(Date: October 2016. Version: 2)

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.

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Primodos and Hormonal Pregnancy Tests review underway

An Expert Working Group of the Commission on Human Medicines has been set up to consider all available evidence, including previously unpublished and unassessed information, on Primodos and Hormonal Pregnancy Tests.  This information leaflet, the content of which is based on an assessment of the published evidence in 2012, will be updated to reflect the findings of the review once it is concluded.

What is it?

Primodos was a hormonal pregnancy test taken by mouth in tablet form which caused a vaginal bleed (period) in women who were not pregnant. It was available in the UK from 1953 to 1975. The active ingredients in Primodos were the synthetic hormones norethisterone acetate and ethinyloestradiol. After the development of urine pregnancy tests in the early 1970s Primodos was withdrawn from sale.

Did Primodos cause babies to be born with birth defects?

 In the mid-1960s the possibility that Primodos caused birth defects in babies of women who took it in early pregnancy was raised.

In the 1970s and 1980s a number of large scientific studies were carried out using medical information collected about children born to pregnant women who had used Primodos and other similar hormonal pregnancy tests. Nearly all of these studies showed that use of hormonal pregnancy tests did not increase the risk of birth defects in the baby. More recent studies of pregnant women who took oral contraceptives (“the pill”) in pregnancy, which contain similar types of hormones to Primodos, have also not provided convincing evidence of a link with birth defects in the baby.

Many of the studies of Primodos use in pregnancy were carried out some time ago when techniques for data collection and analysis were not as advanced as they are today. Additionally, the studies often relied on mothers remembering at what stage of pregnancy they took Primodos and how many tablets they had taken a long time after their pregnancies. Because these factors can result in inaccuracies in the information that was analysed, it is not possible to completely rule out that Primodos caused birth defects in some babies. However, overall the available information is reassuring and there is no evidence from these studies that Primodos caused birth defects.

What if I have birth defects and my mother took Primodos?

Anyone who is questioning whether their birth defects may have been caused by exposure to a specific medicine in the womb should be referred to a specialist doctor called a ‘Clinical Geneticist’. Very advanced genetic tests are now available through the NHS to look for ‘spelling errors’ (mutations) in a person’s genes that cause birth defects. It is important to consider whether your birth defects are due to a genetic fault because mutations can be hereditary and could therefore be passed on to your children or grandchildren. A geneticist will be able to discuss the chance of this happening and the options available to you and your family for future pregnancies.

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

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General information 

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.

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.

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