Statistical analysis
Categorical variables were expressed as absolute numbers and percentages, and continues variables were expressed in medians and interquartile ranges (IQR). Differences in characteristics between the study groups were examined with chi-square or Fisher’s exact test in case of categorical variables, and t test or Mann-Whitney U test for continuous variables depending on the distribution. The agreement between the two operators regarding classification of the type of oedema was assessed with analysis of intraclass correlation coefficient (ICC).
The primary outcome of the study was the occurrence of chromosomal abnormalities. Pregnancy outcomes, karyotype and microarray abnormalities and ultrasound findings associated with early fetal oedema are described as proportions within each group.
Finally, the association between oedema thickness with CRL 28 - 44 mm and the nuchal translucency at 11 to 13+6 weeks was assessed through linear regression analysis, and rates and outcomes of persistently increased nuchal translucency above the 99th percentile (3.5 mm) were reported. For this purpose, adverse outcomes were defined as at least one of miscarriage, termination of pregnancy, relevant chromosomal abnormality or major structural defects.
A two-tailed 0.05 significance level was adopted, and statistical analyses were performed in SPSS version 25.0® (IBM Corp. Released 2017. IBM SPSS Statistics for Macintosh, Version 25.0. Armonk, NY: IBM Corp.).