Summary
Morphine is an opioid analgesic most commonly administered orally, intravenously or rectally for the treatment of severe or intractable pain.
Data relating specifically to morphine exposure in human pregnancy are extremely limited. It is not currently possible to exclude a teratogenic effect.
There are no controlled studies of the effect of morphine exposure on the incidence of miscarriage and no robust evidence of an increased malformation risk. Increased rates of specific malformations have been observed in some studies analysing opioids as a class, but the data are conflicting and the studies confounded. Data are extremely limited in relation to low birth weight, preterm delivery, stillbirth and neurodevelopmental outcomes, but a possible association with altered fetal growth in utero and visual defects (strabismus) have been reported, the clinical significance of which is unclear. Codeine, another opioid analgesic, is metabolised to morphine. Data are similarly limited and are reviewed in a separate UKTIS monograph.
Owing to the lack of data regarding malformation risks, women who have been exposed to morphine in the first trimester are particularly encouraged to attend their routine detailed fetal anomaly scan, which is generally conducted at around 18 to 20 weeks of pregnancy. Use of any opioid during pregnancy, particularly around the time of delivery, confers a risk of neonatal respiratory depression and neonatal withdrawal. Delivery in a hospital setting is therefore advisable.
Where morphine poisoning or overdose occurs in pregnancy, maternal toxicity is likely to be a major factor in determining risk to the fetus. If use of an antidote (e.g. naloxone) is required in the management of maternal toxicity, it should not be withheld on account of pregnancy.
Exposure to morphine at any stage in pregnancy would not usually be regarded as medical grounds for termination of pregnancy. However, other risk factors may be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments.
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