Drugs and pregnancy

Up to 90 per cent of women take prescription or non-prescription medicines or illegal substances, knowingly or unknowingly, during pregnancy. These are commonly taken in the first few weeks before a woman is aware of her pregnancy.

Because all substances taken into a pregnant woman's body move from the mother to the foetus, primarily through the placenta, the developing foetus is exposed to all chemicals the mother is.

The effect a drug has on the foetus depends on the drug itself and the stage of development the foetus is at when the drug is taken. Between days 17 to 57 after fertilisation, the foetus is particularly susceptible to harm. This is the period during which vital organs and the nervous system are developing. Drugs reaching the foetus at this stage could cause miscarriage, deformity or a subtle defect that may be detected only later in life.

Drugs taken after organ development is complete may not cause obvious birth defects, but may alter the growth and function of organs and tissues.

The extent to which drugs taken by the mother affect her unborn child, was shockingly illustrated by the sedative drug, thalidomide, which was prescribed for scores of pregnant women in the 1950s and 1960s. The drug resulted in birth defects such as severely underdeveloped arms and legs and defects of the intestine, heart, and blood vessels.

Doctors now prefer to err on the side of caution, advising pregnant women to avoid taking any medicine, if possible. However, the need to protect the foetus from damage has to be weighed up against the need to care for the mother in cases where a woman suffers from a serious health condition. It is often possible to replace a woman's chronic medication with an alternative that is less likely to damage the foetus during pregnancy.

Drugs known to harm the foetus

Certain drugs are known to harm the foetus. These include:

  • Cancer treatments such as dermatogens, which can cause such birth defects as stunted growth in the uterus (intrauterine growth retardation), underdevelopment of the lower jaw, cleft palate, abnormal development of the skull bones, spinal defects, ear defects, clubfoot, and mental retardation
  • Certain antibiotics may cross the placenta to be stored in the bones and teeth, resulting in slow bone growth and soft tooth enamel. Other antibiotics may result in deafness, joint abnormalities, jaundice and brain damage
  • Isotretinoin (Roaccutane), which is used to treat severe acne, psoriasis, and other skin disorders, causes major birth defects. These can include heart defects, small ears, and hydrocephalus (water on the brain)
  • Androgenic (masculinising) hormones, used to treat various blood disorders, and synthetic progestins taken during the first 12 weeks of pregnancy may masculinise a female foetus's genitals
  • Diethylstilbestrol (DES), a synthetic oestrogen, can cause vaginal cancer, menstrual problems and reproductive system problems in girls whose mothers took this drug during pregnancy. Boys exposed to the drug during pregnancy may have penis abnormalities
  • Cyclizine frequently taken for motion sickness, nausea, and vomiting may cause birth defects
  • Anticonvulsant drugs taken during pregnancy may cause the baby to have a cleft palate and abnormally developed heart, face and skull, hands, or abdominal organs. The baby may also be mentally retarded
  • Radioactive iodine given to a pregnant woman to treat an overactive thyroid gland (hyperthyroidism) can cross the placenta and destroy the foetus's thyroid gland or cause severe under-activity of the thyroid gland (hypothyroidism)
  • Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen (Brufen), can reach the foetus in significant amounts if taken by a pregnant woman. Taking large doses of aspirin or other NSAIDs during pregnancy may delay the start of labour, and may dangerously reduce the amount of amniotic fluid surrounding the foetus
  • Anti-anxiety drugs and antidepressants may cause birth defects when taken during the first three months of pregnancy
  • Oral hypoglycaemic drugs are given to lower blood sugar (glucose) levels in people who have diabetes, but they often fail to control diabetes in pregnant women and may cause newborns to have very low blood glucose levels (hypoglycaemia). Therefore, insulin is preferred for treating diabetes in pregnant women
  • Anticoagulant drugs such as warfarin, can cause significant birth defects if taken during the first three months of pregnancy
  • Drugs for treating heart and blood vessel disorders can also cause problems in the foetus. However, the risk to the mother of pre-eclampsia or eclampsia is usually thought to outweigh the risks to the foetus in these cases
Smoking during pregnancy is likely to result in low birth weight babies and increases the risk of miscarriage, stillbirth, premature birth, and sudden infant death syndrome (SIDS).

Drinking alcohol during pregnancy can cause foetal alcohol syndrome and birth defects such as small heads (microcephaly), facial abnormalities, and borderline mental deficiency. Babies may also have joint abnormalities and heart defects, and are more likely to die soon after birth.

Use of illegal drugs such as cocaine during pregnancy increases the risk of miscarriage; early detachment of the placenta from the uterus; brain defects and defects of the kidneys and genitals. Babies may also be born addicted to the illegal substance, and will have to endure painful withdrawal symptoms after birth.

The effects of many other drugs taken during pregnancy are not known, mainly because it is too dangerous for drug testing to be carried out on pregnant women. Ideally, you should avoid all over-the-counter and prescription drugs throughout your pregnancy, and try treating mild ailments with other, safer self-help measures. These could include mild herbal teas, massage and aromatherapy baths (use only essential oils recommended for use during pregnancy).

If you have any serious drug concerns or nagging symptoms, consult your health care practitioner about safe drug use before you take anything.