If you’ve been using the Patch, Yaz or Yasmin, you’ve got to be wondering in the wake of this week’s news whether or not you should reconsider your choice of contraceptive. After all, the FDA has pretty much confirmed that these methods have a higher risk of blood clots than older birth control pills. By now, your mom has probably called you and told you to get off that nasty pill, your roommate may already have hidden next week’s patch from you, and you’re holding your breath waiting for a call back from your doctor, who’s probably fielding about a hundred calls today alone from worried pill and patch users
All you really want to know, though, is this –
What’s My Risk?
It’s an important question that deserves an answer and a conversation with your doctor. Let’s see if I can help inform that discussion. But first, you need to know a a bit about the subject at hand – blood clots.
What are Blood Clots?
Blood clots are blockages in the vein or artery that occurs when the blood coagulates in the blood vessels.
- A DVT (deep veinous thrombosis) occurs when blood coagulates in the veins of the leg or arm, where it causes pain, swelling and inflammation.
- A PE (pulmonary embolus) occurs when a clot forms in the lungs or breaks off from a DVT in the leg and gets lodged in the lung. PE’s causes shortness of breath and chest pain, and if large enough, lack of oxygen and even death.
DVTs and PEs are treated with blood thinners, which almost always work to dissolve the clot, although long term sequelae of the clot can occur.
- Clots to the heart and brain are exceedingly rare in young women. In birth control pill users, that risk is confined to women over 35 who smoke (and should not use estrogen containing hormonal birth control) and women who suffer from ischemic migraine with aura or underlying medical problems such as heart arrythmias that predispose them to stoke. (Women over 35 with regular migraine may also be at increased risk).
For the otherwise normal, healthy young woman on pills or the Patch, the risk for heart attack and stroke is just too rare to even begin to compare between users and non-users of these methods. And in fact, these risks have not been reliably shown to differ between currently marketed methods. So in this discussion we’re going to confine ourselves to talking about the risk from DVT, where the data appear to be a bit clearer.
How does Birth Control cause blood clots?
Birth control methods that contain estrogen increase the risks of blood clots by altering the delicate balance of clotting factors produced in the liver. In spite of this, however, most women taking estrogen don’t get clots. So, other factors must also be at play for a clot to form. Here are those other factors that we know and understand –
- Long plane flights and car rides. Prolonged immobilization can cause the blood to pool in the legs and clot. In my two decades of practice, almost every clot I’ve seen in my patients using estrogen containing birth control occurred after a long plane flight or car ride. That’s why it’s so important to get out of your seat and walk around on a long plane flight and make frequent stops on long car rides. And, unless they’re rising in business or first class with a seat that allows them to elevate their legs, I also advise all my patients taking estrogen to wear knee high travel compression socks, since studies have shown that these can lower clot risks due to plane travel.
- Genetic mutations / Family History. Some people are predisposed to clotting because they carry a mutation in their clotting factors, the most common of which is Factor V Leyden mutation, found in about 5% of the population. Women with such mutations should avoid estrogen. Some day we’ll have an inexpensive blood test to identify these women, but right now the best clue to a genetic mutation is a family history of blood clots. In families with such histories, genetic screening can be done in the affected individuals to identify the mutation and then screening of other family members to find out who is at risk.
- Obesity and smoking also increase the risks of clotting, in the arteries as well as the veins. Women over 35 who smoke should not use estrogen containing birth control.
- Surgery and hospitalization. Prolonged immobilization is the reason. Hospitals use compression stocking, pneumatic air pumping leg wraps and even low doses of blood thinners to prevent clots due to hospitalization. (God forbid they get the patients up and walking, but that takes nursing staff, and we’d rather spend the dollars on devices and drugs, don’t get me started…)
- Varicose veins. Birth control pills don’t cause varicose veins, but women who have varicosities (not superficial tiny spider veins, but large deep veins in the leg) have a higher risk of clotting due to pooling of the blood in the veins of the extremities.
- Advancing Age. The biggest factor associated with blood clot risks is age, with the elderly being at particularly high risk compared to younger individuals. However, pills are generally still safe to use in healthy women up to the age of menopause.
- Pregnancy. Perhaps the highest risk women take for blood clots is during pregnany, a time when your risk for clotting increases up to 5 times the rate in non-pregnant women. Here, the hormone of pregnancy, fluid shifts and edema in the legs are culprits. Researchers often compare the risks of hormonal birth control to the risk of pregnancy, although a better comparison is to compare it to the risk from using another method, combined with the risk of getting pregnant from that method if it is less effective.
The progestin component of pills
Scientists believe one of the factors affecting clot risk in one method vs another may be the progestin component.
- Northindrone (1st generation progestin)
- Levonogestrel (2nd generation progestin)
- Norgestimate, desogestrel, gestodene (3rd generation progestins)
- Dropeserinone (the progestin in Yaz)
Why? It’s not so clear, and some experts maintain that it makes no biologic sense that, estrogen dose being equal, progestins should impact clot risk at all. Despite this, research is mounting that lower clot risks seem to exist for first and second generation pills. Norgestimate pills may have a similarly low risk, perhaps because they are metabolized in the body to levonorgestrel. The progestin in the Patch is metabolized to norgestimate, but the higher estrgoen dose in the patch probably contributes to that method’s higher clot risk compared to norgestimate pills.
Now that you’re an expert on blood clots, let’s visualize the risks of your birth control
Because the risk of PE is so low, most studies either combined DVT and PE risk, or report on DVT risks alone, which is what I’m going to do. In general using the patch or yaz will increase your odds of a DVT by about 50% – that’s called relative risk of 1.5. Translating that to absolute risks is difficult, because the actual numbers of clots occurring in a given study depends on so many things, not the least of which is how they define that a clot has occurred. Each study the FDA examined used a slightly different methodology – some used pharmacy database prescriptions for blood thinners, some used claims-based diagnoses and others added confirmatory chart reviews. Each method has it’s biases, and none is perfect.
Absoute Risk DVT- Background
The background rate of clots among healthy women of reproductive age that I have seen most often quoted in the literature is about 4 per 10,000. This is your risk if you do not take hormonal birth control.The dots represent 10,000 women over a year’s time, with brown dots unaffected women and red dots those who have a DVT.
The risk in users of second generation pills containing levonorgestrel, or 3rd generation norgestimate pills is about 6 per 10,000. This is the risk that Ortho Evra and Yaz were compared to by the FDA. Here’s what that looks like –
DVT Risk – Ortho Evra Patch
Use of the patch increases that risk to 9 per 10,000. Here’s what that looks like –
In case you’re having trouble visualizing it, I’ll put it side-by-side.
So you can see, as reported to the FDA,there is an excess of about 3 cases of clots per 10,000 women using the patch compared with those using an older pill. If you’re on the patch, clot risk does not appear to diminish over time. So your excess risk remains about 3 per 10,000 as long as you use the patch.
DVT Risk – Yaz
The risk from using Yaz and Yasmin comes in pretty close to that of the patch, at around 10 per 10,0000. The risk for clots with Yaz decreases the longer you use it. So if you’ve been on it for over a year with no clot, your risk drops significantly for getting a clot in the future, to about 5 per 10,000.
DVT Risk -Pregnancy
Finally, what about the clot risk from pregnancy? Actually, that’s the highest risk of all – about 20 per 10,000 or 2 per 1,000.
What about the Ring? And pills containing desogestrel?
Excellent question. The FDA hasn’t addressed the clot risk with the Ring specifically outside of the FDA approval process. We do know that the ring imparts a significantly lower estrogen exposure than the patch and a 35 ug pill, but it’s unclear if that translates to a lower clot risk. The ring, after all, contains etononorgestrel, the active metabolite of desogestrel.
Pills containing desogestrel have come in at a risk of about double that of levonorgestrel pills, so I’m going to assume in the absence of data to prove otherwise that the risk of the ring would be about 8 per 10,000.
Why does it take so long for us to learn about these risks for methods that are already on the market?
Almost all newer contraceptives will have an undefined clot risk, since clinical trials are just too small to detect a statistically significant increase in clots, which as you know now are relatively uncommon events. It’s only when a method makes it out into the general population of millions of women that an increased clot risk becomes evident. (Of course, if the manufacturer does not report all the clots that occur in a trial, that’s a different story, and the subject of recent lawsuits related to Yaz.)
Your chance of dying from a blood clot related to your contraceptive is about one in a million. The chance you’ll get a blood clot is well below one percent no matter what method of birth control you use. In that very low risk range, your chance of a blood clot, in order of increasing risk, is –
Risk per 10,000*
|Non-hormonal. Not pregnant.||
4 per 10,000
|Levonorgestrel pills Noregstimate pills||
6 per 10,000
8 per 10,000
? 8 per 10,000
9 per 10,000
10 per 10,000
20 per 10,000
|* These numbers are estimates based on my best good faith interpretation of the literature and data presented to the FDA on 12/8-9/11. Better numbers may be forthcoming from the FDA or other sources in the future, but for now I need something for my patients and myself to work with. Margaret Polaneczky, MD|
Even if you take the pill or the patch, the odds are overwhelming that you’ll make it through your reproductive years without ever having a blood clot.
The risk of actually dying from a blood clot due to your hormonal birth control is about one in a million.
If you want to avoid the clot risk associated with estrogen containing contraceptives, you can use something else for birth control. Depo provera, the progestin only pill, Implanon, the IUD and barriers such as condoms and diaphragm are all reasonable choices.Each of these methods come with their own risks and benefit, and none is perfect.
Additional Reading from TBTAM
- Thoughts on the Contraceptive Path and Clot Risks
- FDA Ruling on the Ortho Evra Patch
- More on Ortho Evra and the FDA
- FDA addresses clot risks with Yasmin
- Yaz & Blood Clots – Two Studies point to Higher Risks
- Clotting up Office Hours with Talk About Clots
- Yaz maker to Women – “We Screwed Up”
- CVS/Caremark – Detailing for Bayer?