Preeclampsia screening: how blood pressure is checked in pregnancy

What preeclampsia is

Preeclampsia is high blood pressure with signs of liver or kidney damage that starts after the 20th week of pregnancy. It occurs in 3% to 7% of pregnancies, and people who have it often do not feel sick. (MedlinePlus) It often develops in the third trimester; when it starts before 34 weeks it is called early-onset preeclampsia. It can also develop in the weeks after childbirth. (ACOG) Because you are unlikely to notice the early signs, blood pressure and urine are checked at routine visits. (NHS)

• Chronic high blood pressure: present before pregnancy or found in the first 20 weeks.
• Gestational high blood pressure: new high blood pressure after the 20th week in someone whose blood pressure was normal before.
• Preeclampsia: new high blood pressure, most often after the 20th week, with protein in the urine or any of these: low platelets, liver problems, kidney problems, fluid in the lungs, a new headache that medicine does not help, or vision problems. (USPSTF, 2023)

The blood pressure check

Your ob-gyn should check your blood pressure at each prenatal visit. Blood pressure changes often during the day, so if one reading is high, another may be taken later in the same visit. (ACOG) An accurate reading needs the right technique, a device checked for use in pregnancy and a cuff that fits your arm. (USPSTF, 2023) In a trial that added home readings to the office checks, preeclampsia and related disorders were not found sooner. (USPSTF, 2023)

The numbers used in pregnancy

The top number is the pressure when the heart beats; the bottom number is the pressure when it relaxes between beats. (ACOG) Both are in mm Hg.

Outside pregnancy, readings are sorted into different groups: blood pressure readings and what they mean. Someone who had low blood pressure early in pregnancy and then a large rise needs close watching for other signs of preeclampsia, even below these numbers. (MedlinePlus)

Urine and blood checks

A high reading may be the first sign of preeclampsia. If it is high, it may be checked again, and you may have a urine test for protein and blood tests of your liver, your kidneys and your platelets. (ACOG) The USPSTF says urine dipstick tests have low accuracy for protein in pregnancy and that protein alone may not predict how preeclampsia will go, so it does not support routine dipstick tests for screening. Measuring urine protein is still part of how preeclampsia is diagnosed. (USPSTF, 2023)

In the UK, NICE says that if a dipstick shows protein (1+ or more), a protein:creatinine or albumin:creatinine ratio is used to measure it. (NICE NG133) NICE defines preeclampsia as new high blood pressure after 20 weeks with one or more new findings, including these:

NICE also counts seizures, severe headaches, vision problems and signs that the baby is not growing well. US labs may report urine protein in other units; compare your result with the range on your own report. (NICE NG133) If preeclampsia is suspected between 20 weeks and 36 weeks and 6 days, NICE offers a placental growth factor (PLGF) based blood test to help rule it out. (NICE NG133) What the usual tests report: urinalysis results, complete blood count (platelets) and metabolic panel (creatinine and liver enzymes).

Severe features, per ACOG: a low platelet count, abnormal kidney or liver function, pain in the upper belly, changes in vision, fluid in the lungs, a severe headache, or a top number of 160 or higher or a bottom number of 110 or higher. (ACOG) Your doctor decides what your result means for you.

Warning signs: call the same day

ACOG lists these symptoms and says to call your ob-gyn right away if you have any of them, especially in the second half of pregnancy: (ACOG)

• swelling of the face or hands
• a headache that will not go away
• seeing spots or changes in eyesight
• pain in the upper belly or shoulder
• nausea and vomiting in the second half of pregnancy
• sudden weight gain
• trouble breathing

NICE's list is similar: a severe headache, blurring or flashing before the eyes, severe pain just below the ribs, vomiting, and sudden swelling of the face, hands or feet. It advises seeing a healthcare professional immediately. (NICE NG133) Some swelling of the feet and ankles is normal in pregnancy. (MedlinePlus)

After the birth

• Preeclampsia can start after delivery, most often within 48 hours. Blood pressure sometimes gets worse in the first few days, and the risk lasts up to 6 weeks. Contact your provider if you notice symptoms after delivery. (MedlinePlus)
• The USPSTF found little evidence on screening after birth. It suggests that patients learn the warning signs before leaving the hospital, and that those with a high blood pressure disorder have later blood pressure checks. (USPSTF, 2023)
• Later in life, people who had preeclampsia have a higher risk of kidney disease, heart attack, stroke and high blood pressure, and of preeclampsia in a future pregnancy. (ACOG) NICE puts the chance of a high blood pressure disorder in a future pregnancy at about 1 in 5. (NICE NG133) The heart checks to keep up with: heart screenings by age.

Where they differ:

• Urine at every visit: the USPSTF does not support routine urine dipstick tests to screen for preeclampsia. NICE recommends checking urine for protein at each antenatal visit, and ACOG recommends a first (baseline) urine protein test, as the USPSTF summarizes them. (USPSTF, 2023)
• Blood pressure after the birth: ACOG advises a blood pressure check no later than 7 to 10 days after the birth for anyone with a high blood pressure disorder of pregnancy, and within 72 hours for severe high blood pressure, as the USPSTF summarizes it. (USPSTF, 2023) For gestational high blood pressure, NICE measures it daily for the first 2 days and at least once between day 3 and day 5. (NICE NG133)
• PLGF blood test: NICE offers it when preeclampsia is suspected; it is not part of the USPSTF recommendation, which is blood pressure measurement. (NICE NG133) (USPSTF, 2023)

Who is at higher risk

ACOG's high-risk list includes preeclampsia in a past pregnancy, twins or more, chronic high blood pressure, kidney disease, diabetes, autoimmune conditions such as lupus, or several moderate risk factors. Moderate risk factors include a first pregnancy, a pregnancy more than 10 years after the last one, a BMI over 30, a mother or sister who had preeclampsia, and being 35 or older. (ACOG) If you are at higher risk, your prenatal care team may talk with you about prevention. What the USPSTF recommends, and when: pregnancy screenings by week. Do not start any medicine on your own.

This page does not give diagnosis, medicine or treatment advice. The other prenatal tests: pregnancy screenings by week. Blood pressure checks are on the USPSTF list of recommended (A and B) services. (USPSTF A and B list)

Questions people ask

How is preeclampsia screened for?

With a blood pressure check at every prenatal visit, all through pregnancy. The USPSTF recommends this for all pregnant people (grade B, 2023). If a reading is high, it is checked again, and a urine test for protein and blood tests may follow. (USPSTF, 2023) (ACOG)

What blood pressure is too high in pregnancy?

A top number of 140 or higher, or a bottom number of 90 or higher, measured twice at least 4 hours apart, is a positive screen. A top number of 160 or higher, or a bottom number of 110 or higher, is in the severe range. (USPSTF, 2023) (ACOG)

Do I need a urine dipstick at every visit?

Groups differ. The USPSTF says the evidence does not support routine urine dipstick tests to screen for preeclampsia, because they are not very accurate in pregnancy. NICE in the UK checks urine for protein at each antenatal visit, and ACOG advises a first urine protein test, as the USPSTF summarizes them. (USPSTF, 2023)

Can preeclampsia happen after the baby is born?

Yes. It can start after delivery, most often within 48 hours, and the risk lasts up to 6 weeks. Contact your provider if you notice symptoms after delivery. (MedlinePlus)

Which symptoms need a call right away?

ACOG lists swelling of the face or hands, a headache that will not go away, seeing spots or changes in eyesight, pain in the upper belly or shoulder, nausea and vomiting in the second half of pregnancy, sudden weight gain and trouble breathing. If you have any of them, call your ob-gyn right away. (ACOG)

Related

• Pregnancy screenings by week
• Gestational diabetes glucose test results
• Blood pressure readings and what they mean
• Blood pressure screening: who needs it and how often
• Urinalysis results
• Heart screenings by age