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Within 72 hours of unprotected intercourse, a birth
control pill can be taken to reduce the likelihood of pregnancy
resulting from this exposure.
A single dose of levonorgestrel 150 mcg, taken within 3 days of
exposure, will reduce the chance of resulting pregnancy from about 8% to
about 1%. The trade name for this product is the Plan B One-Step.
This dosage is accompanied by a 14% risk of significant nausea, so it’s
not a good choice for routine contraceptive use. But for emergency use,
it is pretty effective.
Following use of this medication, the next menstrual period may come on
time, or be a little early or a little late. 95% of women using this
medication will have their next periods within 7 days of the expected
time. The next period may be of average heaviness and duration, or it
may be heavier or lighter. If the next period is more than 7 days late,
a pregnancy test should be performed.
With progestin-only contraception taken continuously, there is a
somewhat increased risk of tubal ectopic pregnancy when the
contraception fails. No one knows whether that same risk applies to this
single dose of levonorgestrel or not. But to be safe, should there be an
emergency contraception failure, it’s a good idea to rule out ectopic
pregnancy.
In the past, there was some concern that emergency contraception might
cause abortions rather than simply prevent pregnancies, but those
concerns have since been proven to be unfounded with levonorgestrel. It
prevents pregnancy…it does not cause abortions. In the event the patient
is already pregnant when she takes this medication, it will not cause
her to lose the pregnancy and will also have no effect on the developing
fetus. It is believed to work by interfering with ovulation and
alterations in sperm transport.
While the single, 150 mcg levonorestrel, is probably the best choice for
emergency contraception, there are some other good alternatives.
Two Ovral birth control pills can be taken, followed 12 hours later by
two more Ovral pills. Should Ovral not be available, other good
alternatives include any levonorgestrel-containing birth control pill,
including:
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Lo-Ovral
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Nordette
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Levlen
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Levora
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Portia
If any of these pills are used, the dosing is 4 pills
immediately, followed by 4 more pills 12 hours later. This dosage will
reduce the risk of pregnancy from 8% to about 2%. So, it is somewhat
less effective than the single 150 mcg dose of levonorgestrel, and also
has a higher risk of nausea, approaching 50%.
The greatest experience with emergency contraception has been within the
72-hour window between exposure and taking the pill. Some studies find
emergency contraception is most effective the sooner it is initiated
within that 72 hours. Other studies find no difference in pregnancy
rates. A few studies have looked at the use of emergency contraception
for up to 120 hours after unprotected intercourse and find that it can
still be effective in some cases, even after 72 hours.
Contraindications to use of birth control pill based emergency
contraception are essentially the same as those for use of the birth
control pill in general, and are due to its estrogen content. Previous
stroke, undiagnosed uterine bleeding, heart attack, deep vein
thrombophlebitis and cancer of the breast or uterus are all
contraindications to sustained pill use. The extent to which they
represent risks in the context of emergency contraception is not known,
but should be weighed in evaluating a patient for emergency
contraceptive use.
However, for the single 150 mcg levonorgestrel dose, which contains no
estrogen, there are no contraindications.
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