Pre-existing high blood pressure in pregnancy

High blood pressure often runs in families. Sometimes kidney or glandular disease may be responsible. However, eating too much salt, drinking too much alcohol, being overweight and not moving around enough each day can also contribute to high blood pressure and heart disease.

The effects of high blood pressure on your blood vessels are worsened by:

• cigarette smoking
• high levels of saturated fat in your diet
• high blood cholesterol.

Some medicines may cause raised blood pressure or make controlling it more difficult. These medicines include:

• the combined contraceptive pill
• non-steroidal anti-inflammatories (NSAIDs)
• some nasal drops and sprays
• some cough medicines, eye drops and appetite suppressants.

The main complication of having pre-existing hypertension in pregnancy is developing pre-eclampsia. Women with pre-existing hypertension have a higher chance (20%) of developing pre-eclampsia. This is why women with pre-existing hypertension need to be monitored closely during pregnancy.

Other complications include:

• stroke
• heart failure
• kidney failure
• premature delivery of your baby (before 37 weeks)
• poor growth of your baby
• placental abruption (severe bleeding from your placenta).

If you have pre-existing hypertension, you will usually be diagnosed before pregnancy or be on antihypertensive medications.

However, because high blood pressure doesn’t usually cause any symptoms, it may not be diagnosed until an antenatal visit (before 20 weeks) when you have your blood pressure checked. High blood pressure in pregnancy can be diagnosed if your blood pressure is consistently high in 2 occasions.

At each antenatal visit, your midwife or LMC will check your blood pressure and test your urine for protein. Your midwife will also check if you have any of the following symptoms:

• severe headache
• changes in eyesight such as seeing spots, flashing lights or floaters, blurry vision
• pain in your upper belly, tummy area or shoulder
• sudden and new swelling in your face, hands or eyes (some feet and ankle swelling is normal during pregnancy)
• sudden weight gain (more than 1 kg in a week or more than 3 kg in a month)
• vomiting later in your pregnancy (not the morning sickness of early pregnancy)
• difficulty breathing.

An increase in these are warning signs of pre-eclampsia. A sudden increase in blood pressure is often the first sign of a problem.

Women with pre-existing hypertension need to be closely monitored throughout the pregnancy. You will be taught the signs and symptoms of pre-eclampsia to watch out for as it is important to contact your midwife or GP if you develop any of these symptoms.

Treatment depends on how bad your blood pressure is and whether you have developed pre-eclampsia.

If you are taking medicines to treat high blood pressure before pregnancy and you are planning a pregnancy, speak to your doctor, nurse or midwife about reviewing your medication before you become pregnant. Your medication will be changed to one that is considered safe in pregnancy. 

If you are taking medicines to treat high blood pressure and you have just found out that you are pregnant, contact your doctor immediately so that your medication can be reviewed. 

Commonly prescribed antihypertensives in pregnancy

Commonly used blood pressure medicines (antihypertensives) during pregnancy include:

• labetalol
• nifedipine
• methyldopa.

When deciding whether or not to take antihypertensives during pregnancy, your doctor will discuss with you how necessary the medication is to your health against the possible risks to you or your baby, some of which will depend on how many weeks pregnant you are.

Additional medications

Because women with pre-existing hypertension have a higher chance of developing pre-eclampsia and other complications during pregnancy, you may also be given medicines to help prevent pre-eclampsia, such as:

• aspirin 100 milligrams orally once daily
• calcium 1.25 grams orally once daily
• a pregnancy multivitamin containing folic acid, eg, Elevit®.

Antihypertensive medications that are not safe during pregnancy

Examples of blood pressure medicines that should not be taken during pregnancy are:

• angiotensin-converting enzyme (ACE) inhibitors
  • Examples include captopril, cilazapril, enalapril, lisinopril, perindopril, quinapril
• angiotensin receptor blockers (ARBs)
  • Examples include candesartan, irbesartan, losartan
• water tablets (diuretics)
  • Examples include bendroflumethiazide, chlortalidone, indapamide, furosemide, hydrochlorothiazide, amiloride. 

Severe hypertension or if pre-eclampsia develops

If your blood pressure becomes severely high or you develop pre-eclampsia, you may be referred to an obstetrician or a specialist for treatment or monitoring and may need admission to hospital. You will need much closer supervision and will probably need to have your baby early.

The treatment and monitoring aim to keep you and your baby safe while your baby grows and develops as much as possible. If your baby does need to be delivered early there are treatments available to decrease the complications of being born prematurely.

Read more about pre-eclampsia.