Increased nuchal translucency at a crown rump length < 45 mm

Aim: Nuchal translucency (NT) measurement is established for risk evaluation of chromosomal abnormalities between a crown rump length (CRL) of 45 to 84 mm. According to the german regulations the first ultrasound screening takes place between 9th and 11th week of gestation. This results in cases with increased NT and CRL < 45 mm, where risk calculation is impossible. In this retrospective study we analysed the outcome of these cases.

Methods: Between July 2010 and September 2015 we identified 24 pregnancies with a CRL from 35 to 45 mm and a NT above the 95th centile adjusted for a CRL equivalent of 45 mm. Measurement of CRL and NT was performed by four FMF London certified examiners. The outcome was evaluated by data base analysis and direct contact to the patient.

Results: Median CRL was 43 mm (35.4 – 44.9 mm) with a median NT of 3.9 mm (2.5 – 6.6. mm). Median maternal age was 29 years (14 – 38 years). In 17 of 24 cases (71%) the pregnancy resulted in a delivery of a healthy child. In one of these cases a minor ventricular septal defect was diagnosed postnatally. In 16 of 24 cases (67%) an invasive procedure was performed for fetal karyotyping revealing six fetuses (25%) with chromosomal disorders resulting in the termination of pregnancy. In one case with normal karyotype further sonograms revealed a complex sydrome with hypoplastic cerebellum. In all cases without karyotyping outcome was normal at delivery. The NT in all cases with abnormal karyotype was ≥3.9 mm.

Discussion: In cases with NT < 3.9 mm and CRL ≤45 mm it is very likely, that a healthy child will be born. Lacking the possibility of risk calculation non-invasive prenatal testing (NIPT) may be the first choice for these pregnancies.