Sonographic Fetal Sex Determination

Abstract

Although sonographic fetal sex determination is feasible in most pregnancies, in some cases, it may pose difficulties. An attempt to determine the fetal sex should not be made before 12-weeks' gestation because this early, it is relatively inaccurate. After 13 weeks, it is accurate in 99% to 100% of cases without malformed external genitalia. Sonographic fetal sex determination in the late second trimester is based on direct visualization of the external genitalia, whereas in the late first and early second trimester, it is based mainly on the direction of the genital tubercle (the "sagittal sign"): downward direction of the genital tubercle indicates a female fetus and upward direction a male fetus. Other sonographic landmarks, such as the fetal scrotum, the midline raphe of the penis, the labial lines, the uterus, the descended testis, and the direction and origin of the fetal micturition jet in males may contribute to the correct determination of fetal sex. Inaccurate fetal sex determination may occur when the external genitalia are malformed. Three-dimensional ultrasound, although of generally limited diagnostic value for fetal sex determination, may aid in better definition of congenital malformations of the external genitalia.

Non-invasive prenatal diagnosis for fetal sex determination: benefits and disadvantages from the service users’ perspective

“…In the second and third trimesters, it is accurate in 499% of cases with normal genitalia. 2 Early ultrasound (12-14 weeks) is also a reliable option when performed at specialized centers. [3][4][5] Invasive testing, either using chorionic villus sampling from 11 weeks or amniocentesis from 15 weeks, [6][7][8] is also an option and allows definitive genetic diagnosis, but both techniques carry a small but significant miscarriage risk (B1%).…”

Maternal Intuition of Fetal Gender

“…19 NIPT and previously reported rates for second-trimester ultrasound [5][6][7][8] have comparable accuracy for gender determination; and both are far superior to maternal intuition. Using NIPT for gender determination does have practical limitations in that it requires venipuncture and additional expense, whereas ultrasound screening is recognized as standard of care regardless of whether gender identification takes place.…”

“…[6][7][8] The frequencies of the actual gender of the fetus were compared with observed frequencies of the maternal prediction of the gender using chi-squared test. For all statistical tests, an alpha of 0.05 was used as level of significance.…”

“…6 Three smaller studies reported respective accuracy rates of 100%, 99%-100% (in those without malformed external genitalia), and 98.8% (for female identification) and 100% (for male identification). [7][8][9] Locally, our obstetricians verify gender accuracy of the second-trimester ultrasound report at every delivery, and the rate of ultrasound accuracy for babies both screened as fetuses and delivered at our institution from 2013 through 2016 was 100% (unpublished data). Clearly, the reliability of ultrasound in this regard is well established.…”

Early Fetal Sex Determination using Cell-Free DNA in Micro-Volume of Maternal Plasma

“…An alternative method for sex determination is sonography. However, ultrasound evaluations for gender determination can only be conducted beginning in the second trimester [9]. First trimester sonography is often unreliable for sex determination due to the incomplete development of external genitalia [9].…”