Is it a boy or a girl? Even if you’re sick of getting asked by friends and family, you probably want to know yourself. Doctors can determine the sex of a fetus at 9 weeks by blood test and about 14 weeks by ultrasound, though there is room for error. For earlier predictions, many parents turn to unscientific folk methods, such as the Chinese lunar calendar. Spoiler alert: These are almost always BS. Is the baking soda gender test any better?
There is some chemistry involved, but, we promise, no deeper science. First, get some baking soda — the first step in many home-brewed science experiments. Next, the pregnant person collects their urine. Finally, combine the two. The idea here is that having a boy will change hormones in the body and make the urine more acidic, and adding the acidic pee to the basic baking soda will make it fizz as they chemically react. Having a girl, so the thinking goes, means less acidic pee and no chemical reaction.
On the science end, it is true that adding an acid to baking soda will make it fizz and bubble. However, there is no evidence that the sex of a developing fetus affects the acidity of the urine of the pregnant person. “Unfortunately, the science involved here is exclusively in the chemical reaction of acids and bases and not in predicting the chromosomal makeup that identifies the sex of a child,” Kim Tustison, professor of obstetrics and gynecology at the University of California, Riverside School of Medicine, told What To Expect.
In other words, the chance the baking soda gender test gives you the correct answer is just that — random chance. It’s no better than a coin toss. (Even if the test told you what’s between your baby’s legs, that would be their sex, not their gender.)
However, there are other factors that determine how acidic your pee is and thus whether it will make baking soda bubble. Diet and hydration levels can affect the pH of your urine. Urinary tract infections, kidney stones, and medication can make it change too. “Growing a new human may change aspects of a woman’s metabolism, which may alter the acidity of urine, but there are no variances, based on whether the expected child is male or female,” Tustison said.
If you want to know your baby’s sex, ultrasound can be used to predict it as early as 11 weeks, though it becomes more reliable later as the fetus’s genitals develop. Most pregnant people don’t get get the ultrasound that reveals sex until 20 weeks into the pregnancy. Blood tests can be accurate as early as seven weeks, though some doctors recommend it only for testing for sex-linked genetic conditions because some expecting parents may abort a fetus if they were hoping for a different sex. Other more invasive options include chorionic villus sampling and amniocentesis, which do carry risk of ending the pregnancy and are only done for medical reasons.