This is one of the most common questions of soon-to-be-moms.

A sonogram around 18 to 20 weeks from the last menstrual cycle can usually determine the baby’s sex.  The position of the baby during the ultrasound will determine how easy we can see the gender.  We usually can tell if the genitals look like a “hamburger” a girl, or a “hot dog” a boy.  There is no way to influence the baby’s position during the exam.

Amniocentesis or chorionic villus sampling are two very reliable methods of checking for the baby’s chromosomes.  We usually use these tests to check for abnormalities rather than just the gender.  The chorionic villus sampling may be done as early as 8 weeks and the amniocentesis at 14 weeks.  These tests are invasive and do carry some risks.

In the past few years there has been a new test that samples the mother’s blood and checks for the presence of fetal cells.  The free DNA is harvested and is used to test for 3 common chromosome abnormalities Trisomy 18, 21, and 13. It is approximately 99% accurate and can be performed at 10 weeks from the last menstrual period.   The test can also check the baby’s sex as well.

There are companies that offer paternity testing using the free circulating DNA. If accurate, this would be very useful in cases of disputed paternity.  The large lab companies such as LabCorp and Quest do not offer this type of testing at this time.