How common is delayed menses after taking Plan B?
Updated: May 24
“I recently saw a 26 yr old female whose LMP was 3/13/22, she had unprotected sex 3/27/22 and took Plan B 3/28/22, experienced spotting 4/4/22 and has not had a regular menses since 3/13/22. Pregnancy test done 5/16/22 and negative. What is the recommended time frame to return for a repeat pregnancy test and how common is it for delayed menses post Plan B?”
Plan B is licensed for use within three days of unprotected intercourse, although it has been shown to work if taken up to five days – which is the common recommendation. The sooner it is taken, the more effective it is. Your patient took it quickly, and it appears she has not become pregnant from her unprotected intercourse on 3/27/2022.
If she had become pregnant on 3/27/22, the test on 5/16/22 would have picked it up. A sensitive pregnancy test is usually positive two weeks after conception, but since that is very early, testing may be repeated weekly in the early weeks to be sure, adding time to detect increasing levels of HCG. Since ~7 weeks passed between her intercourse and pregnancy testing, it appears she did not get pregnant from that act.
If there is concern about the test itself, it may be repeated using a different test or technology (e.g., use serum when urine done initially), but you would not need to wait a certain time frame. Occasionally there are early false negative urine tests, that are positive with serum testing.
Typically, the next menses occurs within one week of the usual anticipated date. But, irregular bleeding or spotting may also occur such as in your patient, and that is not unusual. Since Plan B works by blocking the LH surge, and ovulation, it may delay or changes the next menses. You are right to be concerned with persistent amenorrhea and to rule out pregnancy, but I’d be more worried it occurred from a later act of intercourse.
It is important for people using Plan B to know that it will not protect from additional acts of unprotected intercourse in that cycle, so if she continued to have sex without birth control, she could have become pregnant from a later act – which would be a reason to prompt more pregnancy testing.
Has she used any other method of contraception since taking Plan B? A pregnancy scare and taking Plan B is a good reason to consider starting an ongoing effective method.
Usual counseling points regarding menses and EC
Patient should expect a menses within three weeks of using EC. Onset may be earlier or later than usual. If there is no menses within three weeks of using Plan B- a pregnancy test is recommended. If there is irregular bleeding or abdominal pain, a test and perhaps an evaluation, is indicated to rule out an ectopic pregnancy.
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