When can I find out the gender of a child?
These days, there are two ways to learn the sex of your child before he or she is born: an ultrasound and a blood test.
Ultrasound
Even though a boy’s penis and scrotum start to form around 11 weeks, they are impossible to see on an ultrasound. To determine the sex of a child by ultrasound, you must wait until week 20, when the genitals are easy to recognize.
Blood test
Using a blood test, you can determine the sex of your child much earlier — week 7. The technique is based on the identification of the male Y-chromosome in the blood of the expectant mother. Separate cellular elements of the baby’s blood (nuclear red blood cells and white blood cells) and the placenta penetrate the mother’s blood, so fetal DNA (baby’s DNA) can make up to 10% of the mother’s plasma. How accurate the test is depends on when it's done: in weeks 7 to 12, it detects the Y chromosome in about 95 out of 100 boys, which means about 5 out of 100 tests may miss it; before week 7, it detects it in only about 75 out of 100 [1].
For ethical reasons, doctors do not provide this test simply for curiosity — that is, to exclude the possibility of a couple of sex-selective abortion. Normally, this test is run for expectant mothers who have genetic diseases associated with the sex of the child. Hemophilia, for example, is transmitted through the female line exclusively to boys. Another reason this test may be given is to determine the Rh factor of the child — to prevent a conflict with an Rh negative mother.
