Preterm labor and Surg

As many as 2% of pregnant women undergo anesthesia for non-obstetric surgery during their pregnancy [Rosen, 1999]. The second trimester is considered the safest time to undergo nonobstetric surgery (once organogensis is completed), but there are still concerns of fetal hypoxia due to increasing metabolic demands and accidental induction of premature labor. In a study to evaluate the safety and timing of abdominal surgery during pregnancy, 77 gravid patients undergoing nonobstetric abdominal surgery were retrospectively reviewed for clinical presentation, perioperative management, preterm labor, and maternal and fetal morbidity and mortality. Preterm labor occurred in 26% of the second-trimester patients and 82% of the third-trimester patients. [Visser, et al., 2001].

The Duncan study of 2565 pregnant Canadian women was notable in that it showed a statistically significant increase in the risk of spontaneous abortion in both the first and second trimesters (from 6.5 to 7.1%) in those pregnant women undergoing surgery [Duncan et al., 1986]. In another study, 22% of 778 patients who underwent appendectomy between 24 to 36 weeks gestation delivered within first week after surgery. However, there was no increased risk of preterm delivery after that initial week after surgery. [Mazze and Kallen, 1991].

It is generally thought that it is the pathology leading to surgery is more likely to induce preterm labor than the surgery itself. Outcomes studies in large numbers of women who underwent surgery during pregnancy show no increase in congenital abnormalities, but a greater risk of abortion, growth restriction, and low birth weight. This suggests that it is the surgical disease or procedure rather than the exposure to anesthesia that can increase the risk of preterm labor [Goodman, 2002].

If the fetus is viable, there is a preference towards regional anesthesia instead of general anesthesia, if possible. Intraoperative preterm labor can potentially be treated with the same agents used to treat preterm labor outside of the operative room. These agents include: terbutaline (ß2-agonist), magnesium, indomethacin, or calcium channel blockers. It is unclear if prophylactic tocolytics affect outcome and they can be associated with side effects, so routine use is not indicated at this time. If surgery must occur during a pregnancy, and if the patient and her obstetrician are willing to perform a C-section intraoperatively (usually only after 24 weeks gestational age), one should monitor uterine activity and fetal heart rate intraoperatively, and a neonatologist should be available. [Barron, 1985].