Objective: The aim of the study was to determine normative values of intracranial translucency (IT) by ultrasonography in singleton pregnant women patient at Thammasat University Hospital during the first trimester.
Material and Method: The first trimester singleton pregnant women (11-13 weeks) underwent routine ultrasonography
screening. The gestational age was calculated by measuring the length of the embryo or fetus from the top of its head to bottom of the buttocks (crown-rump length; CRL) and IT of the brain region in the mid-sagittal planefetal face position. Repeated ultrasonography was performed in the second trimester period as well as after birth infant check-up for disability.
Results: One hundred and ninety one singleton pregnant women were examined by an ultrasonography to measure CRL, GA and IT. The average age was 29.71+5.09 years (16-39 years). All participants were healthy without a history of anomaly in previous pregnancies. Half of cases were nulliparity. Participants were followed until birth. There was no open neural tube defect baby in this study. Median GA, CRL and IT in this study were 12.6+0.7 weeks, 64.0+10.2 (40.0-80.9) and 1.3+0.3 (0.5-2.5) mm, respectively. IT measurement value increased in correlation with increasing CRL and advancing GA (p<0.05).
Conclusion: IT values increased significantly with CRL and GA increasing.

Keywords: First trimester, Intracranial translucency, Ultrasound