(Date of issue: July 2016. Version: 1)
This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by Public Health England on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during pregnancy.
What are they?
Calcium channel blockers (CCBs) are a group of medicines mainly used to treat high blood pressure and to treat and prevent angina attacks. They include amlodipine, diltiazem, felodipine, lacidipine, lercanidipine, nicardipine, nifedipine, nimodipine, and verapamil. In the UK, the National Institute for Health and Care Excellence (NICE) recommends nifedipine as one of the medicines for treating high blood pressure during pregnancy. Nifedipine is also sometimes used to slow down or stop preterm labour.
Is it safe to use a calcium channel blocker other than nifedipine in pregnancy?
Nifedipine is the CCB for which the most information has been collected and is therefore commonly used in pregnancy. Although less information is available, there is no evidence that any of the other CCBs are harmful when used in pregnancy, and for some pregnant women with pre-existing high blood pressure, a doctor might recommend that staying on the CCB that was being used before pregnancy is the best course of action. It may also sometimes be necessary to use a specific CCB to treat a medical condition other than high blood pressure e.g. verapamil for an irregular heartbeat.
When deciding whether or not to take a CCB during pregnancy it is important to weigh up how necessary it 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.
This leaflet summarises the scientific studies relating to the effects of CCBs on a baby in the womb. Your doctor is the best person to help you decide what is right for you and your baby.
Can taking a calcium channel blocker in pregnancy cause my baby to be born with birth defects?
A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that some medicines are known to cause birth defects.
Studies of around 500 pregnant women who took a CCB in early pregnancy have not shown that they were more likely to have a baby with a birth defect compared to women not taking CCBs. Three studies have all shown no link between taking a CCB in pregnancy and having a baby with a heart defect.
However, because birth defect rates have been studied in a relatively small number of babies born to pregnant women using CCBs, and there is currently no information on specific CCBs, further research is required to address this question.
Can taking a calcium channel blocker in pregnancy cause miscarriage?
One study of around 300 pregnant women taking a CCB showed that miscarriage among these women was no more common than in women not taking a CCB. The results of this study are likely to be reliable as the most appropriate technique to analyse miscarriage rates was used. A further smaller study did show an increased risk of miscarriage in women using CCBs, but the information in this study was not analysed using the most accurate method. There are no published studies on miscarriage rates in women using specific CCBs. Although the results of the larger study are reassuring, CCBs were assessed as a group and further studies of specific CCBs using accurate analysis methods are required.
Can taking a calcium channel blocker in pregnancy cause stillbirth?
Overall, the data from a number of small studies does not indicate that use of nifedipine in pregnancy increases the risk of stillbirth. However, further research into this subject is required as stillbirth rates have been studied in a relatively small number of pregnant women using nifedipine and there is currently no information on other CCBs.
Can taking a calcium channel blocker in pregnancy cause preterm birth or low birth weight in the baby?
It is not currently possible to say whether use of CCBs in pregnancy increases the risk of preterm birth or low birth weight in the baby, as the available published studies mainly consist of trials where the medicines were given to pregnant women who often had serious medical conditions and only for a short period just before the birth of the baby. Further studies of pregnant women who took CCBs for longer periods are therefore required to answer these questions.
Can taking a calcium channel blocker in pregnancy cause learning or behavioural problems in the child?
A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.
Three small studies that have investigated whether children aged between 18 months and 12 years who were exposed in the womb to nifedipine were at increased risk of learning and behavioural problems compared to children not exposed to nifedipine. All produced reassuring results. However, larger studies that assess other aspects of learning and behaviour, including in children exposed in the womb to individual CCBs, are required.
Will my baby need extra monitoring during pregnancy?
As part of their routine antenatal care most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects and to check the baby’s growth.
There is no evidence that taking a CCB during pregnancy causes any problems that would require extra monitoring of your baby. However, pregnant women with high blood pressure and some of the other conditions that CCBs are used to treat might receive extra monitoring during pregnancy to ensure that they remain healthy and that the baby is growing and developing as expected.
What if I have already taken a calcium channel blocker during pregnancy?
Although CCBs do not appear to be harmful to a developing baby it is always a good idea to let your doctor know that you are pregnant or if you have taken any medicines. You can decide together whether you still need the medicines that you are on and to make sure that you are taking the lowest dose that works.
Are there any risks to my baby if the father has taken a calcium channel blocker?
We would not expect any increased risk to your baby if the father took a CCB before or around the time you became pregnant.
Who can I talk to if I have questions?
If you have any questions regarding the information in this leaflet please discuss them with your health care provider. They can access more detailed medical and scientific information from www.uktis.org.
Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks. They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.
Medicines use in pregnancy
Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby. There are, however, some medicines that can harm a baby’s normal development. How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.
If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.
When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.
Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider. It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.