Dizziness and Fainting During Pregnancy

Why pregnancy makes you lightheaded

The mechanism is circulatory. Pregnancy, Birth and Baby explains that "when you're pregnant, blood vessels expand. This helps increase blood flow to your baby. There are also many hormonal changes that affect your circulatory system." Blood pressure falls through the first trimester, continues to fall in the second, then rises back towards pre-pregnancy levels by the end.

The HSE lists four causes in plain terms:

• Hormone changes — "this can cause your blood pressure to drop and less blood to get to your brain".
• Overheating.
• Low blood sugar — "keep a snack with you and avoid skipping meals".
• Low iron levels.

There is also a positional cause. From the second trimester onwards, lying on your back puts extra pressure on a major blood vessel returning blood to the heart, which reduces the blood reaching your brain. That is why lightheadedness while lying flat is a recognised pregnancy phenomenon rather than something odd.

Pregnancy, Birth and Baby adds the blood-volume side: because there is more blood circulating, "you can sometimes feel dizzy, especially when you change positions from lying to standing."

What is normal

• Feeling lightheaded when you stand up quickly from sitting or lying.
• Feeling faint after standing still for a long time — in a queue, on public transport.
• Feeling hot, sweaty and dizzy in a warm room or a hot bath.
• Lightheadedness when you have gone too long without eating.
• Feeling faint while lying on your back in the second half of pregnancy.

What to do in the moment

The NHS gives specific, practical instructions:

• Get up slowly after sitting or lying down.
• If you feel faint while standing, find a seat quickly. The faintness should pass — "if it does not, lie down on your side".
• If you feel faint while lying on your back, turn onto your side.

If someone else faints while pregnant, the HSE advises rolling them onto their left side with the left knee pulled up towards the chest — the point being to take the weight of the womb off the major blood vessel returning blood to the heart.

Sleeping position, stated accurately

This is widely garbled online, so it is worth being precise. The NHS advises avoiding going to sleep on your back after 28 weeks, because it has been linked to a higher risk of stillbirth. Tommy's Sleep On Side campaign reports that the risk of stillbirth is doubled if women go to sleep on their backs in the third trimester, and that this applies to every episode of sleep — night, naps, and returning to sleep after waking.

But the common claim that the left side is safer is not supported. Tommy's states plainly: "The MiNESS study did not find a difference in risk between sleeping on the right or left side." Either side is fine. And if you wake up on your back, Tommy's advises not to be concerned — simply roll back onto your side.

What is not just pregnancy dizziness

Dizziness on its own is usually benign. Dizziness in combination is what changes the picture.

With bleeding or one-sided tummy pain: possible ectopic pregnancy

Pregnancy, Birth and Baby is direct: "If you're in early pregnancy and you faint, feel dizzy, or have bleeding or abdominal pain, this could be a sign of an ectopic pregnancy... Go straight to your nearest emergency department." The NHS lists feeling very dizzy or fainting alongside sharp sudden intense tummy pain and feeling sick as signs of a ruptured ectopic pregnancy requiring an ambulance.

With headache or vision changes: possible pre-eclampsia

The RCOG's warning list is the fullest available:

• "a severe headache that doesn't go away with simple painkillers"
• "problems with your eyesight, such as blurred vision or flashing lights in front of your eyes"
• "severe pain just below your ribs"
• "heartburn that doesn't go away with antacids"
• "rapidly increasing swelling of your face, hands or feet"
• nausea and vomiting; feeling very unwell

The RCOG's instruction: "These symptoms can be serious and you should seek medical help immediately if you develop any of them." Note that the RCOG also says pre-eclampsia often causes no symptoms at all and may be diagnosed for the first time at a routine antenatal appointment — which is a good argument for not skipping them. It usually appears towards the end of pregnancy, but can also appear for the first time after birth.

The HSE draws a useful gradient specifically for dizziness: a mild headache or slightly blurry vision with dizziness means contacting your doctor or midwife; a severe headache means urgent contact.

With anaemia

Low iron is a common and treatable cause. If dizziness comes with tiredness, breathlessness, palpitations or unusual paleness, ask for a blood test rather than assuming it is normal pregnancy tiredness.

When to call someone

Call your local emergency number (999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, or 111 in New Zealand) or go to an emergency department if dizziness or fainting comes with:

• Vaginal bleeding or severe tummy pain, especially on one side.
• Pain in the tip of your shoulder.
• Chest pain or an irregular heartbeat.
• A severe headache, or visual disturbance such as flashing lights.
• Loss of consciousness lasting more than a few minutes, or a head injury from the fall.

Contact your midwife or doctor the same day if:

• This is the first time you have fainted, or you have fainted more than once.
• You hit your head when you fainted.
• Dizziness is severe and does not go away.
• You have a mild headache or slightly blurry vision alongside the dizziness — the HSE names both specifically.

What actually helps

• Change position slowly, particularly getting out of bed.
• Eat regularly and keep a snack with you. The HSE names skipping meals as a direct cause.
• Drink enough. Pregnancy, Birth and Baby advises drinking plenty of water.
• Avoid getting overheated — hot baths, hot rooms, standing in the sun.
• Lie on your side rather than your back from the second trimester.
• Get your iron checked if dizziness is recurrent.

On driving, be aware that no national health guidance we could verify sets a rule about driving after fainting in pregnancy — but your licensing authority's medical rules do apply, and they differ by country. If you have fainted without warning, raise it with your midwife or doctor before driving again rather than assuming it is fine.