Call your maternity unit now

The NHS puts sudden vision problems on its list of pregnancy symptoms you need to get help for, and its wording leaves no room for interpretation: "Vision problems that start in pregnancy, such as blurring or seeing flashing lights, can sometimes be a symptom of pre-eclampsia. This needs to be checked immediately."

The NHS swelling page repeats it in its urgent-advice box: call your midwife, GP or labour ward immediately if you have problems with your vision, such as blurring or flashing lights in your eyes, and lists the symptoms that commonly travel with it:

a sudden increase in swelling in your face, hands or feet
a very bad headache
severe pain just below your ribs
heartburn that does not go away when you take antacid medicine
feeling very unwell
feeling sick and being sick

The HSE frames the same cluster from the other end: contact your midwife, GP or obstetrician immediately if you have "a severe headache — especially with other symptoms including blurred vision, upper stomach pain, nausea or swelling".

Tommy's is briefer and covers all versions: "If you have vision problems, always tell your midwife or doctor (GP) straight away, so they can check it out."

Which number

The NHS sets out who to contact by stage: your GP surgery or an early pregnancy unit in the first 12 weeks; your midwife or an early pregnancy unit from 12 to 19 weeks; your midwife or maternity unit from 20 weeks. Pre-eclampsia usually starts after 20 weeks, so for most people this is a call to the maternity unit. Call 999 if you think it is life-threatening.

Why vision is a pre-eclampsia symptom at all

Pre-eclampsia is a disorder of blood pressure and blood vessels, and the retina and the brain are both organs where raised pressure shows itself early. That is why visual disturbance sits on the same list as a severe headache and pain under the ribs: they are three windows onto the same process.

RCOG's patient information includes severe headache, problems with vision such as blurring or flashing before the eyes, severe pain just below the ribs, vomiting and sudden swelling of the face, hands or feet among the symptoms that should prompt urgent contact. NICE's guideline on hypertension in pregnancy (NG133) builds assessment around blood pressure and urine protein testing, which is why the first two things that will happen when you ring are a blood pressure reading and a urine dip.

The NHS notes that pre-eclampsia often produces no symptoms at all in its early stages and is picked up at routine antenatal appointments. When symptoms do appear, they are the ones above, and they mean the process is already established.

What it can feel like

People describe it in various ways, and none of them are more or less serious than the others:

blurring, as if you need to blink something away that will not clear
flashing lights, sparks or zigzags at the edge of vision
spots or floaters that are new
a patch of vision that has gone dark or absent
double vision
light hurting more than usual

Tommy's notes that pre-eclampsia "can cause vision loss", which is the reason the guidance is worded as immediately rather than soon.

The milder causes — read these after you have rung

Tommy's is the most useful source here because it covers the ordinary explanations without softening the urgent one. It notes that most eye problems or vision changes in pregnancy resolve themselves soon after birth, and that you might even need a stronger prescription because eyesight can change so much in pregnancy.

Dry eye. Tommy's says dry eye syndrome is thought to be more likely in pregnancy, possibly because of hormones or temporary changes to the eyes. It causes dryness and burning, "some people describe it as like having grit under their eyelids", and less commonly blurred vision. Treatment is usually eye drops from a GP or optometrist.
Ocular hypertension. Slightly raised pressure in the eyes, which Tommy's says affects some pregnant people and is often picked up at a routine eye check. Symptoms, when present, include blurred vision, headaches and eye pain. It means more frequent check-ups to make sure it does not progress to glaucoma.
Migraine. Tommy's says most people get fewer migraines in pregnancy but some find them worse, and some have a first attack while pregnant. The visual symptoms it lists are blind spots in one eye, or an aura such as flashing lights before the headache starts. It advises telling your GP even if you have had migraines before, because some migraine medicines are not recommended in pregnancy.
Diabetes. The NHS lists blurred eyesight among the symptoms that can appear if blood sugar levels get too high, alongside increased thirst, needing to pee more often, a dry mouth, tiredness and genital itching or thrush. Tommy's notes that anyone with diabetes should have eye screening and extra hospital appointments in pregnancy.

The order that matters

Every one of the mild causes above is more likely than pre-eclampsia. That is not a reason to work through them first. Blood pressure and a urine sample take ten minutes and rule out the one that matters; dry eye and a new spectacle prescription will still be there afterwards.

The NHS instruction elsewhere on its red-flag pages applies here too: do not wait until the next day, even if it is the middle of the night.

Blurred Vision in Pregnancy