Over the millennia, people have come up with some very effective ways to avoid having babies. The ancient Egyptians and Greeks used linen sheaths and animal bladders, precursors to modern latex condoms and diaphragms. Now we’ve got spermicides, sponges, intrauterine devices, pills, and implants to keep sperm and egg apart. There’s just one problem: The people who want to avoid pregnancy aren’t always using contraception.
“The big fact here is that about half of all pregnancies are unintended,” says Deborah Anderson, a professor at Boston University Medical School who specializes in obstetrics, gynecology, and infectious diseases. “Even though we have a really good method in hormonal contraception, it’s not penetrating as well as we’d like.”
There are plenty of reasons why some people don’t want to use hormonal contraception: It requires a prescription, it can cause unpleasant side effects, it puts the onus of contraception on women, and it requires remembering a…