Gestational hypertension: high blood pressure that starts in pregnancy

Blood pressure normally dips in the first half of pregnancy and rises again later. Doctors use particular labels depending on when high blood pressure starts. NICE Clinical Knowledge Summaries describe chronic hypertension as high blood pressure present before 20 weeks or before pregnancy, and gestational hypertension as new high blood pressure after 20 weeks without significant proteinuria.

The distinction matters because the advice and the level of surveillance differ. Someone with long-standing high blood pressure is at higher risk of pre-eclampsia and is usually referred for consultant-led care. Someone whose pressure first rises in the second half of pregnancy needs close monitoring to see whether it stays isolated or becomes pre-eclampsia, which the NHS describes as a problem with the placenta that can affect the kidneys, liver and brain.

For many women the blood pressure settles after the birth. Because the label is about timing rather than severity, the readings, symptoms and urine results are what guide care.

On its own, gestational hypertension rarely causes symptoms, which is why blood pressure and urine testing are routine. The symptoms that matter are those that suggest pre-eclampsia may be developing. The NHS lists a severe headache that does not go away with simple painkillers, vision problems such as blurred vision or flashing lights, pain below the ribs, sudden swelling of the face, hands or feet, feeling very unwell, heartburn that does not respond to medicine, and vomiting.

CKS adds epigastric pain and breathlessness to the list and says such symptoms warrant immediate medical review, including during the first four weeks after birth. The NHS notes that pre-eclampsia can sometimes develop in the days or weeks after the baby is born.

• If you are pregnant and have any of these symptoms, call your maternity unit if you have the number; if you cannot reach them or have recently given birth, call NHS 111, and call 999 if you feel seriously unwell or have a seizure.

• Do not wait for your next scheduled appointment, even if your last blood pressure reading was normal.

It is not fully understood why blood pressure rises in some pregnancies. For pre-eclampsia, which is closely related, the NHS lists higher risk in people with diabetes, pre-existing high blood pressure, kidney disease or an autoimmune condition, those who had pre-eclampsia before, and in a first pregnancy, being 40 or over, a Black or South Asian ethnic background, a multiple pregnancy, a close relative with pre-eclampsia, a gap of 10 years or more since the last pregnancy, or a BMI of 35 or more before pregnancy.

At your first antenatal appointment the midwife will review these factors. If you are assessed as higher risk, the NHS says you may be advised to take low-dose aspirin daily from week 12 of pregnancy until birth, and calcium supplements if you do not get enough from your diet. You should not start either unless a midwife or doctor has advised it.

Your midwife or doctor will measure blood pressure and test your urine for protein at every antenatal appointment. If a high reading is found, the NHS says you will be assessed in hospital by a healthcare professional, usually a midwife. Blood pressure may be checked more often, you may not always need treatment, and further tests can include blood tests and ultrasound scans to check your baby's growth.

After 20 weeks, the NHS says you may be offered a PLGF (placental growth factor) blood test to help rule out pre-eclampsia. CKS defines significant proteinuria as a urinary protein to creatinine ratio of at least 30 mg/mmol, and a dipstick result of 1+ or more prompts one of these more precise tests.

Mild gestational hypertension may need monitoring but not medicine. The NHS says severe hypertension requires treatment until the reading falls below 160/110 mmHg. CKS lists labetalol, nifedipine and methyldopa among medicines used in pregnancy. If you already take blood pressure medicines before conception, the NHS says to speak to your GP or specialist, because some medicines are not safe in pregnancy and may need to be changed.

Your doctor may discuss the timing of the birth with you. The NHS says that if you take blood pressure medicine you should continue it in labour, that blood pressure is monitored hourly in labour, and that as long as it stays within target it should not stop a vaginal birth. If you have severe hypertension, monitoring is every 15 to 30 minutes and forceps, ventouse or caesarean section may be recommended.

The NHS says pre-eclampsia has no cure but symptoms usually improve after the baby is born, and that it is often safer for the baby to be born early, in some cases before 37 weeks. Hypertension medicines can pass into breast milk, but most lead to very low levels and the NHS says you should be able to breastfeed.

If you are still taking medicine after the birth, the NHS says you should be offered an appointment with a doctor about 2 weeks after transferring to community midwife care, to check whether treatment needs to change or stop. Everyone with hypertension in pregnancy should be offered a review at 6 to 8 weeks to check blood pressure.

CKS stresses that postpartum monitoring and follow-up are essential for all women who have had a hypertensive disorder of pregnancy. It is sensible to tell your GP about the pregnancy so that it is recorded in your health record and can be taken into account at later blood pressure checks.

Blood pressure checks are part of routine NHS antenatal care, and a raised reading leads to assessment in hospital, usually by a midwife, as the NHS describes. Hospital birth, monitoring and postnatal follow-up are all included.

Some people choose private antenatal care or an obstetrician-led package, often for continuity with one consultant. In practice the same tests and thresholds apply, and anyone who develops hypertension is still likely to be managed at a unit able to provide neonatal and emergency care. If you use private care, ask who you should contact out of hours and which hospital would admit you.