A: It depends on what method is being used to determine gender. The most common way to detect fetal sex is an ultrasound, which uses sound waves to provide a visual image of your baby. During early fetal development, boy and girl babies look identical. It isn’t until around 14 to 15 weeks that fetal genitals can be clearly distinguished. Even then, it’s possible to make mistakes. With my first pregnancy, I was told at 16 weeks that I would be having a boy. I later learned that I was pregnant with a girl!

Other methods of detecting gender include chromosomal tests such as CVS and amniocentesis.

CVS (chorionic villus sampling) uses a small sample of the placenta to determine chromosomes. Physicians perform this test at approximately 10 to 11 weeks gestation and results are available by 12 or 13 weeks. Although the test is not done solely for gender identification, parents have the option to learn their child’s sex when they receive results.

Amniocentesis is usually done a few weeks later in pregnancy. In this test, amniotic fluid is sampled at approximately 16 weeks and used to determine fetal chromosomes. Results are quite accurate and are provided approximately two weeks after the test is performed.

There is at least one product on the market that claims to identify fetal sex earlier than standard medical tests. This product can be purchased directly by consumers and claims to reveal baby gender at five weeks gestation with 99.9 percent accuracy, using a few drops of maternal blood. The test purports to detect fetal DNA and allows eager moms to know the sex of their baby based on whether male chromosomes are detected in maternal blood.

While the ads sound convincing, there is no published scientific proof of the accuracy of the test. Published studies suggest that the accuracy varies widely between laboratories. The product is not regulated or approved by the Food and Drug Administration. And while the product website boasts testimonials from happy consumers, there are other websites where mothers attest to the inaccuracy of its results.

It’s important to remember that no test is 100 percent accurate. So you may wish to remain cautious and choose a gender-neutral theme for the nursery, waiting for the “big day” to get your final answer!