First‐trimester cavum veli interpositi: prevalence and natural history

ABSTRACT Objective To confirm the identity and assess the prevalence and evolution of the fluid‐filled interhemispheric midline structure, thought to be the cavum veli interpositi (CVI), in fetuses at 11–14 weeks' gestation. Methods This was a retrospective study of first‐trimester ultrasound scans performed at a single center over 3 months. Inclusion criteria were singleton pregnancies at 11–14 weeks' gestation with known neonatal outcome. Five experts reviewed the images. Mixed‐effects logistic regression and generalized estimating equations (GEE) were conducted to analyze the associations between the presence of the structure and variables including ultrasound approach (transabdominal vs transvaginal), maternal body mass index (BMI), gestational age, fetal crown–rump length (CRL) and biparietal diameter (BPD). Second‐trimester ultrasound scans of the fetal central nervous system at 18–24 weeks' gestation were evaluated for the persistence of the CVI in fetuses in which the structure was observed in the first trimester. Results Of the 223 cases reviewed, 104 were included, among which the CVI was observed in 25 (24%) cases. There was no statistically significant difference in CVI visualization between transabdominal and transvaginal ultrasound examinations. GEE showed significant associations between the presence of the fetal structure and CRL (odds ratio (OR) per 10‐unit increase, 1.32; P