Natural evolution of nuchal thickness in trisomy-21 fetuses

Objective: To assess the natural evolution of nuchal thickness in trisomy-21 fetuses. Methods: Serial measurements of nuchal thickness were performed over a 1- to 6-week period in 45 consecutive fetuses with trisomy 21, between the 10th and the 23rd weeks of pregnancy. To avoid a gestational age confounding effect, nuchal thickness also was expressed in standard deviations (SDs) for the corresponding gestational week. In addition, the changes were assessed in terms of the presence of clinical positive thickening, considered as such when the measurement was above 2.5 SD. Results: A mean increase of 1.8 mm (95% confidence interval [CI] 1.3, 2.3) for nuchal thickness was observed for a mean period of 21 days. When corrected by gestational age, the mean increase of 0.3 SD (95% CI -0.2, 0.9) was found to be not significant. No clinically relevant nuchal thickening changes were recorded (51% versus 69%) at re-examination. Conclusion: Nuchal thickening at re-examination is observed in a similar proportion of trisomy-21 fetuses as when first observed. (C) 1998 by The American College of Obstetricians and Gynecologists.