Blood pressure in pregnancy classifier

The reading that has no symptoms

Blood pressure is measured at every single antenatal appointment, and there is a reason it is the one thing nobody skips. Raised blood pressure in pregnancy usually feels like nothing at all. By the time it produces symptoms, it has often been high for a while.

That is also why a number on a home monitor causes so much anxiety. You have a figure, you have no symptoms to compare it against, and the internet gives you either reassurance or terror depending on which page loads first. What follows is the actual set of lines NICE draws.

140/90, and why either number counts

Hypertension in pregnancy means 140 systolic or higher, or 90 diastolic or higher. Not both. A reading of 142/78 is hypertension. So is 128/94. People frequently reassure themselves that one number is fine, and the definition does not work that way.

One reading is not a diagnosis. Blood pressure moves with the time of day, with how long you have been sitting, with whether you rushed to the appointment, and with the cuff size. It also has a natural shape across pregnancy: it typically dips through the middle trimester and climbs back towards term. A series of readings tells you far more than any one of them.

160/110 is the number to act on

If there is one figure worth memorising from this page, it is this one. NICE NG201 lists a reading of 160/110 mmHg or more as requiring urgent action, and NG133 defines severe hypertension as anything over those numbers. At that level, contact your maternity unit the same day, whatever hour it is. Do not wait for the next appointment, and do not sit down for twenty minutes and re-measure until you get a number you prefer.

Three different conditions, not one

The word that decides everything is when.

Raised before 20 weeks, or present at booking, or already on medication: that is chronic hypertension. It means blood pressure that was there before the pregnancy, whether or not anyone had spotted it. It carries its own care: NICE offers aspirin from 12 weeks, treatment if sustained readings hit 140/90, and more frequent appointments.

New after 20 weeks with no significant protein: gestational hypertension. NICE expects a full assessment in a secondary care setting by someone trained in hypertensive disorders of pregnancy — a hospital appointment, not a note in your records.

New after 20 weeks plus protein or organ involvement: pre-eclampsia. This is the one everybody has heard of and the one this calculator will not tell you that you have, because the definition includes blood results and scan findings that no home monitor produces.

Why they keep testing your urine

The pot at every appointment is not a formality. Protein in the urine is what separates gestational hypertension from pre-eclampsia in the definitions, and it is the cheapest early signal there is.

A dipstick is a screening test, not a diagnosis. NICE says that if it reads 1+ or more, quantify it properly with an albumin:creatinine ratio, threshold 8 mg per mmol, or a protein:creatinine ratio, threshold 30 mg per mmol. It also says not to use a first morning sample and not to routinely collect urine for 24 hours, which used to be standard and is no longer recommended.

Symptoms that override the number entirely

NICE recommendation 1.1.1 lists symptoms that mean seeing a healthcare professional immediately, regardless of what any monitor says: 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.

The pain under the ribs is the one most often dismissed, usually as indigestion or as the baby kicking. It is worth taking seriously.

What treatment actually looks like

People hear "blood pressure medication in pregnancy" and assume it is a last resort. It is routine. NICE offers pharmacological treatment when blood pressure remains above 140/90, and to everyone with severe hypertension, with a target of 135/85 or less once treatment has started. Labetalol is usually first choice, with nifedipine or methyldopa as alternatives, and the choice takes account of any existing treatment, side effects and your own preference.

One thing NICE rules out explicitly is bed rest. It is not recommended as a treatment for gestational hypertension, and it has not been for years, despite being the first thing many people are told by a relative. Nor is salt restriction: NICE says do not recommend it during pregnancy solely to prevent gestational hypertension or pre-eclampsia.

Monitoring intensifies rather than the pregnancy simply continuing. In gestational hypertension that means blood pressure once or twice a week until it is 135/85 or less, dipstick testing alongside it, weekly bloods, an ultrasound at diagnosis and repeat scans if indicated. Planned early birth before 37 weeks is not offered where blood pressure is below 160/110 unless there is another medical reason.

Buying a monitor, if you are going to

NICE specifies a device validated for use in pregnancy, and this is not a formality either. Many consumer monitors have never been validated in pregnancy, and some read systematically low in pre-eclampsia — exactly the condition you would want them to catch. Check the model against a validation list before buying, use the right cuff size for your arm, and take the reading sitting, resting, with your arm supported at heart level.

What it means for next time

NICE publishes recurrence figures, and they are worth knowing rather than discovering. After pre-eclampsia, roughly 1 in 7 women have it again in a future pregnancy, rising to around 1 in 3 if the birth was between 28 and 34 weeks. After gestational hypertension, roughly 1 in 11. That is precisely why hypertensive disease in a previous pregnancy sits at the top of the high-risk list for aspirin next time.

This tool classifies one reading against a published table. It does not diagnose anything and does not replace assessment by a midwife or doctor.