Is birth control pill 100 percent reliable?

By Lee Hye-jun

Approximately half of American women in their 20s use the birth control pill for contraception. It is easy to take and is known to be an almost 100 percent method for contraception. There are two forms of birth control pill: the combination of estrogen and progestin, and the mini-pill containing only progestin. The combination birth control pill prevents ovulation, thickens cervical mucus, and produces a uterine lining hostile to implantation. It is conventionally given daily for 21 days, stopped for 7 days, and then a new cycle begins — bleeding occurs during the pill-free interval. The mini-pill works similarly except that ovulation frequently occurs. It must be taken every day at the same time of day. In Korea, only the combination pill is available.

Surprisingly, 8.7 percent of women on the combination pill get pregnant during their first year taking it. This is lower than those using condoms (17.4 percent), withdrawal (18.4 percent), and periodic abstinence (25.3 percent), but higher than those who have implants (1 percent) and intrauterine devices (0.1 percent). The 8.7 percent failure rate is quite disappointing given the efforts women make not to miss a pill every single day. In fact, however, only 33 percent of women miss no pills in the first month and about one-third of the women miss three or more pills by the third month.

If a woman misses one pill, she should take a pill as soon as she remembers. No back-up method is needed. If she misses two pills in the first two weeks, she should take two pills a day for the next two days and use a backup for one week. If three or more pills are missed or two pills are missed in the third week, she should start a new package and use backup immediately for one week. If she has vomiting or diarrhea, the pills are unlikely to be absorbed appropriately so she needs a backup for at least seven days after the episode ends.

When to start the pill also matters. For a new user, the pill should be started no later than the fifth day of the menstrual cycle, preferably the first day. To start immediately regardless of cycle, a back-up method is recommended for the first week, such as condoms. In case she has had sexual relationship, a pregnancy test is warranted before starting treatment. For a current user, initiation of the next package should not be delayed longer than seven pill-free days.

Let us suppose a woman on the pill gets pregnant by mistake. Pregnancy itself is a concern, but a bigger concern arises when she continues the pill without realizing she is pregnant. Fortunately, the birth control pill does not increase the risk of major birth defects any more than the general rate of 2 to 3 percent.

Many readers may wonder why all this time they have thought the pill was nearly 100 percent effective. This is theoretically correct — the failure rate is only 0.3 percent if a woman takes the pills correctly. The 8.7 percent of failure rates are derived from actual users including those who take the pills inconsistently, incorrectly, or both. To be a perfect user, make it a habit. Place the pill where it can be easily spotted such as near the toothbrush, lotion, or pillow. Stick a reminder note on the refrigerator or mirror. If you still do not trust yourself, consider switching to other contraceptives such as an implant or intrauterine device. Then, you can forget about getting pregnant for a long time.

The writer is a doctor at Maria Fertility Hospital in Seoul. For further questions, send an email to the writer at hyejunlee@mariababy.com, or call the hospital’s English-speaking coordinator at 82 (Korea country code) 2 (Seoul area code) 2250-5577, or visit the hospital’s website, https://eng.mariababy.com/.