Amniocentesis
Abstract & Commentary
Synopsis: Serum testing of all pregnant women would reduce the number of amniocenteses and decrease procedure-related losses.
Source: Egan JF, et al. Obstet Gynecol 2000;96: 979-985.
Egan and colleagues reviewed u.s. birth data from the Centers for Disease Control and Prevention (CDC) between 1974-1997, during which time the rate of births to women 35 years or older rose from 4.7% of all deliveries to 12.6%. The practice of routinely offering triple screening (MSAFP, HCG, and estriol) to patients older than 35 years of age has not been uniformly embraced by practitioners and some official medical bodies. However, Egan et al calculated that if it were, and amniocentesis were only performed in those with a past triple screen risk of 1:250 or greater, 154,756 fewer amniocenteses would have been performed in 1997, and 733 procedure-related fetal losses would have been averted.
Comment by John C. Hobbins, MD
Counseling a patient of advanced maternal age can be extremely challenging for any provider, especially since the data on the efficacy of various noninvasive techniques seem to vary on a month-to-month basis. Genetic counseling should be available to all patients of advanced maternal age (AMA), but sadly often it is not because of negligible third-party reimbursement or lack of availability (which are undoubtedly inter-related). Years ago the threshold of age 35, above which one would offer invasive testing and below which one would not, was based on the concept that the risk of amniocentesis at that age was roughly equal to the risk of fetal Down syndrome. When the triple screen was introduced in 1988, it was deemed to be too inaccurate to be offered to patients at higher risk of aneuploidy. Since then, however, Haddow has shown it to be more than 80% sensitive in AMA patients.1
It is time to revamp the rules and put the decision making into the hands of the properly informed patient. To start with, there are a few givens:
• The risk of second trimester (15-20 weeks) amniocentesis is about one in 200, but could be as high as one in 100 (data from the only randomized trial in the literature).2
• Triple screen calculated risks for patients of AMA are legitimate.
Given these two variables, the patient can make up her mind regarding whether to take the next diagnostic step. As recently reported by Kupermann and colleagues, some patients may prefer to take a higher risk of amniocentesis than risk the chance of rearing a baby with Down syndrome, but others may opt out of amniocentesis, even when the scale is heavily tipped in the other direction.3 However, this should be the patient’s choice, and if the caregiver feels there is an unreasonable mismatch in either direction, he/she can refer the patient to someone else.
What is clear is that amniocentesis, in addition to having fetal risk, is expensive, costing generally more than $1000. At a time when there is an obsession over health care costs, $15 million could be saved by offering the above triple screen regimen to AMA patients. Perhaps some of these monies could then be put toward improved availability of genetic counseling.
Lastly, there is a growing body of information to suggest that a detailed ultrasound examination in the second trimester can work to adjust the risk for a given patient far more precisely than age alone, and there is further suggestion that ultrasound and triple screen testing can be used adjunctively for even better risk adjustment. This refinement will further allow amniocentesis to be performed in those who would benefit most from this procedure.
References
1. Haddow JE, et al. N Engl J Med 1992;327:588-593.
2. Tabor A, et al. Lancet 1986;1(8493):1287-1293.
3. Kupperman M, et al. Obstet Gynecol 2000;96:511-516.
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