Early second‐trimester determination of fetal gender by ultrasound

Abstract

Ultrasound identification assists in determining chorionicity in twins, in the interpretation of sex chromosome mosaicism and aneuploidy and in sex-linked conditions presenting after 14 weeks. This study addresses the frequency and accuracy of gender identification in a series of consecutive patients presenting for amniocentesis for genetic indications. Amniocentesis was performed at 14-20 weeks in 843 fetuses over a 5-year period. Ultrasound prediction of fetal gender was documented in 93.3% (770/843). The overall accuracy of diagnosis of fetal gender was 99.3% (765/770). Errors in diagnosis of gender were more likely to occur in the assessment of the female fetus. Such errors in diagnosis may be minimized by combining both tangential/transverse and sagittal views of the fetal perineum.

Risk of abnormal triple screen for Down syndrome is significantly higher in patients with female fetuses

“…With respect to this, even though our study did not have adequate power to detect a significant increase in rate of amniocentesis among female fetuses, a disturbing trend was indeed present in our data. Between 14 and 20 weeks' gestation, which is the interval when genetic amniocenteses for abnormal triple-screen results are usually performed, ultrasonography can identify fetal gender in 93 per cent of cases with an overall diagnostic accuracy of 99 per cent (Meagher and Davison, 1996). If our findings are confirmed by other studies, fetal gender should be searched for prior to genetic amniocentesis for abnormal triple screen, and when documented, it should be considered in the calculation of the Down syndrome risk.…”

Normal growth and development of fetal external genitalia demonstrated by sonography

“…The transverse plane can be used effectively after 14 weeks, and with a combination of tangential or transverse and sagittal views, fetal sex can be determined 93% of the time, with an accuracy of 99%, after 14 weeks' menstrual age. 9 Distinguishing between a small penis and a prominent clitoris and between minimally edematous labia and a small scrotum filled with spongy connective tissue may be difficult at the start of the second trimester. In our experience, visualization of the genital area is totally dependent on fetal position, and the best images are obtained on a tangential plane through the genital area after 14 weeks.…”

A pictorial guide for the second trimester ultrasound

“…Some departments will allow parents to know the gender of the fetus. If the external genitalia are to be visualised for sex determination then imaging in both mid‐sagittal and axial planes is recommended to minimise error 42 (Figures 48–49). …”