The nomogram of intracranial translucency in the first trimester in singletons

Measurement of intracranial translucency (IT), which is a recent earlier recognizable sonographic marker, has been suggested for detection of spina bifida. In this prospective study we aimed to determine normative values of IT in the population of Turkish singleton pregnant women during the first trimester of pregnancy.

Between January 2011 and July 2011, all consecutive singleton pregnant women were screened for intracranial translucency. Pregnancies were followed until birth. Pregnancies with any detected/suspicious anatomical or genetic fetal anomalies, biochemical abnormalities, increased nuchal translucency measurements, pregnancies of artificial reproduction techniques and anomaly detected at birth were set to be excluded from the data analyses. Mean±standard deviation, median and percentile values of intracranial translucency were calculated. Linear regression analyses were done between the length of intracranial translucency and gestational week and CRL.

Data analyses included 201 fetuses. Median maternal age was 31 years. Median CRL was 62 mm. Median gestational week was 12.57 weeks. Median IT value for the first trimester was 1.7 mm (range 1.00-2.40). Calculated formulae are; IT (mm)=[0.237×Gestational Week)]-1.27, R(2)=0.302; p<0.001 and IT (mm)=[0.020×CRL (mm)]+0.44, R(2)=0.381; p<0.001). IT measurements increased with increasing CRL and advancing gestational weeks. During follow up none of the fetuses was found to have any anatomical abnormality or anomaly.

This study presents normative values of intracranial translucency in the first trimester screening of normal singleton pregnancies of the Turkish population. In accordance with previous reports, intracranial translucency increases linearly with advancing CRL.