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Limb defects after chorionic villus sampling
Although we appreciate Rossavik’s point about potential biases involving second trimester ultrasounds, the point does not seem to apply in this case. Mary L. Hediger, I’hD Theresa 0. Scholl, I’hD, MPH Joan I. Schall, I’hD Richard L. Fischer, MD Dqv~ut~cvzt
of Chktrk
U~iaersity
LIMB
of Mdiciw
& G~/rwco/ogy
mzd Dcrdistuy of Nrw /uwy -SOM
DEFECTS
VILLUS
AFTER
CHORIONIC
SAMPLING
The recent paper by Hsieh et al (~BSIET GYNECOL lYY5;85:84-8) raises yet another serious concern about the safety of chorionic villus sampling (CVS). However, if read carefully, it provides an excellent example that even an invasive diagnostic procedure, which by itself can be regarded as safe in experienced hands, can do considerable harm and damage to a patient’s health if it is carried out by inexperienced investigators. Furthermore, it raises numerous questions about various aspects of the methods of ascertainment that need to be clarified. Hsieh et al collected and reported on 1362 CVS procedures done by 67 centers in Taiwan. Dividing the number of casesequally among these centers would mean that each center did an average of only 20 CVS procedures during 1 year, far below the recommended number of 200-250.’ The fact that so few cabesof C‘VS had been reported to the authors during 1991raisesthe possibility of an ascertainment bias in the selection of answering centers. Thus, it would be interesting to know how many CVS procedures are done in the country during a year by the other centers. Furthermore, it is difficult to believe that during 3 years, only one infant with a limb reduction defect (the other cases listed are not limb reduction defects by the definition of such anomalies) in a population not exyowd to CVS was born in the whole country. Given the birth rate of 78,742 one would expect 3Y cases of limb reduction defects in this cohort of an unexposed population, if compared with large population-based studies in various countries.‘,’ Another question regarding the ,rscertainment of casesafter CVS exposure must be raised: As described by Hsieh et al, thesecaseswere collected retrospectively by the obstetricians up to 18 months postpartum. How reliably cm any obstetrician recall the degree of a skeletal defect in a newborn? 1 htl authors further me11VOI..
85,
NO.
h, JUNE
I++‘?
tlon that the patients were evaluated by photographic documentation. However, it is not stated how many patients had this kind of documentation available and how many were described only from memory. If 33 of 78,742 caseswere found in the total group, this gives a rate of 0.042X, not O.U32%as calculated by Hsirh et al. How can this difference be explained? Yet another question is, why were four of the eight fetuses with limb defects in the group exposed to CVS excluded from further analysis? We \cere unable to find an answer to this question in the paper. The authors write that 78,742 newborns \\ts~t‘ delivered in 3991 in the 67 hospitals chosen for this study. During the same time interval, 13b2 casesof CVS were performed in these hospitals. It would be interesting to know how many of the 78,742 caseshad a CVS done. Coming back to the fact that, of eight caseswith limb anomalies, only four were clwsen tar statistics in the paper, it might be reasonable to conclude that an unknown number of patients did have CVS outside of these 67 centers. Knowing this number of caseswould be very important, in that it might result in a completely different denominator and thus a completely different risk estimattt. Without knowledge of the total sample size, a calculation of any incidence of limb defects after CVS appears to be very arbitrary and might give a false impreshlon of actual risks.
We have good reason to believe that there were probably no significant deviations from the general population. The obstetric units responding to the survey were mostly hospitals that had large numbers of deliveries and possibly had more chance to see limb defects after CVS. However, for studying the incidence of limb deiects after CVS, we used the number of CVS procedures performed at the surveyed hospital as the L&ters
1063
of Chktrk
U~iaersity
LIMB
of Mdiciw
& G~/rwco/ogy
mzd Dcrdistuy of Nrw /uwy -SOM
DEFECTS
VILLUS
AFTER
CHORIONIC
SAMPLING
The recent paper by Hsieh et al (~BSIET GYNECOL lYY5;85:84-8) raises yet another serious concern about the safety of chorionic villus sampling (CVS). However, if read carefully, it provides an excellent example that even an invasive diagnostic procedure, which by itself can be regarded as safe in experienced hands, can do considerable harm and damage to a patient’s health if it is carried out by inexperienced investigators. Furthermore, it raises numerous questions about various aspects of the methods of ascertainment that need to be clarified. Hsieh et al collected and reported on 1362 CVS procedures done by 67 centers in Taiwan. Dividing the number of casesequally among these centers would mean that each center did an average of only 20 CVS procedures during 1 year, far below the recommended number of 200-250.’ The fact that so few cabesof C‘VS had been reported to the authors during 1991raisesthe possibility of an ascertainment bias in the selection of answering centers. Thus, it would be interesting to know how many CVS procedures are done in the country during a year by the other centers. Furthermore, it is difficult to believe that during 3 years, only one infant with a limb reduction defect (the other cases listed are not limb reduction defects by the definition of such anomalies) in a population not exyowd to CVS was born in the whole country. Given the birth rate of 78,742 one would expect 3Y cases of limb reduction defects in this cohort of an unexposed population, if compared with large population-based studies in various countries.‘,’ Another question regarding the ,rscertainment of casesafter CVS exposure must be raised: As described by Hsieh et al, thesecaseswere collected retrospectively by the obstetricians up to 18 months postpartum. How reliably cm any obstetrician recall the degree of a skeletal defect in a newborn? 1 htl authors further me11VOI..
85,
NO.
h, JUNE
I++‘?
tlon that the patients were evaluated by photographic documentation. However, it is not stated how many patients had this kind of documentation available and how many were described only from memory. If 33 of 78,742 caseswere found in the total group, this gives a rate of 0.042X, not O.U32%as calculated by Hsirh et al. How can this difference be explained? Yet another question is, why were four of the eight fetuses with limb defects in the group exposed to CVS excluded from further analysis? We \cere unable to find an answer to this question in the paper. The authors write that 78,742 newborns \\ts~t‘ delivered in 3991 in the 67 hospitals chosen for this study. During the same time interval, 13b2 casesof CVS were performed in these hospitals. It would be interesting to know how many of the 78,742 caseshad a CVS done. Coming back to the fact that, of eight caseswith limb anomalies, only four were clwsen tar statistics in the paper, it might be reasonable to conclude that an unknown number of patients did have CVS outside of these 67 centers. Knowing this number of caseswould be very important, in that it might result in a completely different denominator and thus a completely different risk estimattt. Without knowledge of the total sample size, a calculation of any incidence of limb defects after CVS appears to be very arbitrary and might give a false impreshlon of actual risks.
We have good reason to believe that there were probably no significant deviations from the general population. The obstetric units responding to the survey were mostly hospitals that had large numbers of deliveries and possibly had more chance to see limb defects after CVS. However, for studying the incidence of limb deiects after CVS, we used the number of CVS procedures performed at the surveyed hospital as the L&ters
1063