Prescribing during pregnancy

Pregnant women's needs are specific and require consideration when prescribing. By Dr Sara Whitburn.

In general practice one of our positive, but often quite daunting roles is the care of our pregnant and breastfeeding patients.

During this time women have specific needs that need to be considered when prescribing medication.

Women may contact their GP not only asking advice about health problems requiring treatment, but for advice about their pre-existing medication.

When prescribing during pregnancy and breastfeeding the health of both the mother and her child are important. The following general principles are helpful when thinking about prescribing new medication or the continuation of established medication during pregnancy and in breastfeeding:

  • Only prescribe when necessary; if non-pharmacological methods are available and would be adequate you should try these first.
  • Use treatments in the lowest effective dosage for the shortest period necessary.
  • Drugs with a better evidence base (generally more established drugs) are preferable.
  • Assess the benefit/risk ratio of the illness and treatment for both mother and baby and discuss this with your patient.

The main concern for both GPs and patients when prescribing is the possible effect on the fetus, or the teratogenicity of medications.

Teratogens are substances that can cause congenital malformations, spontaneous abortions or other structural or functional abnormalities in the fetus or the child after birth. Almost all drugs cross the placenta. Drugs might also affect the fetus indirectly by altering maternal homeostasis such as vascular flow.

Disease management
Women with chronic disease, such as diabetes, epilepsy, hypertension, asthma and thyroid disease often need to continue taking their drugs throughout pregnancy and sometimes change or increase their medication.

These women should be referred to secondary care for review. In other conditions such as maternal depression, the risk of acute illness can be a greater risk of harm than the risk of harm from medication and then the general principles above should be used to guide prescribing.

Some common conditions cause women to be symptomatically unwell, such as constipation, hay fever and nausea, and there are medications that are safe in pregnancy that can make women more comfortable.

A fear of potential teratogenicity of drugs is widespread among patients and the public. Pregnant and breastfeeding women may be less compliant that usual through fears of harming their unborn child.

In one study half of pregnant women said they would not take antibiotics prescribed by their doctor.

It is important to explain the benefits and risks of drug treatment in a balanced way.

Vitamins and supplements
Pregnant women should be advised to avoid self-medication with herbal remedies and should seek pharmacist advice when using OTC drugs.

Routine nutritional supplementation in pregnancy is a controversial subject because a normal diet should supply all the nutrients necessary for maternormal fetal development.

However, folic acid, and in some cases iron, has been found to be beneficial. Folic acid decreases the incidence of neural tube defects and cleft palates. It is recommended that women be encouraged to take 400 micrograms daily prior to and up to the twelfth week of pregnancy. Those with high risks of neural tube defect should take 5mg.

Iron-deficiency anaemia is often found during pregnancy. Routine iron supplementation is not recommended, but it has been suggested that iron supplementation should be considered when maternal concentration falls below 10g/dl. Iron supplementation should be continued for six weeks with mild anaemia.

As with the use of medicines in pregnancy, few studies have been done of the effects of drugs taken by a mother on her breast fed infant. Evidence of harm is based on case reports, clinical experience and anecdotal reports.

While the majority of medications pass into breast milk, most have no adverse effect on the infant's well-being when taken in therapeutic doses. The concentration of drugs likely to be prescribed to breastfeeding mothers is very low in breast milk.

When prescribing during breastfeeding, consider the age and health status of the infant. Prematurity, low birth weight or illness put an infant at higher risk of drug effects. Exposure to drugs in breast milk should be avoided in such infants.

Learning points
Prescribing in pregnancy and during breastfeeding:

1. Only prescribe when necessary.

2. Assess the benefit/risk ratio of the illness and treatment for both mother and baby/fetus.

3. Chronic conditions requiring medication throughout pregnancy should be reviewed by secondary care but there are safe alternatives for many common symptomatic conditions.

4. Compliance during pregnancy and breastfeeding can be low due to fears about teratogenicity of medication.

Dr Whitburn is a GP registrar in Dursley, Gloucestershire

Resources for prescribing during pregnancy

  • MIMS
  • BNF Appendix 4 and 5.
  • Neonatal Teratology Information Service, Regional Drug and Therapeutics Centre, Tel (01912) 321525 and information sheets at Toxbase (
  • UK Lactation Information and Advisory Service (
  • Briggs G, Freeman R, Yaffe S. Drugs in pregnancy and lactation. 6th Edition, Williams & Wilkins, Baltimore, 2001.

Have you registered with us yet?

Register now to enjoy more articles and free email bulletins


Already registered?

Sign in