Not many babies are born when their parents are on vacation, but many babies are conceived when their parents are out of town. Any kind of contraception, but especially the Pill, requires planning ahead before traveling abroad.
Women who take a progesterone-only "mini-Pill" because they are nursing or because they want to lower the risk of deep vein thrombosis (DVT) on a flight need to be especially aware of the Seven Day Rule:
If a Pill is more than three hours late, pregnancy is possible for the next seven days.
Progesterone-only Pills have to be taken on a strict schedule, adjusted for the time zones crossed. For instance, if a woman who lives in Seattle usually takes her Pill at noon and she flies to Hong Kong (nine time zones west), she still has to take the Pill at noon Seattle time, which in Hong Kong is 3 a.m. (The calendar date doesn't make a difference.)
Combined estrogen and progesterone contraceptives allow a little more leeway. Women should follow package instructions, or the Twelve Hour Rule:
If you are less than twelve hours late taking the Pill (on your home time), take the delayed pill at once, and then return to your normal schedule the next day at your new location. A woman from Seattle who usually takes her combination Pill at noon in Seattle can also take it at noon in Hong Kong. That's because there's only nine hours time difference. She still has to take it at noon Seattle time on the flight. For this purpose, it's helpful to have a watch on home time.
If you are more than twelve hours late taking the pill, however, the same Seven Day Rule kicks in.
If you are more than twelve hours late (by your home clock) with your daily Pill, take the most recently delayed pill at once, continue the rest of the package, and abstain from intercourse (or use other methods of contraception) for the next seven days. If there are more than seven pills left in the package, continue your normal schedule, taking a seven-day break when you finish the package. If there are fewer than seven pills in the package, be sure to take the Pill for at least the next seven days, breaking open a new package, and taking your seven-day break at least seven days after the last skipped pill.
Of course, even if you are keeping track of time, there can be other problems.
If you experience vomiting less than three hours after taking the Pill, take a replacement pill from a spare packet. If the replacement pill doesn't stay down, either, follow the same rules as for a missed pill, above. Diarrhea usually will not interfere with absorption of contraceptives unless it is very severe. If there is severe diarrhea within eight hours of taking the pill, however, follow the "seven-day rule" as above. And if you take the antibiotic Doxycycline, the effectiveness of the combined estrogen-progesterone Pill can be diminished for up to three weeks.
Injectable contraceptives (Depo-Provera, Noristerat) aren't affected by time zones or gastic upset. As birth control Depo-Provera is a more reliable method during international travel.
Robert Rister has also written on whether the rhythm method works on vacation at his Savvy Natural Healer website.
