Chronic hypertension in pregnancy: planning, aspirin, monitoring and the postnatal period

Blood pressure that is high before conception, or already high in early pregnancy, is described as chronic hypertension. Its causes include essential hypertension, kidney disease and, less often, hormonal conditions. By contrast, gestational hypertension appears later in pregnancy and usually settles after birth, while pre-eclampsia combines high blood pressure with effects on other organs such as the kidneys or liver.

The NHS lists existing high blood pressure as a risk factor for pre-eclampsia, which is why women with chronic hypertension are checked more closely.

The ideal time to talk is before pregnancy. Some blood pressure medicines are not suitable in pregnancy, and others are safer. Tell your GP if you are planning a pregnancy, and tell your midwife at booking exactly what you take. Never stop or switch tablets yourself; your doctor will balance control of your blood pressure against safety for the baby.

At booking, a baseline is recorded and you will be assessed for other risks such as diabetes, kidney disease or a family history of pre-eclampsia.

The RCOG lists high blood pressure before pregnancy as a high-risk factor, and women in this group are advised to take low-dose aspirin of 75 to 150 mg daily from 12 weeks until 36 weeks. Tommy's notes that the evidence shows it slightly reduces the risk of pre-eclampsia and its complications. The NHS adds that you should not start aspirin or calcium supplements unless a midwife or GP has told you to.

Expect closer surveillance than in a routine pregnancy. The midwife or doctor will measure blood pressure and test your urine for protein at antenatal visits, and you may have blood tests for kidney and liver function. Ultrasound scans check the baby's growth and the amount of amniotic fluid, and the RCOG says scans are offered at least every 2 weeks when pre-eclampsia raises concern. Some women also measure blood pressure at home.

• A severe headache that does not go away with simple painkillers.

• Problems with vision, such as flashing lights or blurring.

• Pain just below the ribs, or persistent heartburn.

• Sudden swelling of the face, hands or feet.

• Vomiting or feeling generally unwell.

The RCOG recommends birth at 37 weeks or earlier if complications develop. Induction or caesarean section is chosen according to your blood pressure control, the baby's growth and your own wishes. The NHS says that in some cases it is safer for the baby to be born before 37 weeks. During labour your blood pressure is monitored closely.

Blood pressure often changes after birth, sometimes rising a few days later, so monitoring continues and medicines may be adjusted. Your healthcare team should ensure that the medicines are safe to use while breastfeeding. Tommy's describes a GP appointment 2 weeks after transfer from hospital care and another 6 to 8 weeks after the birth.

Women who have had pre-eclampsia have a higher long-term chance of high blood pressure, stroke and heart disease, so keep up regular blood pressure checks and healthy habits.