Teratology: medicines, alcohol and birth defects

Teratology is a medical field concerned with how exposures in pregnancy affect development. A teratogen is anything that can cause a structural or functional change in a developing baby. Medicines are one group. Others include alcohol, some infections and certain chemicals.

Teratology is not a condition that a person has. This page sits alongside condition guides because families often search for it after taking a medicine before they knew they were pregnant, or while planning a pregnancy with a long-term condition. The practical question is nearly always the same: what is known about this exposure, at this dose, at this stage of pregnancy?

UKTIS describes itself as providing evidence-based safety information about medication, vaccine, chemical and radiological exposures in pregnancy.

Newcastle Hospitals explains that organ formation happens in the first three months. Exposure in that window is more likely to cause structural problems such as a malformed heart or limb. Later exposure tends to affect growth. Because many pregnancies are not recognised for several weeks, planning ahead is helpful where possible.

The UKTIS summary on methotrexate shows how dose changes the picture. It says fetal risks are largely dose dependent. High-dose methotrexate used for ectopic pregnancy is a teratogen, with case reports describing a pattern of skull and face, digit, spine and rib defects after exposure most commonly between 4 and 8 weeks. For the low doses used in autoimmune disease it says data are too limited to quantify the absolute risk, and advises extra fetal monitoring.

The mother's illness is part of the balance. Newcastle Hospitals says the risk to the fetus must always be balanced with the risk to the woman if a medication is stopped. An untreated illness can itself harm a pregnancy.

Newcastle Hospitals lists several medicines for health professionals to be aware of. They include certain blood pressure medicines (ACE inhibitors, which can cause problems in the second and third trimesters), statins, most anti-epilepsy drugs, vitamin A preparations, warfarin and lithium. Herbal medicines are described as having little safety information in pregnancy.

These are examples, not instructions. A medicine named in guidance may still be the right choice for a particular person after specialist review, and an unlisted one may not be. The NHS says that some types of epilepsy medicine can harm a baby if taken in pregnancy, and that if you or your partner take epilepsy medicine and could conceive, you should discuss treatment with a specialist.

Do not stop or switch any medicine because of a list. Speak to the prescriber, and ask whether UKTIS or Bumps information is available for the medicine.

Alcohol is a well-established teratogen. The NHS says alcohol in the mother's blood passes to the baby through the placenta, the baby cannot process it well, and it can damage the brain and body and stop normal development in the womb. This can result in loss of the pregnancy, and surviving babies may have lifelong problems called fetal alcohol spectrum disorder (FASD).

The NHS lists possible effects on movement, balance, vision and hearing, learning, emotions and social skills, impulse control, speech, and the joints, muscles, bones and organs such as the kidneys and heart. These problems are permanent, though early support can limit their impact. The more a mother drinks, the more severe the symptoms tend to be.

FASD is completely avoidable if you do not drink alcohol while pregnant, according to the NHS, which says there is no proven safe level. If you are struggling with alcohol, speak to a midwife or doctor. The NHS page points to confidential help and support services.

The NHS refers people to Bumps (Best Use of Medicines in Pregnancy), which Bumps describes as freely available, reliable, evidence-based information to help women make decisions that are best for both mother and baby. Its leaflets are based on the scientific material UKTIS produces for health professionals.

The NHS says that if you cannot find a medicine on Bumps, your doctor, midwife or pharmacist can contact UKTIS on your behalf. UKTIS also runs the MyBump portal for pregnant women who want to contribute to research on medicine safety.

The NHS adds that not all natural remedies are safe in pregnancy. Some products may be poor quality or contain harmful substances such as lead. It advises telling your midwife, doctor or pharmacist if you use herbal, homeopathic or aromatherapy products.

The first contact is usually the GP, community midwife or pharmacist. Specialist input comes from obstetric medicine, clinical genetics, fetal medicine and, for medicine safety questions from clinicians, UKTIS.

Private obstetric and fetal medicine services are also available for reassurance scans. Ask whether they will liaise with your NHS maternity team and prescriber so that advice is consistent.

The NHS advises that if you take regular medicine and are planning a baby, talk to your doctor ideally before you start trying, or as soon as you find out you are pregnant. Newcastle Hospitals says the aim is that potentially teratogenic medicines can be stopped, switched or reduced to the lowest possible dose, always balanced against the woman's own health.

If you have already taken a medicine, do not panic. The UKTIS methotrexate summary shows the typical approach after a possible teratogen: a specific risk assessment, focused anomaly scans and close monitoring of fetal growth. Women are made aware of the limitations of those tests.

UKTIS notes that other risk factors may be present in individual cases which can independently increase the risk of an adverse outcome, so assessment is individual.

For many medicines, evidence on pregnancy is limited. UKTIS statements often say data are too limited to quantify risk, or that studies are small. That is not the same as showing harm, and it is not the same as showing safety. Newer medicines in particular may have little human data.

Contact your GP, midwife or pharmacist if you take regular medicine and are pregnant or planning to be, and do so before changing anything. The NHS says to make sure any doctor, dentist or other professional who prescribes or treats you knows you are pregnant.

Call 111 or your maternity unit for urgent concerns in pregnancy such as bleeding, severe pain or reduced baby movements. Call 999 for emergencies. If you drink alcohol heavily, do not stop suddenly without medical advice, because withdrawal can be dangerous. Ask for help from a midwife or doctor.