I Was 26, on Birth Control, and 12 Hours From a Pulmonary Embolism

26, on oral contraceptives, 12 hours sitting daily, postoperative pulmonary embolism: how the risks stacked up

When Xiaoyu returned to Hangzhou, her right leg felt wrong first.

It ached, felt heavy, and gave a dull pain. She thought it was from a week in the car. During that trip, she spent 5 to 12 hours a day in a vehicle, crossed several cities, and rarely stretched her legs. Back in Hangzhou, she had an elective minor surgery. A few days later, the ache had not gone away. Her chest felt tight, and her breathing became short.

She remembered the doctor’s warning when the contraceptive was prescribed: watch for blood clot risk.

At Zhejiang Hospital, tests found deep vein thrombosis in her right lower limb. Part of the clot had entered the pulmonary artery, causing a pulmonary embolism.

She was 26. A tightly packed vacation and a minor operation had nearly killed her.

Twelve hours in a car a day, never stretching her legs

Travel lasting more than 6 hours is an independent risk factor for VTE under the 2023 IUP consensus. Xiaoyu spent 5 to 12 hours a day in a car, far past that threshold.

When you sit for hours, the calf muscle pump nearly stops. Venous return depends on calf muscle contraction. If the muscles do not move, blood pools in the deep veins of the calf. Slow flow lets clotting factors collect, which gives a clot a place to start.

This was more than car fatigue. For every hour of sedentary sitting, deep vein thrombosis risk rises by about 10%. After 4 hours of travel, VTE risk roughly doubles.

The estrogen in the pill had shifted her blood toward clotting

Xiaoyu had taken oral contraceptives for several months.

Estrogen in combined oral contraceptives changes liver synthesis. It raises prothrombin and factor VIII and lowers antithrombin and protein S. The balance tips toward clotting.

For most young women without other risks, the absolute risk is low. A Danish cohort study found about 6 venous thrombosis cases per 10,000 woman-years among current oral contraceptive users, compared with about 3 among non-users. Levonorgestrel-containing combined pills add about 10 to 15 venous thrombosis events per 100,000 women per year. That is lower than the VTE risk of pregnancy and childbirth.

But Xiaoyu had other risks too.

Surgery added the third risk factor

After returning to Hangzhou, she had an elective minor operation.

Surgery activates coagulation. Tissue factor is released, the vascular endothelium is damaged, and the body starts its hemostatic response. In patients on oral contraceptives, postoperative thromboembolism risk rises about 3 to 4 times.

Three factors were now present:

• Blood flow stasis: 12 hours a day in a car.

• Vascular injury: surgical trauma.

• Hypercoagulability: long-term oral contraceptive use.

All three thrombosis conditions appeared within a short period. One factor alone rarely causes a clot. When they stack, the risk multiplies.

The aching right leg was a clot signal

The typical signs of lower-extremity deep vein thrombosis are sudden swelling, aching, or pain in one leg, or a visible difference in thickness between the legs. Xiaoyu’s aching, heavy, dull right leg was already a signal.

The greater danger comes when the clot breaks off. If it travels into the pulmonary artery, it causes pulmonary embolism. Symptoms include chest tightness, shortness of breath, chest pain, and palpitations. Severe cases can bring fainting or shock.

A case report of 8 young contraceptive users with fatal thromboembolic complications found that 5 died of pulmonary embolism. Their average age was 24. Four of the 5 had worsening lower chest pain and exertional dyspnea before onset. Those early symptoms are often mistaken for tiredness, a cold, or poor sleep.

Risk numbers: low alone, higher when combined

The numbers:

• Oral contraceptives: VTE risk is about 4 times that of the general population.

• Long-haul flights: VTE risk is about 2 times that of the general population.

• Both together: one study found a 14-fold risk.

That study looked at air travel, so it does not apply directly to cars and high-speed rail. But long car and rail journeys also cause prolonged sitting and reduced lower-limb activity. More than 12 hours a day in a car is severe immobilization.

Oral contraceptive risk also depends on how long you take it and which drug you take. VTE risk is highest in the first year, with a rate ratio of 4.17. It falls to 2.98 at 1 to 4 years and 2.76 after more than 4 years. Drospirenone-containing pills carry a higher VTE risk than levonorgestrel-containing pills, with a rate ratio of 1.64.

These numbers do not mean everyone should stop the pill. Risk depends on context.

Four commonly missed precautions

First, no screening for high-risk thrombotic factors before starting the medication.

Many women buy oral contraceptives on their own and take them long term without checking for a history of thrombosis, family history, smoking, high blood pressure, obesity, and other conditions. Women with a history of thrombosis, a family history of thrombosis, migraine with aura, or severe hypertension may not be suitable for estrogen-containing contraceptives.

Second, not asking a doctor before long-distance travel.

Before planned travel of more than 4 to 6 hours, ask whether the pill needs adjustment or whether preventive measures are needed. Most people remember nausea, headache, and vaginal bleeding, but not blood clots.

Third, not stopping the medication before surgery.

The drug label recommends stopping at least 4 weeks before major surgery or other surgery that raises VTE risk, and staying off it until 2 weeks after surgery. The MSD Manual says oral contraceptives are usually stopped 1 month before surgery and resumed 1 month after. The British National Formulary also recommends stopping combined oral contraceptives 4 weeks before major surgery or planned immobilization.

Xiaoyu had surgery right after long-distance travel. If the preoperative assessment had asked whether she was taking contraceptive pills, doctors could have addressed the risk earlier.

Fourth, not recognizing the signals the body sends.

Watch for swelling, aching, or pain in one leg; a difference in thickness between the legs; chest tightness, shortness of breath, unexplained difficulty breathing; chest pain, coughing up blood, or fainting. If any one appears, seek medical care immediately. Do not watch and wait.

If you are taking the pill: before travel and surgery

During travel:

• Move once every 30 to 60 minutes. If you can get up, walk around.

• Do ankle pumps while sitting. Flex the toes toward you, then point them away. Hold each for 5 to 10 seconds. Repeat 10 to 15 sets per hour.

• Drink a few sips of water every hour. Aim for 1,500 to 2,000 mL of total daily fluid. Limit coffee, strong tea, and alcohol.

• High-risk individuals may wear medical graduated compression stockings, 15 to 30 mmHg, under a doctor’s guidance.

When planning surgery:

• Tell your doctor in advance that you are taking oral contraceptives.

• Ask your doctor when to stop. It is usually 3 to 4 weeks before surgery.

• You usually restart at least 2 weeks after surgery. Some doctors say 1 month.

• Do not stop on your own. Arrange an alternative contraceptive method at the same time.

Daily use:

• Complete a thrombosis risk screening before starting the medication.

• Avoid long-term NSAID use with the pill. The combination raises VTE risk.

• If one-sided leg swelling, chest tightness, or shortness of breath appears, seek medical care immediately.

Xiaoyu recovered and was discharged after anticoagulation therapy and close monitoring. The nurse handed her the anticoagulant and said: Next time before a long car trip, come ask first.

She nodded and put the pill box into her bag.