Confined placental mosaicism in CVS and pregnancy outcome

The role of confined placental mosaicism in fetal growth restriction: A retrospective cohort study

OBJECTIVE

To evaluate which cytogenetic characteristics of confined placental mosaicism (CPM) detected in the first trimester chorionic villi and/or placentas in terms of chromosome aberration, cell lineage involved and trisomy origin will lead to fetal growth restriction and low birthweight.

METHODS

Cohort study using routinely collected perinatal data and cytogenetic data of non-invasive prenatal testing, the first trimester chorionic villi sampling and postnatal placentas.

RESULTS

215 CPM cases were found. Fetal growth restriction (FGR) and low birthweight below the 10th percentile (BW < p10) were seen in 34.0% and 23.1%, respectively. Excluding cases of trisomy 16, 29.1% showed FGR and 17.9% had a BW < p10. The highest rate of FGR and BW < p10 was found in CPM type 3, but differences with type 1 and 2 were not significant. FGR and BW < p10 were significantly more often observed in cases with meiotic trisomies.

CONCLUSION

There is an association between CPM and FGR and BW < p10. This association is not restricted to trisomy 16, neither to CPM type 3, nor to CPM involving a meiotic trisomy. Pregnancies with all CPM types and origins should be considered to be at increased risk of FGR and low BW < p10. A close prenatal fetal monitoring is indicated in all cases of CPM.

Confined placental mosaicism: placental size and function evaluated on magnetic resonance imaging

OBJECTIVES

Evidence regarding placental function in pregnancies complicated by confined placental mosaicism (CPM) is conflicting. We aimed to compare placental function between CPM and non-CPM pregnancies prenatally and at birth. A secondary objective was to evaluate the relationship between placental function and chromosomal subtype of CPM.

METHODS

This was a retrospective study of pregnancies with CPM and control pregnancies delivered at a tertiary hospital in Denmark between 2014 and 2017. Placental volume and placental transverse relaxation time (T2*) were estimated on magnetic resonance imaging (MRI), fetal weight and uterine artery pulsatility index (UtA-PI) were estimated on ultrasound and fetoplacental ratio was assessed on MRI and at birth. These estimates of placental function were adjusted for gestational age and compared between groups using the Wilcoxon rank-sum test. Within the group of CPM pregnancies, measures of placental function were compared between those at high risk (chromosome numbers 2, 3, 7, 13 and 16) and those at low risk (chromosome numbers 5, 18 and 45X).

RESULTS

A total of 90 pregnancies were included, of which 12 had CPM and 78 were controls. MRI and ultrasound examinations were performed at a median gestational age of 32.6 weeks (interquartile range, 24.7-35.3 weeks). On MRI assessment, CPM placentae were characterized by a lower placental T2* Z-score (P = 0.004), a lower fetoplacental ratio (P = 0.03) and a higher UtA-PI Z-score (P = 0.03), compared with non-CPM placentae. At birth, the fetoplacental ratio was significantly lower (P = 0.02) and placental weight Z-score was higher (P = 0.01) in CPM pregnancies compared with non-CPM pregnancies. High-risk CPM pregnancies showed a reduced placental T2* Z-score (P = 0.003), lower birth-weight Z-score (P = 0.041), earlier gestational age at delivery (P = 0.019) and higher UtA-PI Z-score (P = 0.028) compared with low-risk CPM pregnancies. Low-risk CPM pregnancies did not differ in any of these parameters from non-CPM pregnancies.

CONCLUSIONS

CPM pregnancies are characterized by an enlarged and dysfunctional placenta. Placental function was highly related to the chromosomal type of CPM; placental dysfunction was seen predominantly in high-risk CPM pregnancies in which chromosomes 2, 3, 7, 13 or 16 were involved. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Pregnancy outcome of confined placental mosaicism: meta-analysis of cohort studies

OBJECTIVE

This study aimed to assess the rate of adverse obstetrical and neonatal outcomes in pregnancies diagnosed with confined placental mosaicism relative to that of unaffected controls.

DATA SOURCES

Web-based databases were searched using relevant key words, and articles published from 1980 to February 2022 were retrieved.

STUDY ELIGIBILITY CRITERIA

Observational studies in English language including ≥10 cases of singleton pregnancies with diagnosis of confined placental mosaicism were included. The diagnosis was established after detection of any chromosomal abnormality at chorionic villus sampling for any indication, followed by normal karyotype from amniotic fluid or neonatal leukocyte culture.

METHODS

Two authors independently screened the references for eligibility, data extraction, and assessment of methodological quality using the Newcastle-Ottawa scale. All available obstetrical and neonatal outcomes were recorded. Random-effect meta-analysis was performed to estimate pooled odds ratios and 95% confidence intervals of available outcomes in pregnancies with and without confined placental mosaicism. Statistical heterogeneity was evaluated with I2 statistics (International Prospective Register of Systematic Reviews registration number: CRD42021260319).

RESULTS

Of the 80 articles reviewed, 8 retrospective matched-cohort studies (708 cases of confined placental mosaicism and 11,599 unaffected controls) compared cases with and without confined placental mosaicism and were included in the meta-analysis. The risk of delivering small-for-gestational-age neonates was significantly increased in confined placental mosaicism pregnancies according to crude analysis (odds ratio, 2.45; 95% confidence interval, 1.23-4.89; I2=72%) and to sensitivity analysis of high-quality studies (odds ratio, 3.65; 95% confidence interval, 2.43-5.57; I2=0%). Similarly, confined placental mosaicism resulted in an increased risk of birthweight below the third centile (odds ratio, 5.33; 95% confidence interval, 1.19-24.19; I2= 83%). Subgroup analysis revealed that the risk of delivering small-for-gestational-age neonates was 3-fold higher for confined placental mosaicism excluding trisomy 16, and 11-fold higher for cases including trisomy 16 only vs unaffected controls, respectively. No difference was found in the risk of low birthweight and preterm birth (at <37 weeks' gestation). Other outcomes were insufficiently reported, therefore they were not analyzed.

CONCLUSION

Pregnant women prenatally diagnosed with confined placental mosaicism have an increased risk of impaired fetal growth, suggesting the need for intensified antenatal surveillance.

Confined placental mosaicism and the association with pregnancy outcome and fetal growth: a review of the literature

BACKGROUND

Chromosomal mosaicism can be detected in different stages of early life: in cleavage stage embryos, in blastocysts and biopsied cells from blastocysts during preimplantation genetic testing for aneuploidies (PGT-A) and later during prenatal testing, as well as after birth in cord blood. Mosaicism at all different stages can be associated with adverse pregnancy outcomes. There is an onward discussion about whether blastocysts diagnosed as chromosomally mosaic by PGT-A should be considered safe for transfer. An accurate diagnosis of mosaicism remains technically challenging and the fate of abnormal cells within an embryo remains largely unknown. However, if aneuploid cells persist in the extraembryonic tissues, they can give rise to confined placental mosaicism (CPM). Non-invasive prenatal testing (NIPT) uses cell-free (cf) DNA released from the placenta in maternal blood, facilitating the detection of CPM. In literature, conflicting evidence is found about whether CPM is associated with fetal growth restriction (FGR) and/or other pregnancy outcomes. This makes counselling for patients by clinicians challenging and more knowledge is needed for clinical decision and policy making.

OBJECTIVE AND RATIONALE

The objective of this review is to evaluate the association between CPM and prenatal growth and adverse pregnancy outcomes. All relevant literature has been reviewed in order to achieve an overview on merged results exploring the relation between CPM and FGR and other adverse pregnancy outcomes.

SEARCH METHODS

The following Medical Subject Headings (MESH) terms and all their synonyms were used: placental, trophoblast, cytotrophoblast, mosaicism, trisomy, fetal growth, birth weight, small for gestational age and fetal development. A search in Embase, PubMed, Medline Ovid, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL) and Google Scholar databases was conducted. Relevant articles published until 16 July 2020 were critically analyzed and discussed.

OUTCOMES

There were 823 articles found and screened based on their title/abstract. From these, 213 articles were selected and full text versions were obtained for a second selection, after which 70 publications were included and 328 cases (fetuses) were analyzed. For CPM in eight different chromosomes (of the total 14 analyzed), there was sufficient evidence that birth weight was often below the 5th percentile of fetal growth standards. FGR was reported in 71.7% of CPM cases and preterm birth (<37 weeks of delivery) was reported in 31.0% of cases. A high rate of structural fetal anomalies, 24.2%, in cases with CPM was also identified. High levels of mosaicism in CVS and presence of uniparental disomy (UPD) were significantly associated with adverse pregnancy outcomes.

WIDER IMPLICATIONS

Based on the literature, the advice to clinicians is to monitor fetal growth intensively from first trimester onwards in case of CPM, especially when chromosome 2, 3, 7, 13, 15, 16 and 22 are involved. In addition to this, it is advised to examine the fetuses thoroughly for structural fetal anomalies and raise awareness of a higher chance of (possibly extreme) premature birth. Despite prematurity in nearly a fifth of cases, the long-term follow-up of CPM life borns seems to be positive. More understanding of the biological mechanisms behind CPM will help in prioritizing embryos for transfer after the detection of mosaicism in embryos through PGT-A.

Rare autosomal trisomies: comparison of detection through cell-free DNA analysis and direct chromosome preparation of chorionic villus samples

OBJECTIVE

Direct chromosome preparations of chorionic villus samples (CVS) and cell-free DNA (cfDNA) testing both involve analysis of the trophoblastic cell lineage. The aim of this study was to compare the spectrum of rare autosomal trisomies (RATs) detected by these two approaches and assess the available information on their clinical significance.

METHODS

Data from 10 reports on genome-wide cfDNA testing were pooled to determine which chromosomes were most frequently involved in RAT-positive cases, and pregnancy outcome information was reviewed. CVS information was obtained from an updated database of 76 102 consecutive CVS analyses performed over a period of 18 years at TOMA laboratory, in which trophoblastic and mesenchymal layers were analyzed and amniotic fluid cell analysis was recommended for RAT-positive cases. Chromosomes involved and presence of confined placental mosaicism, true fetal mosaicism and uniparental disomy (UPD) for imprinted chromosomes were assessed. Also evaluated were the frequency and types of RATs in products of conception.

RESULTS

RATs were present in 634 of 196 662 (0.32%) cfDNA samples and 237 of 57 539 (0.41%) CVS trophoblast samples (P < 0.01). The frequency of RATs varied over 8-fold between the cfDNA reports. Confirmation of abnormality through amniocentesis was more likely when RATs were ascertained through cfDNA (14 of 151; 9.3%) than through CVS trophoblasts (seven of 237; 3.0%) (P < 0.01). In cfDNA-ascertained cases, trisomies 15, 16 and 22, which are associated with fetal loss, were identified proportionately more often. Of 151 cases with RAT identified by cfDNA and outcome information available, 41.1% resulted in normal live birth; 27.2% in fetal loss; 7.3% had phenotypic abnormality detected through ultrasound or other follow-up evaluation; 2.0% had a clinically significant UPD; and 14.6% had fetal growth restriction or low birth weight. All autosomes were involved in trisomies in products of conception; the most common RATs detected were trisomies 16, 22 and 15 with a frequency of > 9% each.

CONCLUSIONS

Although there are strong parallels between RATs ascertained through cfDNA analysis and direct chromosome preparation of CVS, caution is needed in applying conclusions from CVS analysis to cfDNA testing, and vice versa. RATs identified through genome-wide cfDNA tests have uncertain risks for fetal loss, growth restriction or fetal abnormality. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Outcomes in pregnancies with a confined placental mosaicism and implications for prenatal screening using cell-free DNA

PURPOSE

To assess the association between confined placental mosaicism (CPM) and adverse pregnancy outcome.

METHODS

A retrospective cohort study was carried out evaluating the outcome of pregnancies with and without CPM involving a rare autosomal trisomy (RAT) or tetraploidy. Birthweight, gestational age at delivery, fetal growth restriction (FGR), Apgar score, neonatal intensive care admission, preterm delivery, and hypertensive disorders of pregnancy were considered.

RESULTS

Overall 181 pregnancies with CPM and 757 controls were recruited. Outcome information was available for 69% of cases (n = 124) and 62% of controls (n = 468). CPM involving trisomy 16 (T16) was associated with increased incidence of birthweight <3rd centile (P = 0.007, odds ratio [OR] = 11.2, 95% confidence interval [CI] = 2.7-47.1) and preterm delivery (P = 0.029, OR = 10.2, 95% CI = 1.9-54.7). For the other RATs, an association with prenatally diagnosed FGR was not supported by birthweight data and there were no other strong associations with adverse outcomes.

CONCLUSION

Excluding T16, the incidence of adverse pregnancy outcomes for pregnancies carrying a CPM is low. RATs can also be identified through genome-wide cell-free DNA screening. Because most of these will be attributable to CPMs, we conclude that this screening is of minimal benefit.

Confined placental mosaicism revisited: Impact on pregnancy characteristics and outcome

OBJECTIVES

We wanted to re-evaluate the influence of confined placental mosaicism subtypes (type 2 and type 3) on pregnancy characteristics and outcome.

MATERIAL AND METHODS

From July 2009 to December 2015, 5512 chorionic villus samplings were performed in our Fetal Medicine Center. Conventional karyotyping was performed after long-term and short-term cultured villi to define type 2 or type 3 confined placental mosaicisms. Karyotype after amniocentesis was performed to exclude true fetal mosaicism, when appropriate. Pregnancy characteristics and outcomes were collected and compared to a control population.

RESULTS

Thirty-six (0.65%) confined placental mosaicisms were observed (13 type 2 and 23 type 3). Nuchal translucency was not increased for type 2 and type 3 confined placental mosaicisms. Pregnancy characteristics and outcomes were comparable between type 2 confined placental mosaicisms and the control population. In type 3 confined placental mosaicisms, median first trimester serum pregnancy-associated plasma protein A was lower than for the control population (p<0.001), preterm births were noticed in 56% (p<0.001), small for gestational age newborns in 74% (p<0.001), and adverse pregnancy outcome was reported in 35% (p<0.01).

CONCLUSION

Although type 2 confined placental mosaicisms appeared to have no influence on pregnancy characteristics and outcome, type 3 confined placental mosaicisms were associated with low levels of first trimester serum pregnancy-associated plasma protein A, preterm birth, small for gestational age newborns, and adverse pregnancy outcomes.

Confined placental mosaicism at chorionic villous sampling: risk factors and pregnancy outcome

OBJECTIVE

This study aims to investigate the clinical relevance of confined placental mosaicism (CPM) detected at chorionic villous sampling (CVS) and to identify risk factors for this condition.

METHOD

Women diagnosed with CPM between January 2005 and December 2009 were identified. They were matched to women with unremarkable CVS in a 1 : 2 ratio by study period and contacted by phone for interview.

RESULTS

One hundred fifteen exposed and 230 unexposed women were selected. Baseline characteristics did not differ between the study groups apart from maternal body mass index, which is mildly higher in the CPM group (+0.6 kg/m(2), p = 0.047), and maternal age, which is higher in women with type III CPM (39.7 ± 2.6 vs 37.1 ± 3.2 years, p = 0.005). A higher frequency of gestational hypertension was observed in exposed women (10% vs 2%) (p = 0.003). Small for gestational age newborns were more frequent in women with type I CPM (15% vs 5%, p = 0.03). The incidence of other main complications of pregnancy (stillbirth, prematurity, preeclampsia and gestational diabetes mellitus) was similar. Neonatal complications and subsequent infant health and development did not also differ.

CONCLUSION

Women with the diagnosis of CPM at CVS can be generally reassured regarding the course of pregnancy and infant health and development.

Confined placental mosaicism and pregnancy outcome: a distinction needs to be made between types 2 and 3

OBJECTIVE

To study the influence of types 2 and 3 confined placental mosaicism (CPM) on pregnancy outcome.

METHOD

From 13 809 chorionic villus samplings (CVSs), karyotype after long-term cultured villi (LTC-villi) was systematically performed. Next, in case of suspicion of CPM, karyotype after short-term cultured villi (STC-villi) was established to define type 2 CPM (chromosomal abnormality limited to the mesenchymal core) or type 3 CPM (chromosomal abnormality found both in the cytotrophoblast and the mesenchymal core). Confirmatory amniocentesis was performed to exclude fetal mosaicism. Uniparental disomy (UPD) testing was carried out when the abnormal cell line involved chromosomes 5, 6, 7, 15 or 16.

RESULTS

Fifty-seven CPM cases were observed (57/13 809 = 0.41%) and of these, 37 were type 2 and 20 were type 3 CPM. Incidence of preterm infants, neonatal hypotrophy and adverse pregnancy outcome were comparable between patients in whom type 2 CPM was demonstrated and the control population. In contrast, for the type 3 CPM the incidence of these factors was higher than for the control population.

CONCLUSION

When a CPM is suspected, it appears essential to determine type, since type 2 has no effect on fetal development and type 3 is associated with preterm infants, low birth weight and adverse pregnancy outcome.

Prenatal diagnosis and genetic counseling for mosaic trisomy 13

Counseling parents of a fetus with trisomy 13 mosaicism remains difficult because of the phenotypic variability associated with the condition; some patients exhibit the typical phenotype of complete trisomy 13 with neonatal death, while others have few dysmorphic features and prolonged survival. This article provides a comprehensive review of the prenatal diagnosis and genetic counseling for mosaic trisomy 13, including confined placental mosaicism 13, mosaic trisomy 13 diagnosed at amniocentesis, and phylloid hypomelanosis in association with mosaic trisomy 13.

Variable outcomes in mosaic trisomy 16: five case reports and literature analysis

OBJECTIVES

To report five cases of mosaic trisomy 16 with variable outcomes in the context of the literature on mosaic trisomy 16. Complications in these cases include preeclampsia, IUGR, fetal anomalies, and death, with no predictable pattern.

METHODS

Observation of five new cases and statistical analysis of 125 reported cases of mosaic trisomy 16 with prenatal detection and outcome data.

RESULTS

(1) IUGR, premature delivery, and/or physical anomalies are observed commonly, even when the trisomy is thought to be confined to the placenta; (2) Level II mosaicism for trisomy 16 in amniotic fluid may reflect a true mosaic state with phenotypic consequences; (3) FISH is more sensitive than traditional cytogenetics in detecting mosaicism in all tissue types examined; (4) hCG levels can be extremely elevated, and MS-AFP levels are often elevated; and (5) Uniparental disomy (UPD) increases the rates of IUGR and physical anomalies in CPM cases.

CONCLUSION

While there is no obvious mosaic trisomy 16 syndrome, IUGR and heart defects commonly occur, even if the mosaicism appears to be confined to the placenta. A completely normal outcome occurs only in about 20% of the cases; however, complications can often be limited to prematurity, small-for-gestational-age infants, and/or minor or surgically reparable birth defects.

Health and developmental outcome of children following prenatal diagnosis of confined placental mosaicism

OBJECTIVE

To determine the long-term health and development of a cohort of children in whom confined placental mosaicism (CPM) was diagnosed at prenatal diagnosis.

METHODS

A retrospective cohort study was performed comparing 36 children in whom CPM had been diagnosed prenatally with 195 controls subjects in whom a normal karyotype had been detected prenatally. Data comprising birth information, health, health service utilisation, growth, development, behaviour, and the family were collected by a maternal questionnaire administered when the subjects were aged between 4 and 11 years.

RESULTS

CPM cases did not differ from controls across a broad range of health measures and there were no major health problems or birth defects among the CPM group. No increase was detected in the incidence of intrauterine growth retardation (IUGR) among CPM cases; however, postnatal growth was reduced compared with controls (p = 0.047). Development and behaviour in CPM cases was similar to that of controls.

CONCLUSIONS

The prenatal diagnosis of CPM is not associated with an increased risk of birth defects or developmental problems, but may be associated with decreased growth.

Severe intrauterine growth restriction and trisomy 15 confined placental mosaicism: a case report and review of literature

OBJECTIVES

To correlate confined placental mosaicism (CPM) for trisomy 15 with severe intrauterine growth restriction (IUGR) and early death after birth (age of 6 months).

METHODS

Chromosome analysis was performed on amniotic fluid at 21st week of gestation, on peripheral blood at birth and on fibroblasts at death using conventional techniques. FISH was performed with Chromoprobe I-Multiprobe System kit and commercial probes according to manufacturer's protocol. DNA was extracted from parental and child peripheral blood, placenta tissue and skin fibroblasts, and UPD tests were done with microsatellites selected from Genome Data Base.

RESULTS

The child presented severe hypospadias, micropenis, bilateral cryptorchidism and bifid scrotum, inguinal hernia, dolichomegacolon, severe thymic lymphatic depletion and heart hypertrophy, mainly involving right ventricle. Mosaic trisomy 15 (84%) was discovered by FISH on placental biopsy at term. Uniparental disomy (UPD) for chromosome 15 was excluded. Prenatal (amniotic fluid), postnatal (peripheral blood) karyotypes and analysis on skin fibroblast metaphases were normal. Since the autopsy showed some features suggesting genetic syndromes, such as CATCH22, Williams-Beuren syndrome, matUPD2, we excluded the presence of all these diseases.

CONCLUSIONS

The only explanation for this clinical case seems to be the presence of tris15CPM that is reported as one of IUGR causes.

Mosaic trisomy 16 ascertained through amniocentesis: evaluation of 11 new cases

Trisomy 16, once thought to result uniformly in early pregnancy loss, has been detected in chorionic villus samples (CVS) from on-going pregnancies and was initially ascribed to a second, nonviable pregnancy. Prenatally detected trisomy 16 in CVS and its resolution to disomy has led to the reexamination of the viability of trisomy 16. This study evaluates 11 cases of mosaic trisomy 16 detected through second trimester amniocentesis. In 9 of the 11 cases, amniocenteses were performed in women under the age of 35 because of abnormal levels of maternal serum alpha-fetoprotein (MSAFP) or maternal serum human chorionic gonadotropin (MShCG). The other two amniocenteses were performed for advanced maternal age. Five of the 11 pregnancies resulted in liveborn infants, and six pregnancies were electively terminated. The liveborn infants all had some combination of intrauterine growth retardation (IUGR), congenital heart defects (CHD), or minor anomalies. Two of them died neonatally because of complications of severe congenital heart defects. The three surviving children have variable growth retardation, developmental delay, congenital anomalies, and/or minor anomalies. In the terminated pregnancies, the four fetuses evaluated by ultrasound or autopsy demonstrated various congenital anomalies and/or IUGR. Cytogenetic and fluorescent in situ hybridization studies identified true mosaicism in 5 of 10 cases examined, although the abnormal cell line was never seen in more than 1% of cultured lymphocytes. Placental mosaicism was seen in all placentas examined and was associated with IUGR in four of seven cases. Maternal uniparental disomy was identified in three cases. Mosaic trisomy 16 detected through amniocentesis is not a benign finding but associated with a high risk of abnormal outcome, most commonly IUGR, CHD, developmental delay, and minor anomalies. The various outcomes may reflect the diversity of mechanisms involved in the resolution of this abnormality. As 80% of these patients were ascertained because of the presence of abnormal levels of MSAFP or MShCG, the increased use of maternal serum screening should bring more such cases to clinical attention.

Trisomy 13 mosaicism at prenatal diagnosis: dilemmas in interpretation

We describe six cases of trisomy 13 mosaicism detected at prenatal diagnosis. Most level I and level II trisomy 13 mosaicism detected at prenatal diagnosis is pseudomosaicism or confined placental mosaicism. Rarely, low-level mosaicism at chorionic villus sampling or amniocentesis reflects a true fetal mosaicism. In this case, a normal phenotype is a possible, but not a certain, outcome. Genetic counselling is not straightforward.

Incidence and outcome of chromosomal mosaicism found at the time of chorionic villus sampling

OBJECTIVE

Chromosomal mosaicism has been reported in about 1% to 3% of chorionic villus sampling specimens. This report provides incidence and outcome information that should be useful in counseling patients found to have mosaicism on chorionic villus sampling.

STUDY DESIGN

A retrospective analysis of 11,200 consecutive patients undergoing chorionic villus sampling at the University of California, San Francisco, during the period from Jan. 1, 1984, to June 1, 1996, was undertaken.

RESULTS

A total of 140 cases of mosaicism were identified for an incidence of 1.3%. Follow-up information was available for 130 cases, 26 of which (20%) were confirmed in fetal tissue. Confirmation rates for specific types of mosaicism were as follows: autosomal trisomy 7.6%, sex chromosome 25%, structural abnormality 27.3%, and marker chromosome 77.8%. Neonatal outcome was normal in all cases for which pregnancy continued.

CONCLUSION

The data indicate that in most cases of chromosomal mosaicism found by chorionic villus sampling the mosaicism is unlikely to be clinically significant in the fetus.

Molecular-cytogenetic investigations of ten term placentae in cases of prenatally diagnosed mosaicism

Discrepant chromosome findings in the placenta and fetus are detected by additional investigations commonly after chorionic villus sampling (CVS) and occasionally after amniotic fluid cell cultures. In this paper we present the results of molecular-cytogenetic investigations (fluorescence in situ hybridization, FISH) of ten term placentae after prenatally detected mosaicism. In three cases, mosaicism was found after first-trimester CVS and in seven cases, after second-trimester amniotic fluid culture. All three results after CVS represented confined placental mosaicism (CPM). Two of the seven mosaic findings after amniocentesis were not confirmed postnatally. In the remaining five cases, general mosaicism was found. The analyses of six defined areas of the term placentae showed that it is important to investigate the placenta at multiple sites. The frequency of a cell line varied by more than 50 per cent at different analysed sites. FISH on interphase nuclei proved to be a rapid and reliable method of investigating large numbers of biopsies and cells per biopsy.

Case report: uniparental disomy 16 in association with congenital heart disease

Uniparental disomy (UPD) is the inheritance of both copies of a given chromosome from the same parent (Warburton, 1988; Anon., 1991). The exact disease associations of UPD of individual chromosomes have yet to be fully elucidated and the question of whether UPD of some chromosomes may be regarded as a benign finding remains unanswered. We report an infant with uniparental maternal disomy 16, the only such infant identified at King's College Hospital. The infant had intrauterine growth retardation and minor congenital heart disease.

Confined placental mosaicism for trisomies 2, 3, 7, 8, 9, 16, and 22: their incidence, likely origins, and mechanisms for cell lineage compartmentalization

Analysis of confined placental mosaicism (CPM) for trisomies 2, 3, 7, 8, 9, 16, and 22, in diagnostic chorionic villus sampling procedures, demonstrates apparent incidences of CPM for individual trisomies of between 9 and 91 cases per 100,000 pregnancies, with trisomy 7 being the most common. More detailed analysis of the percentage of aneuploid cells present, and the distribution of abnormality between the cytotrophoblast and extra-embryonic mesoderm cell lineages, shows a highly specific pattern for each chromosome. Theoretical considerations, in conjunction with direct observations, indicate that the overriding influence on the patterns of cell distribution seen in CPM is the distribution of aneuploid cells laid down during blastogenesis. This in turn reflects closely the origin of mosaicism from either correction of a trisomic conception or post-fertilization somatic error. The pattern of aneuploid cells for each trisomy, as seen at the end of the first trimester and later in pregnancy, can therefore be used to predict the relative contribution of meiotic and mitotic errors to CPM, and hence the likely incidences of uniparental disomy from this source, upd(16)mat being the most common (1 in 10,000 continuing pregnancies). In addition, CPM for trisomies 2, 3, and 8 shows strong evidence of a non-random distribution of aneuploid cells between the different extra-embryonic cell lineages. Analysis of comparable data from spontaneous abortion material repeats this non-random pattern for trisomies 2 and 3, and suggests that a similar phenomenon may also be occurring for trisomy 22. A non-random distribution could be attributable to selection for or against, or intolerance of, particular trisomic cells in certain lineages, but is more probably a result of either cell lineage-specific non-disjunction or consistent uneven compartmentalization of aneuploid cells during blastocyst development.

Risk of fetal mosaicism when placental mosaicism is diagnosed by chorionic villus sampling

OBJECTIVE

Our purpose was to determine the risk of fetal mosaicism when placental mosaicism is found on chorionic villus sampling.

STUDY DESIGN

We present a case of mosaic trisomy 22 detected on chorionic villus sampling and subsequently found in the fetus. A review of comprehensive chorionic villus sampling studies with emphasis on follow-up for fetal mosaicism was conducted.

RESULTS

Among 13 studies reviewed, 469 cases of placental mosaicism are presented; fetal mosaicism was found in 50 (10.7%). Factors associated with fetal mosaicism are (1) mosaicism on mesenchymal core culture and (2) type of chromosome abnormality involved--specifically, marker chromosomes (26.7%) and common autosomal trisomies (19.0%). Amniocentesis predicted fetal genotype in 93% to 100% of cases of placental mosaicism, depending on the cell type in which mosaicism was diagnosed.

CONCLUSIONS

Although mosaicism is usually confined to the placenta, the fetus is involved in about 10% cases. Patients should be counseled about this risk and the accuracy of follow-up amniocentesis.

Confined placental mosaicism in term placentae: analysis of 125 cases

In order to determine the incidence of confined placental mosaicism (CPM) in term placentae and to show the presence of specific sites and the effect on fetal development, 125 placentae from uneventful pregnancies were analysed by cytogenetic methods. The incidence was at least 4.8 per cent and there were no specific sites on the placenta. Although the number of cases is still too small, we found CPM to be associated with intrauterine growth retardation in six cases.

Trisomy 3 mosaicism on CVS: case report with literature review and propositions for investigation and counseling

Chorionic villus sampling performed for advanced maternal age revealed trisomy 3 in 20% of mitoses studied after a semi-direct chromosomal harvest. Amniocytes and cord blood showed a non-mosaic 46,XY karyotype. The birthweight of the normal newborn was at the tenth percentile. Analysis of term placenta by cytogenetics and by fluorescent in situ hybridization (FISH) confirmed the presence of the trisomy 3 in 20% and 12%, respectively, of cells from two peripheral placental biopsies. Placental histology was heterogeneous, some portions showing immature, edematous and undervascularized villi. DNA analysis confirmed the biparental origin of the chromosomes 3 in the child, whose development is normal at 36 months.