High blood pressure in pregnancy

A baby receives all its food and oxygen from the mother's blood through the placenta. This means that your heart has to work harder to send blood to the placenta and then to your baby.

The placenta usually has large blood vessels that make it easy for the food to get to your baby. Because these blood vessels are so big, your blood pressure normally drops during the middle trimester of your pregnancy (14 to 28 weeks) and returns to normal by the end of the pregnancy.
 

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If your blood pressure is too high during pregnancy, it can affect the way your placenta develops and works. The blood vessels in the placenta may not have developed normally and the blood flow to your baby can be affected. This is a risk to you and your baby, and it can be a sign of a serious complication known as pre-eclampsia.

When to get help 

If you have any of the following symptoms contact your midwife or lead maternity carer (LMC) straight away. These could be warning signs of pre-eclampsia:

• ongoing, persistent or severe headache
• changes in eyesight such as seeing spots, flashing lights or floaters or 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)
• passing only small amounts or urine (wee)
• sudden weight gain (more than 1 kg in a week or more than 3 kg in a month)
• nausea or vomiting later in your pregnancy (not the morning sickness of early pregnancy)
• difficulty breathing or feeling short of breath.

Blood pressure is shown as 2 numbers:

• The top number (systolic) is the highest pressure in your arteries when your heart pumps blood to the rest of your body.
• The bottom number (diastolic) is the lowest pressure when your heart rests between heartbeats.

Blood pressure is normally written as the top number over the bottom number, such as 120/80.

High blood pressure may be considered to be 140/90 mmHg or higher. However, it's difficult to give an example of a high blood pressure reading, because it depends on the individual. The level of blood pressure that is high for you depends on lots of different factors and your overall risk of heart attack or stroke. 

Generally, the lower your blood pressure, the better. If you have a history of heart disease, diabetes or a high risk of heart attack or stroke, it's recommended you lower your blood pressure to less than 130/80. See who needs to get their blood pressure checked.

High blood pressure doesn’t usually cause symptoms until it's very high, so it's usually found during an antenatal visit when you have your blood pressure checked.

High blood pressure in pregnancy can be diagnosed if your blood pressure is consistently high on 2 occasions. A sudden increase in blood pressure is often the first sign of a problem. Your midwife or LMC will also check if you have any of the symptoms listed above.

The type of treatment will depend on how high your blood pressure is and whether you have developed pre-eclampsia. You may need to be referred to an obstetrician (a doctor who specialises in maternity medicine) if you have severe high blood pressure and are at risk of developing pre-eclampsia.

If you only have high blood pressure and not pre-eclampsia, your blood pressure can usually be controlled by diet and lifestyle changes or antihypertensive medicines (medicines to lower your BP) and you can have a normal pregnancy. You will be taught the signs and symptoms of pre-eclampsia to watch out for as you must contact your midwife or healthcare provider if these symptoms develop.

If pre-eclampsia does develop, you will need much closer supervision and will probably need to have your baby early. The treatment and monitoring is aimed at keeping 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 treatment and monitoring for pre-eclampsia.

Some of the medicines that may be prescribed for you include:

• blood pressure lowering medicines such as labetalol, nifedipine or methyldopa
• low-dose aspirin from 12 weeks of pregnancy
• calcium
• magnesium sulphate to prevent seizures.

If you're started on medication for your blood pressure during pregnancy, keep taking this when you go into labour. You will have regular blood pressure checks during labour and after delivery.

Take the following steps to help control your blood pressure and have a healthy pregnancy:

• Attend all your antenatal check-ups so your healthcare provider or midwife can check your blood pressure and urine protein levels. 
• Know the signs and symptoms of pre-eclampsia and contact your midwife or LMC straight away if you have these.
• Don't smoke. This is one of the best things you can do to lower your blood pressure and help your baby be healthy. If you need help to quit smoking, talk to your healthcare provider.
• Gain an amount of weight that is healthy for you. Your doctor or midwife can help you set a pregnancy weight goal.
• Get regular gentle exercise during pregnancy. Walking or swimming several times a week can help lower blood pressure which is good for you and your baby. 
• Try to keep your stress level low. This may be hard to do, especially if you continue to work, have young children or have a hectic schedule. But try to find some time to relax.
  
  

Image credit: Healthify He Puna Waiora

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