Many women will require anaesthesia when they are pregnant, and some will be unaware that they are pregnant before attendance for surgery, especially in the first 2-3 months of their pregnancy. Studies have found incidences of up to 2.4% of unrecognised early pregnancy in preoperative testing.
Concerns with anaesthesia and surgery in early pregnancy are related to fetal loss and teratogenicity. A systematic review suggested that miscarriage rates may be slightly increased when surgery occurs in the first trimester; however, whether this is related to anaesthesia, surgery or the underlying pathological process necessitating surgery is difficult to say. A teratogen is a substance that causes structural or functional abnormality in a fetus exposed to that substance. The thalidomide catastrophe initiated the licensing arrangements for new drugs and their use in pregnancy; the current cautious stance of the pharmaceutical industry is reflected in the British National Formulary’s statement that no drug is safe beyond all doubt in early pregnancy.
Current evidence suggests that there is no increase in congenital abnormalities in women undergoing surgery and anaesthesia. However, concern has been raised over prenatal anaesthetic exposure and subtle functional neurocognitive changes. The anaesthetist should have a clear knowledge of the time scale of the developing fetus in order to balance the risks and benefits of any drug given to the mother.
Problems and special considerations
The possible effect of a drug can be considered against the stage of the developing fetus:
• Pre-embryonic phase (0-14 days post-conception). The fertilised egg is transported down the fallopian tube and implantation occurs at around 7 days post-conception.
The conceptus is a ball of undifferentiated dividing cells during this time and the effect of drugs on it appears to be an all-or-none phenomenon. Cell division may be slowed with no lasting effects or the conceptus will die, depending on the severity of the cell damage.
• Embryonic phase (3-8 weeks post-conception). Differentiation of cells into the organs and tissues occurs during this phase, and drugs administered to the mother may cause considerable harm. The type of abnormality that is produced depends on the exact stage of organ and tissue development when the drug is given.
• Fetal phase (9 weeks to birth). At this stage, most organs are fully formed, although the cerebral cortex, cerebellum and urogenital tract are still developing. Drugs administered during this time may affect the growth of the fetus or the functional development within specific organs, but structural changes are unlikely.
Management options
The anaesthetist should always consider the possibility of pregnancy in any woman of childbearing age who presents for surgery, whether elective or emergency, and should specifically enquire in such cases. If there is doubt, a pregnancy test should be offered; accepted practice is to delay elective surgery in pregnancy. If pregnancy is confirmed and surgery necessary, it would seem pragmatic to use systemic drugs after weighing up their necessity, benefits and risks while focusing on maintaining normal physiological parameters.
The use of nitrous oxide is now generally considered acceptable, despite its effects on methionine synthase and DNA metabolism, as there is little evidence that it is harmful clinically; however, it may be sensible to avoid as anaesthesia can be delivered safely without its use. Similarly, although the volatile agents have been implicated in impairing embryonic development, clinical evidence is lacking. Some drugs cross the placenta and exert their effect on the fetus - for example warfarin, which may cause bleeding in the fetus.
Key points
• The possibility of pregnancy should be considered in any woman of childbearing age.
• No drug is safe beyond all doubt in pregnancy.
Further reading
Allaert SE, Carlier SP, Weyne LP, et al. First trimester anesthesia exposure and fetal outcome: a review. Acta Anaesthesiol Belg 2007; 58: 119-23.
Cohen-Kerem R, Railton C, Oren D, Lishner M, Koren G. Pregnancy outcome following non-obstetric surgical intervention. Am J Surg 2005; 190: 467-73.
Perna RB, Loughan AR, Le JA, Hertza J. Prenatal and perinatal anesthesia and the long-term cognitive sequelae: a review. Appl Neuropsychol Child 2015; 4: 65-71.
Pregnancy I Procedures in early and mid-pregnancy