The effects of certain medications during pregnancy may be tested in exams, and they are worth being aware of when prescribing for women that are, or could be, pregnant. This is not an exhaustive list, and when in doubt always check the BNF, guidelines and with seniors when prescribing in pregnancy.
Non-Steroidal Anti-Inflammatory Drugs
Examples of non-steroidal anti-inflammatory drugs (NSAIDs) are ibuprofen and naproxen. They work by blocking prostaglandins. Prostaglandins are important in maintaining the ductus arteriosus in the fetus and neonate. Prostaglandins also soften the cervix and stimulate uterine contractions at the time of delivery.
NSAIDS are generally avoided in pregnancy unless really necessary (e.g. in rheumatoid arthritis). They are particularly avoided in the third trimester, as they can cause premature closure of the ductus arteriosus in the fetus. They can also delay labour.
Beta-blockers are commonly used for hypertension, cardiac conditions and migraine. Labetalol is the most frequently used beta-blocker in pregnancy, and is first-line for high blood pressure caused by pre-eclampsia.
Beta-blockers can cause:
- Fetal growth restriction
- Hypoglycaemia in the neonate
- Bradycardia in the neonate
ACE Inhibitors and Angiotensin II Receptor Blockers
Medications that block the renin-angiotensin system (ACE inhibitors and ARBs) can cross the placenta and enter the fetus. In the fetus, they mainly affect the kidneys, and reduce the production of urine (and therefore amniotic fluid). The other notably effect is hypocalvaria, which is an incomplete formation of the skull bones.
ACE inhibitors and ARBs, when used in pregnancy, can cause:
- Oligohydramnios (reduced amniotic fluid)
- Miscarriage or fetal death
- Hypocalvaria (incomplete formation of the skull bones)
- Renal failure in the neonate
- Hypotension in the neonate
The use of opiates during pregnancy can cause withdrawal symptoms in the neonate after birth. This is called neonatal abstinence syndrome (NAS). NAS presents between 3 – 72 hours after birth with irritability, tachypnoea (fast breathing), high temperatures and poor feeding.
Warfarin may be used in younger patients with recurrent venous thrombosis, atrial fibrillation or metallic mechanical heart valves. It crosses the placenta and is considered teratogenic in pregnancy, therefore it is avoided in pregnant women. Warfarin can cause:
- Fetal loss
- Congenital malformations, particularly craniofacial problems
- Bleeding during pregnancy, postpartum haemorrhage, fetal haemorrhage and intracranial bleeding
The use of sodium valproate in pregnancy causes neural tube defects and developmental delay.
There are strict rules for avoiding sodium valproate in girls or women unless there are no suitable alternatives and strict criteria are met to ensure they do not get pregnant. There is a specific program called Prevent (valproate pregnancy prevention programme) to ensure this happens.
Lithium is used as a mood stabilising medication for patients with bipolar disorder, mania and recurrent depression. It is avoided in pregnant women or those planning pregnancy unless other options (i.e. antipsychotics) have failed.
Lithium is particularly avoided in the first trimester, as this is linked with congenital cardiac abnormalities. In particular, it is associated with Ebstein’s anomaly, where the tricuspid valve is set lower on the right side of the heart (towards the apex), causing a bigger right atrium and a smaller right ventricle.
When lithium is used, levels need to be monitored closely (NICE says every four weeks, then weekly from 36 weeks). Lithium also enters breast milk and is toxic to the infant, so should be avoided in breastfeeding.
Selective Serotonin Reuptake Inhibitors
Selective serotonin reuptake inhibitors (SSRIs) are the most commonly used antidepressants in pregnancy. SSRIs can cross the placenta into the fetus. The risks need to be balanced against the benefits of treatment. The risks associated with untreated depression can be very significant. Women need to be aware of the potential risks of SSRIs in pregnancy:
- First-trimester use has a link with congenital heart defects
- First-trimester use of paroxetine has a stronger link with congenital malformations
- Third-trimester use has a link with persistent pulmonary hypertension in the neonate
- Neonates can experience withdrawal symptoms, usually only mild and not requiring medical management
Isotretinoin is a retinoid medication (relating to vitamin A) that is used to treat severe acne. It should be prescribed and monitored by a specialist dermatologist.
Isotretinoin is highly teratogenic, causing miscarriage and congenital defects. Women need very reliable contraception before, during and for one month after taking isotretinoin.
Last updated September 2020