Surgery and anesthesia may pose risks to an unborn fetus. Some of this risk is medico-legal, however this risk is very low. According to the American Society of Anesthesiology, only seven out of 10,500 claims in the Anesthesia Closed Claim database were regarding undiagnosed pregnancy prior to surgery. Much of this risk, however, is theoretical; none of the anesthetic agents currently in use have been shown to have teratogenic effects when used under standard protocols. Because the utility of preoperative pregnancy tests (POPT) hasn't been clearly elucidated in the literature, the guidelines for their use are currently per patient preference.
To fill this knowledge gap and potentially inform guidelines on preoperative pregnancy tests, researchers performed a systematic review on the existing literature on the utility and cost-effectiveness of POPT, as well as the incidence of unrecognized pregnancy in India. They found that "patient-reported pregnancy status is highly accurate, with a 99.7% negative predictive value." Additionally, incidence of previously unknown pregnancy on the day of surgery is extremely low, with one true-positive outcome out of 647 patients tested. These findings support the notion that preoperative pregnancy tests may not be necessary, as the tests are similarly accurate to patient report, and the outcomes they screen for are rare.
However, the risk of poor neonatal and maternal outcomes must be considered. Uterine surgery may interrupt blood flow to the uterus and placenta, and thus are high-risk for pregnant patients. However the data for non-obstetric and non-uterine surgeries is less clear. One Canadian study found an increased risk of spontaneous abortion after exposure to general anesthesia, while one Swedish registry study found an association between anesthesia exposure and low birth weight. Data investigating first-trimester anesthetic exposure effect on fetal outcomes are confounded by multiple factors including the independently high rate of miscarriage during first trimester and the difficult-to-quantify effects of the physiologic stress of surgery itself. Furthermore, most studies on this topic have a small-sample size and are not typically generalizable.
To combat this, Balinskaite et al. performed a retrospective cohort study with data from almost 6.5 million pregnancies within the English National Health System hospitals between 2002 and 2012, of which a little over 47,000 patients underwent non-obstetric surgery during their pregnancy. They found that, overall, the risk of adverse neonatal outcomes was similar in patients undergoing surgery when compared to patients who weren't. However, this study could not quantify the effect of maternal health conditions on the risk of poor outcomes, and thus a patient-specific approach is still recommended when planning for surgery in pregnant patients.
In sum, the data shows that preoperative pregnancy tests may not have a lot of utility when used preoperatively for patients undergoing non-obstetric surgeries. However due to the low cost of pregnancy tests and a lack of evidence about which specific patient factors modulate the risk of surgery and anesthesia on birth outcomes, the ASA recommends that "POPT should be offered to all patients of childbearing age undergoing surgery, and that the decision to receive testing should be per patient preference."