Once upon a time, an expecting mother had to wait until the birth of her child to learn the sex of her baby. Until then, parents only had "old wives' tales" to help them predict, and you've probably heard them all by now. Some are especially troubling to hear, like the tale that you're obviously carrying a girl because you're looking run down and your baby is stealing all of your beauty in utero. But what exactly is your doctor seeing in there? Turns out, how your OB can tell you're having a girl has nothing to do with your "beauty" and can be figured out pretty simply. (As long as your baby cooperates.)
Over email, Dr. Yen Tran, OB-GYN, of Orange Coast Memorial Medical Center in Fountain Valley, California, tells Romper that "non-invasive prenatal testing by blood work" can be performed as early as 10 weeks into your pregnancy. In addition to revealing your baby's sex, such a test would determine whether or not the baby has Down syndrome, trisomy 18 and 13, and other microdeletions. (It's worth mentioning that the decision to test for chromosomal abnormalities is a very personal one. Even if your main reason for getting prenatal blood testing is to discover your baby's sex, it may be helpful to think through the other results of the test and decide in advance what you would do in each possible scenario.)
Tran also describes the other two options to determine your baby's sex as ultrasound and amniocentesis, the latter of which consists of a "long needle poking through a woman's abdomen." However, Tran notes that "doctors usually don't do invasive testing to determine the sex of baby." And if you thought your OB used the old wives' tale about a baby's heartbeat determining the sex, Tran debunks that theory. When asked if there is any scientific or medical evidence to back up the idea that female babies have a faster heartbeat in utero, she simply says, "No."
Most likely, you'll have an ultrasound to determine your baby's sex. So what exactly is your OB looking for in there? Romper spoke with Jane Frederick, M.D., an internationally noted specialist in Reproductive Endocrinology and Infertility at Saddleback Memorial Medical Center in Laguna Hills, California, who explains:
"Ultrasound is 80 percent accurate. In the ultrasound, you can only see the penis. Therefore, if there is no penis seen, then assume it must be a girl. Typically, you are able to determine the baby’s gender accurately at around 20 weeks. Although with new technology advances in ultrasound machines, like 3D ultrasounds, some are able to determine the gender as early as 14 weeks."
If you want to practice interpreting the ultrasound screen before your appointment, Parents magazine has clear pictures of boy and girl genitals at 18 weeks. Frederick is right that the penis is easier to spot than the vagina, but if your baby cooperates with a between-the-legs shot, you can probably guess before your OB announces your baby's sex. For what it's worth, the ultrasound tech at my daughter's 20-week scan told me to look for a hamburger-like shape.
Overall, if you want your OB to tell you if you're having a girl, your best options are to opt for early prenatal blood testing or wait until the sex can be determined with an ultrasound. But until you know for sure, there's no harm in trying to guess your baby's sex based on your pregnancy cravings, the shape of your belly, and all the other tricks and tips your friends and family will no doubt come up with. In our information-saturated age, it's easy to forget that not knowing can be just as much fun as picking out specific nursery decor in advance.