Discordance between prenatal cytogenetic diagnosis and outcome of pregnancy

The Foundation in Evidence of Medical and Dental Telephone Consultations

BACKGROUND

Patients can only make well-informed decisions if the information they are given by health professionals is based on scientific evidence. In this study, we assessed the foundation in evidence of free, publicly available telephone consultations in Germany.

METHODS

From March 2013 to January 2014, four hidden clients seeking information asked standardized questions about three medical topics (screening for colorectal cancer, for glaucoma, and for trisomy 21) and three dental ones (the sealing of dental fissures, professional dental cleaning, and mercury detoxification). Depending on the topic, the questions addressed such issues as the risk of disease and the purpose, content, validity, benefits, and risks of potential diagnostic and therapeutic measures. All identifiable telephone consultation services that provided counselling on the above topics were included in the study (23 government-sponsored institutions, 31 institutions independently run by physicians, 521 institutions under religious auspices, 25 dental counselling services).

RESULTS

Of the 599 telephone consultation services that were identified, 567 were contacted; 404 did not offer any relevant counselling. A total of 293 conversations were held with the remaining 163 consultation services. Six of these conversations fully met predefined criteria for evidence-based counselling. The percentage of appropriate answers to the key questions on each topic was 5% for colorectal cancer screening (7/140), 23.8% for glaucoma screening (25/105), 33.9% for trisomy 21 screening (121/357), 27.5% for the sealing of dental fissures (28/102), 16.2% for professional dental cleaning (19/117), and 12.9% for mercury detoxification (12/93). The percentage of appropriate answers also varied depending on the type of institution: 26.8% for government-sponsored institutions (67/250), 4.5% for institutions independently run by physicians (4/88), and 31.1% for institutions under religious auspices (82/264).

CONCLUSION

The medical and dental counselling now offered over the telephone by the types of institutions included in this study does not satisfy the criteria for evidence-based health information.

Errors in prenatal diagnosis

Prenatal screening and diagnosis are integral to antenatal care worldwide. Prospective parents are offered screening for common fetal chromosomal and structural congenital malformations. In most developed countries, prenatal screening is routinely offered in a package that includes ultrasound scan of the fetus and the assay in maternal blood of biochemical markers of aneuploidy. Mistakes can arise at any point of the care pathway for fetal screening and diagnosis, and may involve individual or corporate systemic or latent errors. Special clinical circumstances, such as maternal size, fetal position, and multiple pregnancy, contribute to the complexities of prenatal diagnosis and to the chance of error. Clinical interventions may lead to adverse outcomes not caused by operator error. In this review I discuss the scope of the errors in prenatal diagnosis, and highlight strategies for their prevention and diagnosis, as well as identify areas for further research and study to enhance patient safety.

False negative cytogenetic results following amniocentesis

We report 2 cases where prenatal cytogenetic studies following amniocentesis yielded false negative results. Both mothers requested termination of pregnancy but were reassured by the normal chromosome analysis and therefore continued their pregnancies. When cytogenetic studies were repeated in the neonatal period, they demonstrated chromosomal abnormalities, which were confirmed when the initial specimens from amniocentesis were reviewed. Because of our findings, we suggest that if prenatal chromosome analysis is reported as normal, where there is a high index of suspicion of a chromosome abnormality, the result should be questioned and neonatal chromosome analysis undertaken.

Cytogenetic analysis of 2928 CVS samples and 1075 amniocenteses from randomized studies

We report cytogenetic results from a randomized Danish chorionic villus sampling (CVS) and amniocentesis (AC) study including 2928 placental and 1075 amniotic fluid specimens processed in the same laboratory. The results are presented in groups comparing CVS with amniocentesis and transabdominal (TA) CVS with transcervical (TC) CVS as randomized. More abnormalities and more ambiguous diagnostic problems were found in placental tissues than in amniotic cells. There were no diagnostic errors and no incorrect sex predictions. Mosaicism was detected in 1 per cent of all cases of CVS (discordancies included). When confirmation studies were done, 90 per cent were found to be confined to the placenta. Eight cases (0.7 per cent) of mosaicism/pseudomosaicism were seen in amniotic fluid specimens, and two cases of five with confirmation studies were confirmed in the fetus. The rate of mosaicism/pseudomosaicism in CVS and AC specimens differed (p < 0.05). The rate of pseudomosaicism in cultures of villi and amniotic fluid cells was 0.5 and 0.6 per cent, respectively. Single-cell aneuploidy was observed in 1.8 per cent of villi and 1.4 per cent of amniotic fluid cell specimens. Maternal cell contamination (MCC) was seen more often after TC sampling (4.5 per cent) compared with TA sampling (1.5 per cent), but posed no problems in interpretation. Compared with the processing of cultured specimens, the short-term method of preparation of villi in our laboratory doubled the technicians' workload. For practical and economic reasons we have ceased the routine use of short-term preparations.

The European collaborative study on mosaicism in chorionic villus sampling: data from 1986 to 1987

Data on a total of 11,855 diagnostic chorionic villus samples obtained in the years 1986 and 1987 were compiled from a questionnaire filled in by 36 European cytogenetic centres. Mosaicism was reported in 141 cases. The cytogenetic findings were followed by induced abortion in 24 cases. Spontaneous abortion was observed in nine mosaic pregnancies, a rate not significantly different from that observed for CVS in total. Mosaicism was found in 1.2 per cent of analyses by direct analysis/short-term culture, in contrast to the 0.6 per cent found after long-term culture. Evidence for fetal non-mosaicism was found in 99 of the 141 cases. The finding of mosaicism in first-trimester CVS should always elicit further analyses, preferably after amniocentesis, to substantiate the suspected fetal chromosome aberration.

Validity of cytogenetic analyses from trophoblast tissue throughout gestation

Cytogenetic findings in the Münster Chorionic Villi Sampling (CVS) program are presented after 1,184 first trimester transcervical samplings and 131 second and third trimester placentacenteses. In the first trimester series the abnormality rate is low (2.4%) in patients with only an age-dependent aneuploidy risk. In this group terminations were performed in only 1.6% because of aneuploidy. True mosaicism was found more frequently after CVS, and the risk of maternal cell contamination seems higher as compared to amniocentesis. There are no obvious differences in the overall rate of diagnostic errors after both procedures, when metaphases after direct preparation and chorionic cell cultures are analysed and doubtful findings such as mosaicism are adequately followed up by amniocentesis. The cytogenetic techniques also offer a very rapid approach to karyotyping in the second and third trimester. We found a high rate of aneuploidy (15%) when placentacentesis was performed after sonographic diagnosis of fetal abnormalities. We conclude that cytogenetic analysis from trophoblast tissue is an accurate diagnostic tool applicable from first to third trimester of pregnancy.

Screening for Down's syndrome using an iso-risk curve based on maternal age and serum alpha-fetoprotein level

On the basis of the significantly different distributions of maternal serum alpha-fetoprotein (AFP) levels in 86 pregnancies associated with fetal Down's syndrome and in 2018 unaffected pregnancies, an iso-risk curve for Down's syndrome was constructed. An iso-risk curve shows, for women of all ages, which combinations of maternal age and level of maternal serum AFP result in the same risk of carrying a fetus with Down's syndrome. A 1:400 risk of Down's syndrome, corresponding to the risk of a 35-year-old woman, was chosen as the lowest risk indicating referral for amniocentesis. If all women, irrespective of their age, are offered amniocentesis, when their risk of carrying a Down's syndrome fetus is 1:400 or higher, 53% of the affected fetuses can be detected as compared with 28% of the affected fetuses diagnosed at present in women above 35 years of age.

Incidence of fetal chromosome abnormalities in 2264 low-risk women

Among a population of 6305 pregnant women, aged 25 to 34 years and estimated to be at no increased risk of genetic disease in the fetus, 4606 women participated in a randomized controlled trial of genetic amniocentesis between 1980 and 1984. In the study group having amniocentesis (2264 women), 23 fetal chromosome abnormalities (1.0 per cent) were found: eight autosomal aneuploidies, seven sex chromosome aneuploidies, seven balanced structural rearrangements and one case of a marker chromosome. The structural rearrangements and the marker chromosome were all shown to be inherited. The study group seemed representative for the whole population of younger women at low genetic risk. Therefore, a 1.0 per cent total rate of fetal chromosome abnormalities, consisting of one-third autosomal aneuploidies, one-third sex chromosome aneuploidies and one-third structural rearrangements, may be expected in the second trimester in younger low-risk women. In the same period of time, 562 women in the same age group were offered amniocentesis because of an estimated increased risk of fetal genetic disease. The total rate of fetal chromosome abnormality in this 'high-risk' group was 0.9 per cent and thus no different from the rate in the low-risk group.

The impact of prenatal diagnosis on the occurrence of chromosome abnormalities

From the public health point of view, several formal attempts have been made to measure the impact of prenatal diagnosis (PND) on the incidence of Down's Syndrome (DS), but the results have varied widely. The impact of PND (reduction in the birth rate of chromosomally abnormal neonates) is related to utilization rates but quantitative estimates of this have not been established. In a three-year (1981-1983) total population study from Queensland, Australia, we present results to measure the impact of a voluntary PND programme on the birth incidence of DS, and also other chromosomally abnormal births. Utilization rates for the PND service were 15.5 per cent in that population of mothers 35 years and over. Numbers and rates of all cases of chromosomal abnormalities are presented, subclassified by type of diagnosis--either by PND or by clinical diagnosis after birth. For the total population, 7.3 per cent of cases of DS were detected prenatally, and 15.4 per cent of all chromosome abnormalities. (A method for measuring the impact of PND is described.) Using this in conjunction with our demographic data, we estimate that with a 15 per cent utilization rate of PND by older mothers, 14 per cent of DS births can be prevented in this age group, or a 5 per cent overall reduction can be achieved if mothers of all ages are considered. One index--the ratio of the percentage of DS births which are preventable compared with the population utilization rates of PND--has potential for widespread use. Queensland data for this ratio is 0.34, a figure consistent with that from other studies. Thus a 3.5 per cent drop in the overall DS birth rate may be expected for each 10 per cent increase in the utilization rates of PND for mothers of 35 years and over. A diagram is presented which may serve as a model for improved data collection and better impact estimates in the future.

The use of amniotic FSH levels in resolving a discrepancy between fetal chromosomal and phenotypic sex

We report a case in which a discrepancy emerged between the prenatal diagnosis of female chromosomal sex and male sex at ultrasound examination. The FSH dosage performed on an amniotic fluid sample previously stored confirmed the male phenotype of the fetus. The effectiveness of the AF-FSH level dosage in prenatal diagnosis was taken into consideration.