Is Routine Preoperative Pregnancy Testing Necessary?

INTRODUCTION

Surgery on a pregnant woman raises several novel concerns. These include the effect of surgery and anesthesia on the developing fetus and the potential to trigger preterm labor. The hazards to the fetus could come from teratogenic effects of drugs administered during the perioperative period or, in a more advanced pregnancy, alterations in uteroplacental blood flow and maternal hypoxia and acidosis. It is reported that up to 15% of known pregnancies miscarry before 20 weeks, and up to 50% of unrecognized pregnancies miscarry during the first trimester. Because the period of organogenesis is during the first trimester, elective surgery is usually postponed to avoid potential teratogenicity and intrauterine fetal death. Although it is unclear which factors account for it, increased risk for spontaneous abortion is observed in women undergoing general anesthesia during the first or second trimester of pregnancy. Premature labor is more likely in the third trimester. Some studies, including one large retrospective cohort review, ⁶ have also suggested the presence of a strong association between central nervous system (CNS) defects, such as microcephaly, and first-trimester anesthesia exposure.

Consequently, the issue of ruling out pregnancy before surgery is a crucial one. Unfortunately, medical history alone is often unreliable in ruling out pregnancy, especially in the adolescent female population. On one hand, it is in this adolescent female population that obtaining a routine pregnancy test may present an ethical and legal problem. These patients may refuse to have the test done and may in some states have the legal right to keep that information private from their parents. On the other hand, adult women may very well have the same or a higher risk for unknown pregnancy before a surgical procedure compared with adolescents. ^, Routinely testing patients for pregnancy may present a trust issue with women who believe that their history excludes that possibility. Furthermore, calculation of the cost incurred if pregnancy screening is done routinely before each surgery adds to the controversy of the issue.

OPTIONS

Should preoperative pregnancy testing be performed on all female patients of childbearing age or just in select populations? Whether these select populations should include only those whose history is suggestive of pregnancy or whose history is unclear is still unresolved. The general practice of anesthesiologists differs across institutions, as well as by personal judgments and convictions. Instituting policies for preoperative pregnancy testing should be based on the patient's best interests in correspondence with state law and ethical responsibility.

The American Society of Anesthesiologists (ASA) Committee on Ethics has stated that patients should be offered but not required to undergo pregnancy testing unless there is a compelling medical reason to know that the patient is pregnant.

The ASA Practice Advisory for Preanesthesia Evaluation was subsequently amended by the ASA House of Delegates in 2003, and the language from the ASA task force has largely remained stable as indicated by the ASA House of Delegates statement in 2016: “Pregnancy testing may be offered to female patients of childbearing age and for whom the result would alter the patient's management.” Additionally, the statement reinforces the importance of a quality informed consent, recommending that preanesthetic education materials should include information about false positives and negatives of pregnancy testing and the inadequacy of scientific literature to inform patients or physicians of the unknown harmful effects of anesthesia during early pregnancy.

Two of the most common policies on preoperative pregnancy testing were outlined in an ASA newsletter from 2006 and are still relevant to common current practice. One approach is to test every female patient of childbearing potential regardless of whether she consents. The justification for this is that consent to surgery and anesthesia is also consent to a pregnancy test. An alternative policy is one that allows patients to refuse testing after anesthetic and surgical risks to a possible pregnancy have been explained. After refusal, however, the patient is asked to waive all legal rights relating to undetected pregnancy. In some institutions, the patient is informed and consulted but may be tested regardless of whether there is consent. Kerai and colleagues recently conducted a literature review and arrived at a similar model for pregnancy testing but incorporated slightly less aggressive language, stating, “as there is no means to disentangle composite effects of anesthesia exposure, surgery and underlying conditions for which surgery is undertaken, it is imperative to offer POPT [preoperative pregnancy testing] to all women surgical patients.”

In a survey distributed to members of the Society of Obstetric Anesthesia and Perinatology (SOAP), almost one-third of 169 respondents required preoperative pregnancy testing for all childbearing-age female patients through mandatory departmental or institutional policy. Of the anesthesiologists surveyed, however, 66% required testing only when history indicated possible pregnancy. When surveyed, members of the ASA were asked whether pregnancy testing should be done routinely for all patients versus in select populations; 17% believed it was a necessary routine test, whereas 78% chose the latter. The finding of a positive result has a very important impact on clinical management because it could lead to either delays or cancellations of surgery. ^{, ,}

EVIDENCE

Several studies have been conducted to examine the reliability of a preoperatively obtained medical history to indicate the possibility of pregnancy ( Table 8.1 ). These studies included patients from different age groups. One study by Malviya and colleagues in the adolescent population showed that none of the patients who underwent testing were found to have a positive urine pregnancy test. Data from the study indicated that most of these patients denied the possibility of pregnancy, whereas very few were not sure. The authors concluded that a detailed history should be obtained in all postmenarchal patients, and unless indicated by that history, pregnancy testing would not be required. It is noteworthy that 17 patients in that study refused testing.

Alternatively, several other studies demonstrated that the medical history was often inconclusive and occasionally misleading. This was true for both adults and adolescents. Two studies, by Assam and colleagues and Pierre and colleagues, ⁹ demonstrated positive pregnancy test results in adolescent patients undergoing surgery with incidence rates of 1.2% and 0.49%, respectively. Notably, the medical history in the Pierre study did not always correlate with test results. More recently, Gong et al. reported an extremely low incidence of undetected pregnancies found on the day of surgery by urine testing, but many of the patients included in the study who were suspected of being pregnant were given the opportunity to self-test before scheduling their surgery.

Three additional studies included patients from all age groups. ^{, ,} Manley and colleagues, using either serum or urinary human chorionic gonadotropin (hCG), tested 2056 females undergoing ambulatory surgery. There was an incidence of 0.3% of unrecognized pregnancies. Wheeler and Cote tested 261 patients, ages 10 to 34 years, all of whom denied the possibility of pregnancy. Three patients (1.3%) had positive tests. Two of them were adults. Interestingly, the authors in the studies by both Azzam and colleagues and Wheeler and Cote point out that, although positive results were documented in teenagers, no positive result was detected in patients younger than 15 years of age. In a study on adolescents, Hennrikus and colleagues tested 532 females between ages 12 and 19. They found five patients to have positive urine hCG results; the youngest was 13 years of age. Furthermore, two additional retrospective reviews by Douglas et al. and Herr et al. found similar rates of unexpected positive pregnancy tests of 0.6% (n = 5477) and 0.5% (n = 410), respectively.

Evidence was most compelling in the adult population in the study done by Twersky and Singleton, which examined 315 consecutive females of childbearing potential undergoing elective surgery. Seven patients (2.2%) tested positive for serum beta-hCG. None of them were teenagers. The highest percentage of positive pregnancy tests was found among patients undergoing laparoscopic sterilization. A study done in the United Kingdom included 125 patients undergoing laparoscopic sterilization, of whom 6 had positive pregnancy tests (5%). The authors did not specify if the history of these patients indicated the possibility of being pregnant.