Ultrasound: accurate for determining baby's sex?

There is a disparity in the age and quality of some of the ultrasound equipment, as well as a difference in the experience level of technicians, which makes it difficult to accurately state one gestational age at which ultrasound can always detect fetal gender. Some of the reports in the literature are misleading because they use study protocols, which make use of the best and latest devices.

Even though studies are now reporting 100 percent accuracy in determining fetal gender between 11 to 16 weeks of gestation, in the average clinic situation, fetal gender identification is often not undertaken until at least 16 weeks, and is often not reliable until 20 to 24 weeks -- and this is when the baby cooperates fully!

In a study by whitlow, published in ultrasound in obstetrics & gynecology, a sample of 524 women underwent a detailed assessment of fetal anatomy at 11 to 14 weeks of gestation by means of transabdominal sonography and transvaginal sonography (26 percent). Fetal gender was identified and was confirmed at birth. The overall success of correctly assigning fetal gender increased with gestational age. At 11 weeks predictions were correct 46 percent of the time, at 12 weeks 75 percent, at 13 weeks 79 percent and at 14 weeks a 90 percent success rate was reached.

An article by efrat in the same volume (ultrasound in obstetrics & gynecology,may 1999,) assessed the accuracy of fetal sex determination at 11 to 14 weeks of gestation in 172 singleton pregnancies. The accuracy of sex determination increased with gestation from 70 percent at 11 weeks, to over 98 percent at 12 weeks and 100 percent at 13 weeks. Male fetuses were wrongly assigned as female in 56 percent of cases at 11 weeks, 3 percent at 12 weeks and 0 percent at 13 weeks. In contrast, only 5 percent of the female fetuses at 11 weeks were incorrectly assigned as male and this false-positive rate was 0 percent at 12 and 13 weeks.