Today's expectant parents can find out the sex of their child well before it is born. There are two basic ways of determining fetal sex. One is by analyzing genetic sex, based on the information encoded in the sex chromosomes. The present techniques for doing this in the first and second trimesters, chorionic villus sampling and amniocentesis, each incur a risk of miscarriage. In families where there is an inherited disease such as hemophilia that appears only in males, determination of fetal sex might be important.
The rate of correct diagnosis of genetic sex by study of the chromosomes is dose to 100 percent. The diagnosis of anatomic sex on the basis of genetic sex cannot be 100 percent, however, since there are rare instances in which the anatomic and genetic sex are not identical. When such a difference exists, anatomic sex generally determines the gender of the individual.
Sonography-using ultrasound to look at the appearance of internal and external genitalia eliminates the early pregnancy risk of spontaneous abortion or miscarriage that occurs with chorionic villus sampling or amniocentesis. However, if a decision on abortion for sex-linked genetic disorders is at stake, an error rate of approximately 10 percent seriously limits its usefulness.
Although prospective parents may be tempted to have an ultrasound merely to satisfy their curiosity about the sex of their baby, this practice is discouraged as ultrasound, like most medical interventions, cannot be determined to be completely safe. Its use requires a benefit beyond mere curiosity. The American Institute of Ultrasound in Medicine stated in May 1999, "The use of either two-dimensional (2D) or three-dimensional (3D) ultrasound to only view the fetus, obtain a picture of the fetus or determine the fetal gender without a medical indication is inappropriate and contrary to responsible medical practice."
Fetal sex also can be ascertained in the second trimester by fetoscopy, The risks of fetal injury with this technique are considerable and failure to see the genitalia frequent. Again, the method is not used purely to determine sex.
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