Pregnancies conceived in a cycle when levonorgesterel emergency contraception (Plan B) was used have no increased risk of adverse outcomes.
In a prospective study, researchers compared the outcomes of over 300 pregnancies in which Plan B was used during the cycle of conception to a similar number of pregnancies in which no exposure to Plan B occurred. Outcomes were the same, with about a 10% miscarriage rate and 1% rate of major malformations in both groups.
The study outcomes are not surprising. Plan B uses levonorgestrel, a progestin component of hormonal contraceptives for many years, long ago shown to be safe if pregnancy occurs despite its use. Despite the fact that plan B uses levonorgestrel doses that are higher than in traditional oral contraceptives, no adverse impact has been reported to date on pregnancies conceived despite Plan B use. Having yet another reassuring study is always good news.
A couple of things to remember when interpreting data from studies exploring the association between exposure to a medication or chemical and pregnancy outcome –
- The background rate of miscarriage traditionally was thought to be about 15%, but we now know can be as high as 50% if one includes very early miscarriages. Once a heartbeat is established on sonogram, that rate drops to 5% or less. So if you are studying pregnancy outcomes, how you diagnose the pregnancy will affect your miscarriage rate – will you use hcg levels or clinical diagnosis? If you enroll women in your study after 6 weeks, your miscarriage rate will be lower since the early miscarriers will not make it to your study.
- The background rate of birth defects in the general population is 3-4% – that includes major birth defects like spina bifida and minor birth defects like an extra digit.
- Subject recall of medication or other exposure can be skewed depending on the pregnancy outcome. If things go wrong, we tend to look back and remember everything that occurred, looking for a possible cause. If things went well, we tend to forget little things like that aspirin we took for that one-day headache. But retrospective studies are much much easier to do that prospective studies. So if you are looking for a link between an exposure and a birth defect, the first step is retrospective cohort analyses. If something comes up there, you need to confirm it in a prospective fashion (if you can).
1% major birth defect felt high for this relatively small population — that's 6 babies. I bet I've known more than 600 moms and at first thought I don't know Anyone with a disabled baby. A moment later I remembered my colleague Oleg in New York – Emanuel Syndrome; my friend Karen in LA – Netherton Syndrome; and my own dear young friend Emma with some sort of autistic-but-not syndrome. That's 3, not 6. But the numbers become real and I'm glad to see 'Plan B' doesn't add to the problem. Coincidentally my two friends each blog of their parenthood. I don't know what they would think about Plan B.
I'm a bit confused. Is pregnancy defined as implantation? (And how quickly can one tell that there's been implantation?)
So if plan B prevented implantation (in a given instance), then it's preventing pregnancy? (Because, I have to say, I looked at this and wondered if plan B is effective at preventing pregnancy if so many women got pregnant despite using it.)
Thanks 🙂
Andy –
The background birth defect rates are well-described and consistent. You may know 600 moms, but I'll bet that they are not georaphically, ethnically, or genetically as diverse as the general population from which these statistics are derived. Will have to check out those blogs.
Thanks.
Bardiac – ECP works primarily by delaying ovluation. If you've already ovulated, you're pregnant by the time you get to the pharmacy for Plan B, and it won't work.
It has been a real disappointment that ECP has not had the impact on unplanned pregnancy rates that we had hoped. Some of the reason for this may be that some women are taking more risks thinking it is there as a backup.
Thanks as always for your thoughtful comments.
Peggy
could the lack of immediate availability of plan B be part of the problem with pregnancies occurring anyway? anecdotally, anyway, i've read of drug stores not stocking it, pharmacists refusing to dispense it, etc.
i hadn't realized that plan B works mainly be delaying ovulation — so i guess that for a certain number of unlucky women, it won't work even if taken immediately. but for another group, it could make all the difference if they have an emergency prescription at home to take immediately, or if they have to run around for a couple days to get one.
also anecdotally, i remember that 30 years ago, the health center at my college was said to give emergency contraception on request, several birth control pills if i recall. i have no idea of studies were done of either that off-label use or long-term consequences, but have the impression that it was thought to be safe. the controversy over plan B did not make a lot of sense to me, because i believe that something similar was in use for decades.
interesting about how birth defect rates seem high compared to our personal experiences, but i suspect that is because seriously disabled children tend not to be very involved with mainstream public life. we don't see them much.
i know three wonderful families with seriously developmentally impaired children; each tried caring for them at home, and ended up making the heartbreaking decision of placing them where they could get the extensive care they need. one little girl was born with a defective liver and needed transplants. a couple of children with club feet, another with a cleft lip. a second cousin's daughter has lifelong cognitive, developmental, and physical problems. a friend whose malformed baby was stillborn at 8+ months. many who had miscarriages.
Thanks for the great post! I am planning on writing a letter of complaint to the editors of one of my embryology textbooks I used to study for boards, in which they completely mischaracterize the method of action of Plan B. Of course, they describe it as an abortifacient. Even before this recent study, they should have been aware that is not the method of action. As you said, it delays ovulation, which they did not even mention.
I thought there was a comparison study of groups given Plan B to have at home for future issues, compared to a control group of women told to pick it up at the pharmacy (status quo), and did not find an increase in risky sex behavior.
I think it is more likely that people have poor access. Also, the stigma and misinformation associated with Plan B may have no small part in people not using it effectively or frequently enough.
Oh, and thanks for pointing out the difference between medical research and "people I know". Nothing wrong with using people you know as information about health, but it definitely is not more accurate than scientifically measured incidence statistics in a study or background incidence in a population.
There is a big difference between anecdotal stories and medical research. Both have a place in the discussion, but many lay people try to critique medical research by saying it disagrees with some anecdotal experience of theirs, and don't understand that both don't have equal validity.
Sorry to last commenter, but I removed your comment as it had confusing medical information and a link to a site that was confusing as well, and had some incorrect information about condoms and spermacide – FYI – spermacidal lubricated condoms are NOT recommended as spermacides increase the risk for HIV transmission if the condom breaks.