Pregnancy is usually considered in 3 x three- month periods (trimesters).
The first trimester=important for formation and development of foetus and placenta. Differentiation of foetal organs can occur during this time, and can be disturbed by external stimuli. Therefore, only essential drugs with a proven safety record should be permitted.
Middle trimester= No absolute contraindication to GA but not really wanted (can be done as long as there is good oxygenation for the patient at all times), as essential foetal development is complete and fundus isn't large enough to affect venous return.
Final trimester= volume of uterus causes most problems. May obstruct venous return from legs by putting pressure on lower vena cava. Reduced venous return= reduced cardiac output. Anaesthetics in supine position should be avoided and managing syncope should be with head in lateral and not supine position. Upwards pressure from fundus may cause delayed vomiting, which if inhaled could be life threatening.
Maternal blood may be increased by 20% therefore increased dose of anaesthetics may be necessary. Pregnancy changes the mothers metabolism, therefore the patient will usually have to stay in hospital.
Ref:
Girdler NM, Hill CM, Wilson KE. Clinical sedation in dentistry. John Wiley & Sons; 2009 May 11.
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