Yes, "Lessons in Chemistry"'s Frog Pregnancy Test Used to Be a Thing

Watch out! This post contains spoilers.

"Lessons in Chemistry," which premiered its third episode on Oct. 20, isn't just a romantic drama; it also serves as a window into a historical moment that is often overlooked. Specifically, it shines a light on what women's lives were like in the 1950s, and the third episode does that in a pretty unique way.

In the episode, after experiencing some symptoms of pregnancy, Elizabeth (Brie Larson) sneaks into one of the Hastings labs that has frogs and steals two of them. In the bathroom, with one frog as the control and one as the experiment, she injects one frog with her urine. Hours later, the experimental frog has laid a beaker full of eggs.

But when I watched the show, I thought, Wait, is this real? I have never, ever heard about a frog pregnancy test in my life. So in case you're wondering the same thing, I did some digging into "Lesson in Chemistry"'s little historical quirk.

Back in the 1930s, it was discovered that frogs — specifically the African clawed frog, or Xenopus — could be used for pregnancy tests. Per Smithsonian Magazine, female frogs would be injected with a bit of urine in their hind leg. In the morning, if the person was pregnant, the frog's water would be dotted with eggs. The pregnancy hormone present in the urine started ovulation in the frog. This process was called the Hogben test.

Per Smithsonian, other animals have also historically been used as pregnancy tests, like mice and rabbits, but they had to be killed and examined to detect ovarian changes. Frogs could live through the process and be reused again and again.

Frog pregnancy tests weren't just an anomaly of Elizabeth's job; they were a main method used for testing pregnancy at the time. A patient's urine would be shipped to a laboratory, where it would be injected into a frog. According to Smithsonian, the frog pregnancy test was used until the 1960s, when a simpler, animal-free test was finally developed. Home pregnancy tests wouldn't be available until the 1970s, per The Atlantic.

Though the frog pregnancy test is no longer used, Xenopus are still often utilized in scientific experimentation.

"Lessons in Chemistry" premieres new episodes Fridays on Apple TV+.