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Abnormal Triple Screen & AFPFrom: prenatal@dis.on.caWed Mar 5 10:43:59 1997
The short question might be "does a screen positive report in prenatal screening indicate a higher than average risk of fetal demise?" and the answer is Yes. "Even in a normal karyotype fetus?" Yes again, to a lesser extent, particularly when accompanied by low amniotic fluid volume. In response to the question of how to manage such a patient, it's my observation that the local geneticists here tend to proceed just as you have, with a level II ultrasound and counseling on amniocentesis. However, the nature of the "abnormal trisomy screen" is important in assessing this patient. Clearly, and as Allan Bombard has indicated, an elevated AFP is consistent with a threatened or recent fetal demise. The fact that the "trisomy screen" was still "abnormal" means that the other markers were substantially atypical as well, since a high AFP would diminish the calculated risk of fetal trisomy. Hence the questions arise: What is the patient's age? Since age is a factor in calculating a patient's risk of fetal trisomy, an older age patient would require less of an "abnormality" in her screening markers to trigger a screen positive report. This is important because the degree of abnormality of the individual markers is what's important in assessing the likelihood of fetal demise. Was this a "triple screen" (AFP, estriol and hCG)? Estriol is the earliest, and in that sense the most sensitive, indicator of threatened fetal demise, and a low estriol might have been the cause of the high calculated risk of fetal trisomy (either trisomy 21 or 18). What were the actual marker levels in MoMs? Much information lies buried in the individual marker levels, and reporting a screen as "positive" limits the chance of further assessment when fetal trisomy has been rulled out. Was the screen positive for risk of trisomy 21 or trisomy 18? hCG is more often low than high in fetal demise, depending on when the sample is taken relative to the demise. A low hCG is also associated with a HIGH risk of fetal trisomy 18, whereas it indicates a LOW risk of trisomy 21. Therefore a screen that was positive for risk of trisomy 18 would be consistent with threatened fetal demise - BUT the high AFP would preclude most programs from screening this patient positive for trisomy 18 UNLESS they're using the latest algorithm for risk calculation of trisomy 18. I have also seen cases of fetal demise with a moderate elevation in hCG accompanied by a very low estriol and an elevated AFP, and I would guess that this is the pattern in your patient. Don't forget that simply over-estimating the gestational age by a week or more might be enough to cause such a pattern, and give a report of screen positive for trisomy 21 - even in a patient with a high MSAFP. Andrew MacRae, Ph.D., FCACB Oshawa, Ontario, CANADA
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