Assessment of Foetal Nuchal Translucency and its Relationship with Crown Rump Length in Normal Foetuses using Ultrasonography in a Subset of South Indian Population

Introduction: Assessing Nuchal Translucency (NT) accurately is necessary in detection of various anomalies as described in the literature. Studies deriving reference range for NT in Indian population is not widely available.

Aim: To derive a normal reference range value of NT with respect to Crown Rump Length (CRL) by using ultrasound in South Indian population.

Materials and Methods: A cross-sectional study was conducted on 470 pregnant women from December 2018 to March 2020. Measurement of NT thickness and CRL was performed by ultrasound at 11-14 weeks of gestation. Association between quantitative explanatory and outcome variables was assessed by calculating Pearson correlation coefficient and the data was represented in a scatter diagram. The relationship between NT thickness, CRL and gestational age was studied by using linear regression analysis. The Statistical Package for Social Sciences (SPSS) software version 22.0 was used for statistical analysis. The p-value less than 0.05 was considered statistically significant.

Results: Total sample of 470 pregnant females (mean age 25.626±3.82 years, 357 multipara, mean gestational age 12.60±1.36 weeks) was analysed. The mean CRL was 59.84±10.17 mm and mean NT thickness was 1.3±0.26 mm, respectively. The median gestational age was 12.4 weeks. The regression equation which showed relation between median NT thickness and CRL was described as follows: Expected NT thickness=-1.652+(0.050)×CRL mm (R2 linear=0.995, p<0.0001).

Conclusion: The study provides normative data of NT thickness in normal foetus. This data can be used as reference to screen various chromosomal abnormalities between 11-14 weeks of gestation.