Tuesday, January 3, 2012

Before You Kill That Bunny (A Few Thoughts on Pre-Operative Pregnancy Testing)


     This is my first public service announcement for 2012. The issue of routine pre-anesthetic pregnancy testing in women of child-bearing age who are scheduled for elective procedures seems to pop up again and again. Although routine pregnancy testing is not an American Society of Anesthesiologists (ASA) standard, the task force agreed that it should be considered for all women of childbearing age, especially in those patients with an "uncertain pregnancy history or a history suggestive of current pregnancy."(1) Despite this, and the data which demonstrate no convincing evidence that a single anesthetic has an adverse effect on a fetus (2), most of us still offer pregnancy testing to females who have a uterus and menstrual cycles. This includes any girl who has started having periods, which nowadays can be as young as eight or nine years of age.
     At my current institution, it is our policy to screen women of child-bearing age for pregnancy pre-operatively, and most of the time, it's not an issue. They've gone through pre-op clinic, and they either have a pregnancy test or documentation of a hysterectomy on the chart. Interestingly, we test a lot of women who've had tubal ligations, although I'm fairly certain the odds of spontaneous reversal of this form of sterilization are pretty low. Things start getting a little muddy when the patient didn't receive a pre-operative evalution or happens to be a same-day add on. In these situations, unless a girl hasn't yet reached menarche or a woman is menopausal or doesn't have a uterus, we are obliged to obtain a menstrual, and sexual history.
     The classic scenario is that the pre-op nurse informs you a patient is either on her period or completed it sometime within the last two weeks. For some reason, there is a public misconception that women cannot get pregnant when they are on their periods or breasfeeding. This couldn't be less accurate. Women can and do become pregnant during their cycles! The concept of "fertile periods" during the menstrual cycle was largely disproven in a 2000 NIH prospective cohort study. The data from that study revealed that in only 30% of women with regular cycles was the fertile period entirely within the menstrual cycle  (typically days 10-17). That means that 70% of women have fertile periods much earlier or much later in their cycles, and that in the majority of this population, ovulation is highly variable and unpredictable. The conclusion of this study was that there are "few days of the menstrual cycle during which some women are not potentially fertile."(3) This is why the rhythm method has such a high rate of failure in preventing pregnancy. Sperm can live for 3-5 days in the cervix, and since an estimated 2% of women are fertile by day 4 of their cycles, and 17% are fertile by day 7, it is conceivable that a woman who has intercourse during her period can become pregnant.(3) Therefore, in my opinion, if it is your policy to pregnancy test women pre-operatively, you should not exclude women who are within two weeks of their menstrual cycles, based on the assumption that they could not possibly be pregnant.  I have had at least two patients test positive for pregnancy before their elective cases, which the surgeons promptly cancelled. Regardless of whether it's a standard to test, pregnancy does change everything.  
     Another scenario is the woman who tells you, "Oh, there's no way I'm pregnant!" Well, if I'm your anesthesiologist, I want to know how you know that. I'm not being nosy or perverted. Unless you are completely sexually abstinent, meaning there hasn't been a penis within the vicinity of your vagina in several months, how do you know you're not pregnant? The "I have regular cycles" myth, addressed in the paragraph above, no longer holds water. With the exception of the IUD perhaps, the Pill and other forms of contraception are only as reliable as the person using it. If I'm able to assess that a woman is a decent historian and she tells me, "Girl, I haven't had sex in a year!" or "I'm a lesbian", then, that's good enough for me, and we can defer testing. In cases where a woman's spouse has had a vasectomy, I still feel compelled to offer a test. You'd be surprised at how many people cheat on their spouses, and I have been involved in some strange cases where marital infidelity leads to fractured penises and vaginal lacerations. We're all human beings, so I don't put anything past anybody, no matter how prim and proper the patient or family appears to be. Depravity isn't all that selective.  
     Most women don't seem to mind being offered a pregnancy test, but mothers of young girls who are menstruating can easily become offended: "What? You want to test my Madison?! Of course, she's not pregnant!" The nice thing about having an institutional policy on pre-anesthetic testing is that you can defer to it: "Your daughter is getting her period and we routinely pregnancy test females who have a uterus and are menstruating." Ba da-bing! Sadly, sometimes the only useful information young girls receive about sexuality and pregnancy is through their friends, the internet, or a pre-anesthetic evaluation. Like it or not, there are a lot of sexually active teenagers out there, even "A" students who are valedictorians! Unless you and your 15 year old daughter have an excellent relationship and extremely open communication about this subject, which from my observations is usually is not the case, doesn't it seem silly to assume she's not sexually active? A deeper issue is that sexual abuse does not discriminate, and even the most upright of families can have its share of unsavory skeletons in the closet. I've seen a lot of pregnant 11 and 12 year olds, so you are not likely to convince me that your daughter isn't worth consideration of a pre-anesthetic pregnancy test.
     In summary, the issue of pregnancy testing before elective anesthesia is one to be taken seriously. Aside from obtaining the patient's informed consent, we have to consider the implications of testing or not testing, and proceed with the understanding that a positive test will most likely change our management in some way. A quick, but thorough, menstrual and sexual history will generally provide clinicians with all the necessary information we require to make that decision. We're not passing moral judgment, we're simply collecting facts. Although many of us are uncomfortable discussing these subjects with our patients, we owe it to ourselves and them to do a better job of determining whether pregnancy testing is warranted before we administer an anesthetic.
    
ASA Practice Advisory for Preanesthetic Evaluation
Routine Pregnancy Testing Before Elective Anesthesia is Not an ASA Standard
The Timing of the Fertile Window in the Menstrual Cycle (NIH)

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