Foetal sex determination at the second trimester anomaly scan in Denmark

For decades, ultrasound has enabled determination of foetal sex. Foetal sex is medically indicated in sex-linked diseases, syndromes and multiple pregnancy, but genital malformations are rare. However, guidelines on standard views seem sparse and foetal sex determination is not considered mandatory. The aim of this study was to provide an initial overview on the practice of foetal sex determination in Denmark and the accuracy of the examinations at the second trimester anomaly scan at a regional and a university hospital.

Phone interviews from all 23 Danish foetal medicine departments concerning information, examination, registration, quality criteria and assessment of accuracy. The accuracy of foetal sex determination was assessed in 5,786 singleton pregnancies with live births at two departments by comparison of data from the second trimester anomaly scan (week 18 + 0 - 21 + 6) with the national Danish birth register.

Second trimester foetal sex determination was not mandatory but conducted without guideline. Various approaches to information and documentation were used. Foetal sex was assessed in 86.7% of cases and the accuracy was 99.2% with no significant difference between the regional and the university hospital of the study. Sex determination was more inaccurate in females (18/2,118) than in males (18/2,271), p < 0.0001.

Foetal sex determination by ultrasound is common practice in Denmark. No guideline existed and incorrect sex was determined in 8/1,000 foetuses, most often females. Foetal sex determination should be standardised extensively to avoid false diagnoses.

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This study was approved by the Danish Data Protection Agency (record number: 2012-41-0050).