Clotting Up Office Hours with Talk about Clots

Thanks to the lawyers and the media, this is the conversation I had recently in my practice –

Patient: My mother has been seeing lawyers’ ads on TV about Yaz, and says I should stop taking it. I don’t want to get a blood clot.

Me: Are you experiencing any problems on the Yaz?

Patient: No.

Me: Is there a particular reason why you are taking Yaz vs another pill? (Looking through EMR) I think you had tried another pill and didn’t like how you felt, and wanted to try Yaz, correct?

Patient: Right. My room mate was on it and liked it. But now she’s worried too.

Me: So – let’s run the numbers, shall we?

Patient: OK.

Me: With some variation depending on which study you look at, the background annual risk for blood clots is around 3 per 10,000.

Patient: (nods) OK.

Me:According to one study, women who took Yasmin had a clot risk of about 8 per 10,000. We can probably assume the risk with Yaz is about 20% lower than Yasmin, since the estrogen dose is lower, so let’s call your risk 7 per 10,000. That’s a bit less than a tenth of a percent.

Patient: OK.

Me: Now, if that risk concerns you, we could change you to an older pill containing levonorgestrel. In that same study, women who took that pill had a risk of about 5 per 10,000.

Patient: (silence)

Me: But wait  –  You’ve been on Yaz for what, three years?

Patient: Four

Me: Okay, then, four. Now the biggest risk for blood clots is in the first year of pill use, so you’ve already established yourself as lower risk.  That would lower your risk to around 3 per 10,000. But if we change your pill, your risk will be about 2 per 10,000. So I guess the question is, is the excess annual risk of 1 per 10,000 , or one hundreth of a percent, enough to make you want to change your pill?

Patient: I’m just worried…

Me: Well, you could change to a progesterone only pill, or POP. That has no increased clot risk over the background rate. However, it does have about a 2% higher chance of pregnancy, and is more likely to fail if you miss a pill than the pills containing estrogen. So you need to be pretty perfect taking a progesterone only pill.

In addition, your acne was better on the combination pills – I can’t guarantee it will stay that way on the POP, but we can try. You can always go back. Most patients are pretty happy on POP’s.

Patient: I don’t think I want a POP.

Me: Do you want to go back onto condoms? or be fitted for a diaphragm?

Patient: No way! And I don’t want an IUD.

Me: So what shall we do?

Patient: What do you think I should do? I’m just worried…

Me: Okay, let’s change you to a pill containing one of the older progestins and see how your acne is. It’ll probably be just as good. But if you’re not happy, we’ll change you back.

Patient: (brightens) I like that. My mom will be happy.

Bottom Line

All estrogen containing birth control pills have a small but real increase in blood clot risks. How that risk compares between different pills is complicated, depends on which study you read, and none of the studies are perfect or definitive. In fact, the FDA has yet to make a distinction between standard dose pills (20-35 micrograms) based on clot risk, because the data are so problematic.

Meta-anlayses suggest that pills containing the older progestins such as levonorgestrel and norethindrone have lower clot risks than those containing new progestins gestodene, desogestrel and drosperinone. All of these studies to date have problems, but the data appear to be consistent across analyses. Few of the studies have included norgestimate, but those that have place its clot risk nearer to the older than the newer progestins.

Researchers are now looking at APC resistance as a surrogate marker of clot risk to help us better differentiate pills from one another, but this approach has not been universally accepted.

How to use this information clinically?

We really have no randomized trial data to inform contraceptive choice when it comes to clot risks. All of the studies published to data are problematic in that they do not consistently control for prescribing and diagnostic bias, and varying doses of estrogen between pills, another factor that strongly influences clot risks.

For most women, the choice between pills is made based on factors such as cost, convenience, cycle preferences, side effects and how you feel on one pill versus another. And advertising. At the moment, Yaz is the biggest selling pill, probably due to a large DTC campaign when it first came out.  (Bayer rightly got slapped by the FDA for over-hyping Yaz’s benefits in that campaign.)

If clot risks is your primary concern, there are non-estrogen methods you can use instead – Depo Provera, the IUD, condoms, Diaphragm and implanon. (But even some of these carry clot risk on the package insert, despite clinical trial data to support it.)

The bottom line is that no matter which combination birth control pill you use, you will have to accept a small increase in risks of clots.

What can you do to lower your risk of clots?

Since plane travel and long car rides can increase blood clot risks in anyone, consider wearing knee high travel socks for long plane flights and car rides. Ask for an aisle seat, stay hydrated and move about the plane frequently to avoid clotting. (You can more on avoiding clot risk from plane travel from the CDC.)

If you are at increased risk for clots, you should avoid all the estrogen-containing pills, no matter what dose or brand. 

And by the way, the risk for a blood clot in pregnancy is 1 in every 500-2000 pregnancies.  So it’s pretty much always safer to take a birth control pill than to be pregnant.