Whats the accuracy of sonographic
The objective of this study was to examine the accuracy of fetal gender prediction at a routine first trimester scan. Pregnant women, from an unselected population around the world were recruited for this study. They agreed to the study, to examine the accuracy of fetal gender prediction, at a routine first trimester scan for detailed assessment of fetal anatomy and nuchal thickness measurement.
The clinical value of early ultrasound determination of fetal sex includes, confirmation of zygosity and analysis of chorionic villous sampling in twin pregnancies, early information for demanding parents and a powerfull method to decide whether to carry out prenatal invasive testing in pregnancies at risk of sex-linked genetic disorders, because it would be unnecessary in pregnancies with female fetuses.
The examinations were made with the use of normal two-dimensional (2D), three-dimensional (3D), transabdominal and transvaginal sonography data. Sex confirmation data was obtained postnatally from hospital registries, parents information or by ultrasound performed after 25 weeks of gestation.
Some gender determination was performed as a part of the sonographic examination preceding genetic amniocentesis or chorionic villus sampling. The results were compared with the gender at birth or with fetal karyotype results obtained from amniotic fluid cells or chorionic villus sampling.
What is a sagittal view? (vertical cut away slice of the body as seen from its side)
The fetal gender was assigned as male if the angle of the genital tubercle to a horizontal line through the lumbosacral skin surface (lower portion of the spine) was greater than 30 degrees and female when the genital tubercle was parallel or convergent (less than 10 degrees) to the horizontal line.
Details of 'Angle of the 30 degrees' study
In some of the study groups, when the angle of the genital tubercle was an intermediate angle of 10 to 30 degrees the fetal gender was not determined.
Out of a total of 1619 pregnancies; gender was assigned and confirmed in 1424. The table below shows the results in so far for accuracy of fetal gender prediction at a routine first trimester scan.
Prenatal gender assignment by ultrasound has a high accuracy rate at 12 to 14 weeks. At 11 weeks there was an error rate of 50% and only 14/100 assigned correct male gender. In the male fetuses after 12 weeks, there was a significant increase in the angle of the genital tubercle from the horizontal. The accuracy of sex determination increased with gestation.
Details of Embryo genital development
Our results suggest that first trimester sex determination by routine ultrasound reaches the best accuracy at the 13th week of gestation.
Whilst the accuracy of sonographic determination of fetal gender at 11 to 14 weeks is good, it still falls significantly short of invasive karyotyping tests.
Our results suggest that a final decision on invasive testing for sex-linked conditions should be undertaken only after 12 weeks of gestation.
Prenatal gender assignment by ultrasound has a high accuracy rate at 12 to 14 weeks. These results indicate that invasive testing can probably be carried out in fetuses identified as males at this gestational age. However, in fetuses identified as female at a CRL of greater 62.6 mm, despite the relatively high 91.5% accuracy rate, the decision regarding invasive testing should be postponed until a higher CRL is achieved.
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