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OVER THE MILLENNIA,<\/span>\u00a0<\/span>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\u2019ve got spermicides, sponges, intrauterine devices, pills, and implants to keep sperm and egg apart. There\u2019s just one problem: The people who want to avoid pregnancy aren\u2019t always using contraception.<\/p>\n \u201cThe big fact here is that about half of all pregnancies are unintended,\u201d says Deborah Anderson, a professor at Boston University Medical School who specializes in obstetrics, gynecology, and infectious diseases. \u201cEven though we have a really good method in hormonal contraception, it\u2019s not penetrating as well as we\u2019d like.\u201d<\/p>\n There are plenty of reasons why some people don\u2019t 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 daily pill or getting a shot every three months, or having a more invasive procedure to put in an implant. Other methods have their drawbacks, too: Some require partner consent, are easy to forget or use incorrectly in the heat of the moment, or have a lower success rate.<\/p>\n