Monash Ultrasound for Women (MUFW), we aim to review the investigations and outcomes of fetuses with dilated fourth ventricle, in particular the rate of associated structural abnormalities and underlying chromosomal or genetic syndromes.