Nomogram of nuchal fold thickness of Thai fetuses.

The aim of the study was to establish normal values of nuchal fold thickness during 14-21 weeks of pregnancy. Three hundred Thai pregnant women before 12 weeks of gestation were recruited. Gestational age was determined by last menstrual period and confirmed by crown-rump length. Subjects with date-size discrepancy of more than 7 days were excluded from the study. Nuchal fold thickness was measured twice, first during 14-17 weeks, and then during 18-21 weeks. Five hundred and nine measurements were obtained. Nomogram of nuchal fold thickness was constructed. Mean values of nuchal fold thickness increased steadily from 2.59 +/- 0.77 millimeters (mm) at 14 weeks to 4.12 +/- 0.98 mm at 21 weeks. Average rate of increase were 0.22 mm per week. In conclusion, nuchal fold thickness increased with advancing gestational age from 14 to 21 weeks of pregnancy. Different normal cut-off levels for each gestational week may be more appropriate for screening of fetal Down syndrome in Thai pregnant women.