OBJECTIVE: Aim of the study was to assess the percentage and type of anomalies (structural and chromosomal) that can be detected at an early scan performed at 12-13 weeks' gestation, as opposed to the present screening policy (20 -week scan). METHODS: Sonographers accredited for the nuchal translucency (NT) measurement were asked, after additional training, to participate into the study. The early scans were performed according to a protocol, in six ultrasound practices and 2 referral centers in the Northeast of the Netherlands. All women opting for the combined test (CT) or eligible for a scan at a referral center in view of an increased a-priori risk of fetal anomalies were offered a scan at 12-13 weeks' gestation (study group). RESULTS: The study group consisted of 5,237 women opting for the combined test (CT) and 297 women with an increased a-priori risk of anomalies (total 5,534). In the study population in total 53 structural and 34 chromosomal anomalies were detected prenatally and 18 more structural anomalies were detected after birth. Overall 87 anomalies (63%) where detected at the early scan (24/53 (45.3%) structural and all the ultrasound detectable chromosomal anomalies, some in view of structural anomalies). Especially severe anomalies were detected at the early scan (all cases of neural tube defect, omphalocele, megacystis, multiple severe congenital and severe skeletal anomalies). The NT was increased in 12/24 (50%) anomalies detected at the early scan. Of the 12 heart defects, 4 (33,3%) were detected at the early scan, 5 (41,7%) at 20 weeks and 3 (25%) after birth. False positive diagnoses at the early scan and at the 20 weeks scan occurred in 0.09% and 0.6%, respectively, whereas ultrasound markers in 1.4% and 3%, respectively. After first or second trimester diagnosis, parents elected to terminate the pregnancy (TOP) in 54% and 24% of cases, respectively. CONCLUSION: An early scan (12-13 weeks) performed by competent sonographers can detect about half of the prenatally detectable structural ...