Oral contraceptives

What are oral contraceptives?

There are two types of oral contraceptive. 

The first, often called ‘the combined pill’ or ‘the pill’, contains synthetic versions of two hormones, oestrogen and progesterone.

The second type of oral contraceptive, known as the ‘progestogen-only pill’ or ‘the mini pill’ contains synthetic progesterone only.

Different brands of oral contraceptive may contain hormones in different forms and strengths.

There is quite a lot of information about babies whose mothers took oral contraceptives whilst pregnant. However, most studies have looked at oral contraceptives as a group rather than trying to examine the effects of each type of pill separately. The findings of these studies are summarised below.

Can taking oral contraceptives 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 large numbers of pregnant women do not prove that there is a link between oral contraceptive use in early pregnancy and birth defects in the baby.

Oral contraceptives contain sex hormones, and so some studies have specifically looked at whether taking oral contraceptives during early pregnancy may affect the development of a baby’s sex organs. There is no scientific proof from these studies that women taking oral contraceptives during pregnancy are more likely to have a baby with abnormal sex organs, or to have a baby boy with hypospadias (where the opening of the penis is not in the usual place).

While some studies have suggested a possible link between oral contraceptive use in pregnancy and having a baby with limb reduction defects (shortened or missing arms or legs), the majority of studies have not shown this. Experts agree that the available information does not prove a link but that ongoing research is ideally required.

Can taking oral contraceptives in pregnancy cause miscarriage?

No increased chance of miscarriage was identified in three studies of women who took oral contraceptives during pregnancy. While this is reassuring, because only around 1,800 women were studied, further research into the likelihood of miscarriage is ideally required.

Can taking oral contraceptives in pregnancy cause preterm birth or my baby to be small at birth (low birth weight)?

Two studies have investigated whether preterm birth may be linked to exposure to oral contraceptives in early pregnancy. The studies each produced different results. More research is therefore needed to determine whether the link identified in one study was due to oral contraceptive use itself, or to other factors that may have been more common in women who had taken oral contraceptives in early pregnancy (see below).

There is also mixed evidence as to whether taking oral contraceptives in early pregnancy may be linked to low birth weight in the baby (<2,500 g). While two studies have shown a possible link, one further study did not.  

Pregnancies in women taking the contraceptive pill are generally unplanned and may not be detected until later. Women who do not realise they are pregnant are unlikely to be following pregnancy lifestyle advice. This may explain why some studies have found that babies of women taking oral contraceptives in pregnancy are more likely to be born earlier and be smaller.

Can taking oral contraceptives in pregnancy cause stillbirth?

No studies have specifically investigated whether stillbirth is more common following use of oral contraceptives in pregnancy.

Can taking oral contraceptives 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.

No studies have assessed the learning and behaviour of children exposed in the womb to oral contraceptives.

Will my baby need extra monitoring?

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.

Extra monitoring of your baby is not required if you have taken oral contraceptives during pregnancy.

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 healthcare provider. They can access more detailed medical and scientific information from www.uktis.org.