Cardiopulmonary bypass during pregnancy is associated with similar maternal mortality to that outside pregnancy [
2,
3]. However, the foetal mortality rate is 14 to 33% [
1,
3,
14]. Sustained uterine contractions resulting in uteroplacental hypoperfusion and foetal hypoxia are considered the most important cause of foetal death [
14]. Causative factors for uterine contractions are haemodilution, causing dilution of progesterone, as well as cooling and rewarming. Nonpulsatile flow triggers vasoconstriction, further increasing placental dysfunction [
14]. Uteroplacental flow is further compromised by decrease in maternal blood pressure. Foetal bradycardia is often observed. Although the mechanism of this bradycardia is not known, foetal hypoxia due to haemodilution and to uteroplacental hypoperfusion probably plays a role [
14]. In addition to foetal mortality, significant morbidity including late neurological impairment has been described, mainly associated with premature birth [
2,
3]. Because of these risks, cardiac surgery should be avoided whenever possible. In the first trimester the risk of foetal malformations is higher, therefore postponement of cardiac surgery until after the 13th week of gestation is preferred. It is recommended to monitor uterine contractions and foetal heart rate during surgery. To diminish the risk of foetal bradycardia and uterine contractions, the European Society of Cardiology guidelines recommend to minimise cardiopulmonary bypass time and to maintain a pump flow > 2.5 l/min/m
2, a perfusion pressure > 70 mm Hg, a maternal haematocrit > 28%, and to use pulsatile flow and normothermic perfusion [
2]. Additionally a left lateral tilt of 15º is recommendable to relieve pressure of the uterus on the caval vein.
Because of the high foetal risk, when gestational age is advanced, it should be considered to deliver the baby before cardiac surgery. However, it is a matter of debate at which gestational age pre-surgery delivery is advantageous for the foetus, since premature birth is in itself associated with foetal mortality and morbidity. Although the prognosis of very premature babies has improved in recent years, before 26 weeks of gestation neonatal mortality is around 40% and delivery before surgery is not recommended. After 28 weeks of gestation, neonatal mortality is < 10% and severe morbidity is limited; therefore, the guidelines recommend that delivery before cardiopulmonary bypass should be considered. If possible the surgery should be delayed until a full course of corticosteroids (at least 24 h) has been administered to the mother, since this improves foetal outcome considerably [
2]. Between 26 and 28 weeks the prognosis of the baby depends on gender, estimated birth weight, the presence of foetal malformations, and the administration of corticosteroids. Additionally the experience of the local neonatal unit is important in the decision whether or not to perform a caesarean section before cardiopulmonary bypass. The decision should be made on an individual basis [
2]. It should be kept in mind that maternal prognosis may be negatively influenced by surgery shortly after delivery, therefore delivery should only be performed when the advantages for the baby are clear [
15].