Dr. Singh, my intern, presented the case: “Fifty-one-year-old woman complaining of right calf pain and swelling. Flew back from London two days ago. On birth control pills for 20 years. Sister recently developed a thigh clot after starting the pill.”
I turned to our patient. “Mrs. Watson, why are you on birth control pills?”
With the tone adults use for dense 2-year-olds, she explained, “Um, that would be to avoid having babies, doctor.”
Her husband, a hearty Brit, guffawed. I laughed along with him.
“Sometimes they’re used to regularize menstrual cycles or treat severe cramps,” I replied, trying to sound medical.
“No, none of that,” she replied, her eyes still twinkling. “My doctor was thinking of taking me off them soon.”
I kept my peace. Dr. Singh continued: “No other medical problems. Currently on prednisone [a steroid] for a cat allergy. Works at a financial firm downtown.”
I stopped him. “How long have you been on the prednisone?” I asked her.
“Oh, a doctor in London prescribed it for my cat allergy. I’m only taking 10 milligrams a day. All better now,” she beamed.
That’s an odd dose, I thought.
Dr. Singh continued. “On exam, the right calf is swollen and tender. The thigh appears normal. No respiratory complaints, oxygen saturation is normal, and the lungs sound clear.”
I pressed gently on Mrs. Watson’s calf.
“Ow!” she cried. “That does hurt.”
“I’m so sorry. Even a little pressure like that?” I asked. She nodded.
“Diagnosis?” I asked Dr. Singh.
He shrugged. “Obvious: DVT.”
If there was ever a disease of modern living, deep vein thrombosis (DVT) is it. A thrombosis is a clot formation. Unlike our arboreal primate cousins, Homo sapiens is built to roam vast stretches of savanna. When it comes to endurance running, we are among the best in the animal kingdom. The only tailless bipeds on the planet, we are long-distance-running machines, with the great veins in our oversize legs thriving on brisk blood flow and the pumping action of our muscles.
Stick us behind a desk or wedge us into economy class, however, and trouble looms: Blood in the veins pools, providing a stagnant milieu for our coagulation system—which works so beautifully to stanch cuts and gorings incurred in a hunt—to go awry. Add obesity and a dose of cigarettes and the lithe runners of the Serengeti Plain turn into champion clot formers. It is no accident that two of our top three killers are heart attacks and strokes.
And then there’s the role of another modern invention: birth control pills. These hormone-laden pills (containing estrogen and progestin) pretty much defined the sexual liberation of the ’60s, but the pills’ downside—excess clotting—wasn’t widely recognized until the ’70s. Although lowering the dose of estrogen and progestin helped, second-generation pills still triple or quadruple the risk of DVT. Third-generation pills appear to be even riskier.
With 100 million women on birth control pills worldwide, the odds of a blood clot can be cast with some precision. A healthy woman in her twenties has less than a 1-in-10,000 chance per year of developing a DVT. Being on the pill ups the risk to 3 or 4 in 10,000. Age dramatically alters the equation: A woman over 40 has a 1-in-1,000 chance, and the pill has the same multiplier effect in this group. (To be fair, the risks of pregnancy far outweigh the risks of the pill, except in high-risk women.)
DVT risk factors don’t stack, they multiply. Take plane travel. The risk for a flier on oral contraceptives soars 14-fold. In one scary study out of Charles de Gaulle Airport in Paris, researchers performing on-site ultrasounds found that among travelers who had spent more than eight hours in the air, 10 percent had asymptomatic clots lurking in their leg veins.