Low blood pressure in the third trimester: what to know

Pregnancy changes blood vessels and circulation. Later in pregnancy, lying flat on your back may also make some people feel faint because the growing uterus can affect major blood vessels. Heat, dehydration, long periods standing, missed meals and anaemia can add to light-headedness. A low reading matters most when it comes with symptoms or a change from your usual pattern.

Dizziness is common in pregnancy but should not be dismissed when it is severe or recurring. Your midwife, obstetric team or GP can check blood pressure, urine, blood count, medicines and other causes.

Sit down as soon as you feel faint, or lie on your side rather than flat on your back. Drink fluids regularly, eat small balanced meals, rise slowly and avoid very hot rooms or standing still for long periods. Comfortable support stockings may help some people, but ask your maternity team before using them. Do not increase salt, take supplements or change medicines without advice.

Keep a note of readings, symptoms, meals, fluid intake and the baby's usual movement pattern. A GP Consultation can help when symptoms persist or your maternity team asks for a general medical review.

Contact maternity services urgently for fainting, vaginal bleeding, severe abdominal pain, severe headache, vision changes, sudden swelling, chest pain, breathlessness, confusion, or reduced or changed baby movements. Emergency help is needed for collapse, heavy bleeding, severe breathing difficulty or a serious injury from a fall.

Ask what blood-pressure readings concern them, whether you need checks for anaemia or dehydration, which position is safest for rest, and where to call outside appointments. Tell them about every medicine, supplement and episode of faintness.