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Long-Haul Flights in Pregnancy: DVT Risk

Flying when you're pregnant is something many women do without any problems — but it's worth understanding the specific risks and how to manage them. Pregnancy itself increases your risk of developing a deep vein thrombosis (DVT, a blood clot usually in the leg), and long-haul flights add another layer of risk on top. The good news is that most of this risk can be managed sensibly with some straightforward precautions.

Why Pregnancy Increases DVT Risk

DVT happens when a blood clot forms in a deep vein, most commonly in the calf or thigh. During pregnancy, your blood becomes more likely to clot — this is a natural protective mechanism to reduce bleeding during birth, but it does raise your background risk of clots forming where they shouldn't.

Long periods of sitting still — as on a long flight — slow the flow of blood through the veins in your legs, which further increases the chance of a clot forming. Pregnancy also causes your growing uterus to put pressure on the veins returning blood from your lower body.

A DVT itself is serious, but the greater danger is if part of the clot breaks off and travels to the lungs (a pulmonary embolism), which can be life-threatening. This is why it's important to take the risk seriously — not to avoid flying altogether, but to take sensible steps.

Reducing DVT Risk

The following measures are recommended for all pregnant women on long-haul flights (generally considered to be flights of four hours or more):
  • Wear graduated compression stockings — class 1 compression socks (15–20 mmHg) help keep blood moving in your lower legs. Wear them from before you board until you arrive at your destination. You can buy these from pharmacies without a prescription.
  • Get up and walk the aisle regularly — aim to walk for a few minutes every one to two hours during the flight. Choose an aisle seat to make this easier.
  • Do in-seat exercises — when you can't get up, flex and extend your ankles, circle your feet, and pump your calf muscles. These simple movements help keep blood circulating.
  • Stay well hydrated — cabin air is very dry, and dehydration thickens the blood slightly. Drink water regularly throughout the flight.
  • Avoid alcohol and limit caffeine — both contribute to dehydration.
  • Wear loose, comfortable clothing — tight waistbands or clothing that restricts circulation isn't helpful.

Before You Travel

Before any long-haul flight in pregnancy, it is worth talking to your midwife or GP. They can:
  • Assess whether you have any additional risk factors for DVT (such as a previous clot, a clotting disorder, carrying twins, high BMI, or being over 35)
  • Advise whether you need low-molecular-weight heparin (a blood-thinning injection) — this is sometimes recommended for women with higher individual risk
  • Provide a fitness-to-fly letter, which some airlines require for pregnant passengers
  • Make sure there are no pregnancy complications that would make flying inadvisable

Check your airline's policy before booking. Most airlines allow travel up to 36 weeks for a single pregnancy and around 32 weeks for twins, but policies vary and you may need a letter from your midwife or GP confirming your due date and that you're fit to fly.

Knowing When to Get Help

Seek urgent medical attention if, during or after a flight, you notice:

  • Swelling, pain, redness, or warmth in one calf or leg (possible DVT)
  • Chest pain or difficulty breathing (possible pulmonary embolism — call 999 immediately)
  • Coughing up blood

DVT symptoms in pregnancy can overlap with normal pregnancy discomforts like leg swelling, so if you're at all unsure, call 111 and describe your symptoms. It's always better to be assessed.

Frequently Asked Questions

### Can I fly long-haul in the first trimester?

Yes, in most cases. If your pregnancy is uncomplicated and you feel well, there is no medical reason to avoid flying in the first trimester. Morning sickness can make flying uncomfortable, and it's worth having a plan for managing nausea on board. The heightened DVT precautions above apply from the first trimester onwards — pregnancy increases clot risk from very early on.

Do I need a fitness-to-fly letter?

Many airlines require a letter from your midwife or GP confirming your due date and that your pregnancy is uncomplicated once you are past a certain gestation (often around 28 weeks). Policies vary between airlines, so always check before you travel and get the letter in good time. Even if your airline doesn't require one, it can be reassuring to have your pregnancy reviewed before a long journey.

Is it safe to fly after 28 weeks?

For most uncomplicated singleton pregnancies, flying is considered safe up to around 36 weeks, though most airlines have their own cut-off. After 28 weeks, the risk of complications such as premature labour increases, and you want to make sure you are somewhere with appropriate maternity care if needed. Most airlines won't carry passengers beyond 36 weeks (or 32 weeks for twins). Talk to your midwife if you're planning to travel in the third trimester.

For personalised advice about flying during your pregnancy, including whether you need additional precautions, speak to your midwife or GP before you travel.

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