Why is high blood pressure dangerous in pregnancy?

Blood pressure of 140/90 or higher, especially after 20 weeks, can be a sign of preeclampsia (with protein in urine and swelling); it impairs blood flow to the fetus and is dangerous for the mother. Readings of 160/110 or higher are an emergency — see a doctor urgently or call emergency services.

Is low blood pressure in pregnancy dangerous?

Moderately low blood pressure in the first trimester is common and less dangerous than high, but it causes weakness, dizziness and fainting and worsens toxicosis. Fainting (fall risk) and sharp weakness are concerning — with them, see a doctor to rule out other causes.

How do I measure blood pressure correctly in pregnancy?

Measure at rest seated, after 5 minutes' rest, arm at heart level, not right after eating, coffee or exertion. With high readings, re-measure after a few minutes. In the second half of pregnancy it helps to keep a blood pressure diary and show it to your doctor at visits.

Blood pressure 140 in pregnancy — what should I do?

A one-off 140/90 can be a fluke (stress, poor measurement) — re-measure at rest. But persistent 140/90 or higher, especially after 20 weeks or with headache, swelling or spots, is a reason to see a doctor urgently: it can be preeclampsia, which matters to catch early.

Blood Pressure in Pregnancy: Norms, High and Low Readings

PregnancyJune 28, 2026

Reviewed by the LabReadAI medical team

Blood Pressure in Pregnancy: Norms, High and Low Readings

Monitoring blood pressure is one of the main points of pregnancy care: both high and low pressure matter. Let's break down what blood pressure is normal in pregnancy, why deviations are dangerous and when to see a doctor urgently.

Normal Blood Pressure in Pregnancy

The norm is roughly as before pregnancy, usually below 140/90. In the first half, blood pressure often dips a little (hormones and vessel dilation), returning to baseline by the third trimester. It is important to know your "usual" blood pressure and measure regularly.

High Blood Pressure: Why It Is Dangerous

Blood pressure ≥140/90, especially after 20 weeks, is a warning: it can be a sign of preeclampsia (with protein in urine and swelling — see preeclampsia). High blood pressure impairs blood flow to the fetus and is dangerous for the mother. Readings ≥160/110 are an emergency.

Low Blood Pressure: Why and What It Threatens

In the first trimester, a frequent drop in blood pressure causes weakness, dizziness, fainting and worsens toxicosis — see toxicosis in pregnancy. Moderately low blood pressure is less dangerous than high, but fainting risks a fall; sharp weakness warrants seeing a doctor.

How to Measure Blood Pressure Correctly

at rest, seated, after 5 minutes' rest, arm at heart level;
not right after eating, coffee or exertion;
with high readings, re-measure after a few minutes;
keep a blood pressure diary, especially in the second half.

When to See a Doctor Urgently

Immediately: blood pressure 160/110 or higher; 140/90+ with headache, face/hand swelling, vision changes, pain under the right ribs (possible preeclampsia); fainting. Blood pressure is assessed with protein in urine and tests — what tests are done in pregnancy.

To understand your readings and tests in plain language, upload the form (PDF or photo) to the lab results interpretation service. This helps you understand the result, but with alarming readings see a doctor at once.

This article is informational. Diagnosis and treatment in pregnancy are the doctor's job.

Frequently asked questions

Roughly as before pregnancy, usually below 140/90. In the first half it often dips a little, returning to baseline by the third trimester. It is important to know your 'usual' blood pressure and measure regularly — deviations are assessed against your norm and the stage of pregnancy.
Blood pressure of 140/90 or higher, especially after 20 weeks, can be a sign of preeclampsia (with protein in urine and swelling); it impairs blood flow to the fetus and is dangerous for the mother. Readings of 160/110 or higher are an emergency — see a doctor urgently or call emergency services.
Moderately low blood pressure in the first trimester is common and less dangerous than high, but it causes weakness, dizziness and fainting and worsens toxicosis. Fainting (fall risk) and sharp weakness are concerning — with them, see a doctor to rule out other causes.
Measure at rest seated, after 5 minutes' rest, arm at heart level, not right after eating, coffee or exertion. With high readings, re-measure after a few minutes. In the second half of pregnancy it helps to keep a blood pressure diary and show it to your doctor at visits.
A one-off 140/90 can be a fluke (stress, poor measurement) — re-measure at rest. But persistent 140/90 or higher, especially after 20 weeks or with headache, swelling or spots, is a reason to see a doctor urgently: it can be preeclampsia, which matters to catch early.

#Preeclampsia #Swelling in Pregnancy #Pregnancy Tests #Toxicosis in Pregnancy

For informational purposes only

This article is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Please consult a healthcare professional for medical guidance.

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