Is flying safe during pregnancy?

The verdict

Yes, if your pregnancy is straightforward. This is one of the few pregnancy questions where a royal college has published a dedicated leaflet, and the leaflet is unambiguous.

The Royal College of Obstetricians and Gynaecologists states that occasional air travel during pregnancy is not harmful for you or your baby as long as you are having an uncomplicated pregnancy. It adds that there is no evidence that the changes in air pressure or the decrease in humidity have a harmful effect, and no evidence that flying will cause miscarriage, early labour or your waters to break. The NHS puts it in one line: flying is not harmful to you or your baby.

What changes as pregnancy advances is not the aircraft. It is the chance that you go into labour a long way from a maternity unit. That is why every limit you will read on this subject is a date rather than a dose.

Why the cabin is not the risk

Three things about flying worry people, and two of them have been answered directly.

Cabin pressure. ACOG states that lower air pressure during a flight may slightly reduce the amount of oxygen in your blood, but your body will adjust. The RCOG finds no evidence that pressure or humidity changes cause harm in an uncomplicated pregnancy.

Radiation. Anyone who flies is exposed to a slight increase in cosmic radiation. The RCOG says occasional flights are not considered to present a risk to you or your baby. ACOG says exposure increases at higher altitudes but the level is not a concern for occasional travel. Both attach the same exception: if you are a member of flight crew or you fly frequently as part of your work, the question becomes one of cumulative dose, and the RCOG tells you to take it to your occupational health department rather than to a leaflet.

Blood clots. This is the one that is real. Pregnancy raises your risk of deep vein thrombosis, and so does sitting still. The RCOG states that you have a higher risk of DVT when pregnant and for up to six weeks after birth than a woman who is not pregnant, that flying increases the risk further because of prolonged sitting, and that the risk rises with the length of the flight. ACOG puts a number on the travel component: research shows that any type of travel lasting four hours or more, whether by car, train, bus or plane, doubles the risk of DVT.

What to do on a flight over four hours

The RCOG says that on a short haul flight of less than four hours it is unlikely you will need any special measures. For medium and long haul flights over four hours it lists what to do: wear loose clothing and comfortable shoes, try to get an aisle seat and take regular walks around the plane, do in-seat exercises every 30 minutes or so, drink water at regular intervals, cut down on caffeinated drinks, and wear graduated elastic compression stockings. It is specific that these are not the same as standard flight socks and that your midwife or doctor needs to provide the correct size and type.

Two further points from the same leaflet are worth knowing. If you have other risk factors for DVT you may be advised to have heparin injections on the day of the flight and daily for a few days afterwards, and you will need a doctor's letter to carry them through security. And low-dose aspirin does not appear to reduce the risk of a DVT, although you should keep taking it if it was prescribed for another reason.

How late you can actually fly

Two different limits apply and people confuse them constantly. The clinical limit comes from the RCOG. The commercial limit comes from your airline, and it is the one that will actually stop you at the gate.

The RCOG says the safest time to fly is before 37 weeks if you are carrying one baby, and before 32 weeks with an uncomplicated twin pregnancy. The NHS gives the same figures, framed as the point at which the chance of going into labour naturally rises.

Airline policies, all read on 9 August 2026, differ more than most people expect:

• British Airways does not carry you after the end of the 36th week with one baby, or the end of the 32nd with more than one.
• easyJet stops at the end of the 35th week for a single pregnancy and the end of the 32nd for a multiple one, and asks for no medical certificate at all.
• Qantas splits its rule by flight length. On flights of four hours or more it is the end of the 36th week, or the 32nd for twins. On flights under four hours it is the end of the 40th week, or the 36th for twins.

ACOG's summary for the United States is that most airlines allow you to fly inside the country until about 36 weeks, and that the cut-off for an international flight may be earlier. Qantas attaches a caveat that every traveller should read: it does not represent that travel is safe at any particular point in your pregnancy, and the periods it publishes are only its minimum requirements.

The paperwork from 28 weeks

The NHS warns that after week 28 the airline may ask for a letter from your doctor or midwife confirming your due date and that you are not at risk of complications, that you may have to pay for it, and that you may wait several weeks to get it. British Airways requires its own pregnancy form or an official letter, completed and stamped by a doctor or midwife, from week 28, and states that travelling earlier than 28 weeks needs no paperwork. Qantas also requires a certificate after 28 weeks, confirming the estimated date of delivery, whether the pregnancy is single or multiple, and that it is routine.

When you may be advised not to fly

The RCOG lists the situations in which you may be told not to fly: you are at increased risk of going into labour before your due date, you have severe anaemia, you have sickle cell disease and have recently had a crisis, you have recently had significant vaginal bleeding, or you have a serious lung or heart condition that makes breathing very difficult. ACOG adds preeclampsia, prelabour rupture of membranes and preterm labour to the list of complications for which travel is not recommended.

Both make the same underlying point about timing. The RCOG notes that most obstetric emergencies happen in the first and third trimesters, which is why mid-pregnancy is the standard recommendation. ACOG names that window as 14 to 28 weeks; the NHS describes it as between four and six months.

Where guidance genuinely differs

The UK sets 37 weeks, the US works to about 36. The RCOG and the NHS both use 37 weeks for a single pregnancy. ACOG describes the practical US position as most airlines allowing domestic flights until about 36 weeks. The gap is one week and it is commercial rather than clinical.

Cruise operators are far stricter than airlines. ACOG states that many cruise ships only allow you to travel until about 23 weeks. The NHS notes that ferry companies often refuse carriage beyond 32 weeks on standard crossings and 28 weeks on high-speed ones. If you are combining a flight with a sailing, the boat is usually the binding constraint.

The destination can matter more than the flight. The CDC's Yellow Book advises pregnant travellers to avoid destinations with a risk of Zika or malaria altogether, and the NHS says it is not recommended to travel to parts of the world where Zika is present. No airline cut-off addresses that, and it is the part of the decision that a due-date calculator cannot make for you.