Contraceptive reliability depends on two things: the reliability of the method and the inconstancies of human nature. Some unintended pregnancies come about because of method failure. Despite your best efforts and those of your partner, condoms can break, diaphragms and cervical caps can be dislodged during intercourse, and intrauterine devices can be expelled or fail to prevent implantation of the fertilized egg. These mishaps are built into the contraceptive method and are the fault of the method or product. All you can do is consistently use your contraceptive as directed. Other unintended pregnancies result from human failure: you forget to take your birth control pills for a couple of days; you leave your diaphragm in the drawer.

Statistics refer to “optimum use” or “best-expected effectiveness” to describe method failure and “typical use” or “estimated actual use” to include both method failure and human failure, or the relative success of the contraceptive in a real-world situation. These data are usually based on a year’s use and derive from interviews of couples who say that they are using a particular method of contraception as directed. It is difficult to come up with absolutely accurate numbers: people sometimes forget that they have used their birth control carelessly or not at all, so the statistics that supposedly describe method failure sometimes describe human failure.

Which contraceptives are the most reliable and the least reliable?

Starting with the most reliable and working down, the ones that you think about least work best: long-lasting hormonal contraceptives like Norplant and its successors and Depo-Provera, and surgical sterilization (either vasectomy or tubal ligation) are 99 percent reliable, in terms of both expected effectiveness and on-the-job effectiveness. This means that if 100 couples use these methods 100 percent of the time, only one of those couples will become pregnant by the end of the year. Next on the list of reliability are contraceptives that you don’t have to think about every time you need contraception: the pill and intrauterine devices. These are followed by condoms and diaphragms.

The least reliable form of contraception is no contraception at all. Also on the list of failure-prone methods are a couple of “folk” methods, which may have a reputation for effectiveness but in fact do not work. These methods include withdrawal (the man re-moves his penis from the woman’s vagina before ejaculating), douching, and breast-feeding. Other rumors falsely assert that you cannot get pregnant if you are having intercourse for the first time, or if the woman fails to have an orgasm.

Figure: The effectiveness of various contraceptive methods during a year of actual use

Figure: The effectiveness of various contraceptive methods during a year of actual use

Can you get pregnant if your partner withdraws before he ejaculates?

Withdrawal is one of the most commonly practiced “natural” methods of contraception, but it is risky. If your partner ejaculates only one drop of sperm before he withdraws, you can still become pregnant. Since that first drop is the most concentrated and contains the most vigorous sperm, your risk is substantial. Sperm can migrate upward even if they are not deposited in the vagina, so there is still a possibility of pregnancy even if the man ejaculates entirely outside the woman. Women have gotten pregnant from sperm on their thighs. And of course, in the passion of the moment, the man may not withdraw. On the other hand, if you and your partner suddenly have an attack of conscience in the midst of the sex act, withdrawal is better than nothing at all.

Why is douching with a spermicide after intercourse ineffective as a method of contraception?

The sperm en route to fertilizing the egg make their way past the cervix in about a minute, and continue into the uterus beyond the range of the spermicide in the douche within 20 minutes of intercourse. Even if you douche immediately after the act, you still have a chance of getting pregnant; as we have seen, the first sperm to reach the cervix are not only the fastest but the most potent and vigorous. One persistent rumor is that douching with cola kills sperm; this procedure may work in a test tube, but it is not an effective means of contraception.

Can you get pregnant when you are breast-feeding?

Although breast-feeding offers some protection for some women, it is unreliable. It may delay the return of fertility after pregnancy, but there is no way to know when ovulation will start again.

Heather, a midwife, likes to point out that midwives are very successful at breastfeeding. They know all the tricks and techniques, and they are very committed to it. Then she points to her two sons, Tim and Nick, who are ten months apart. Nick is living proof that breast-feeding does not prevent ovulation.

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