First trimester chorionic villus sampling in twin gestations

Risk of fetal loss after chorionic villus sampling in twin pregnancy derived from propensity score matching analysis

OBJECTIVE

To estimate the risk of fetal loss associated with chorionic villus sampling (CVS) in twin pregnancy, using propensity score analysis.

METHODS

This was a multicenter cohort study of women with twin pregnancy undergoing ultrasound examination at 11-13 weeks' gestation, performed in eight fetal medicine units in which the leadership were trained at the Harris Birthright Research Centre for Fetal Medicine in London, UK, and in which the protocols for screening, invasive testing and pregnancy management are similar. The risk of death of at least one fetus was compared between pregnancies that had and those that did not have CVS, after propensity score matching (1:1 ratio). This procedure created two comparable groups by balancing the maternal and pregnancy characteristics that lead to CVS being performed, similar to how randomization operates in a randomized clinical trial.

RESULTS

The study population of 8581 twin pregnancies included 445 that had CVS. Death of one or two fetuses at any stage during pregnancy occurred in 11.5% (51/445) of pregnancies in the CVS group and in 6.3% (515/8136) in the non-CVS group (P < 0.001). The propensity score algorithm matched 258 cases that had CVS with 258 non-CVS cases; there was at least one fetal loss in 29 (11.2%) cases in the CVS group and in 35 (13.6%) cases in the matched non-CVS group (odds ratio (OR), 0.81; 95% CI, 0.48-1.35; P = 0.415). However, there was a significant interaction between the risk of fetal loss after CVS and the background risk of fetal loss; when the background risk was higher, the risk of fetal loss after CVS decreased (OR, 0.46; 95% CI, 0.23-0.90), while, in pregnancies with a lower background risk of fetal loss, the risk of fetal loss after CVS increased (OR, 2.45; 95% CI, 0.95-7.13). The effects were statistically significantly different (P-value of the interaction = 0.005). For a pregnancy in which the background risk of fetal loss was about 6% (the same as in our non-CVS population), there was no change in the risk of fetal loss after CVS, but, when the background risk was more than 6%, the posterior risk was paradoxically reduced, and when the background risk was less than 6%, the posterior risk increased exponentially; for example, if the background risk of fetal loss was 2.0%, the relative risk was 2.8 and the posterior risk was 5.6%.

CONCLUSION

In twin pregnancy, after accounting for the risk factors that lead to both CVS and spontaneous fetal loss and confining the analysis to pregnancies at lower prior risk, CVS seems to increase the risk of fetal loss by about 3.5% above the patient's background risk. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Fetal loss after chorionic villus sampling in twin pregnancy

OBJECTIVE

To estimate the chorionic villus sampling (CVS)-related risk of fetal loss in twin pregnancy after adjustment for chorionicity, nuchal translucency thickness (NT), intertwin discordance in crown-rump length (CRL), maternal demographic characteristics and serum pregnancy-associated plasma protein-A (PAPP-A) and free β-human chorionic gonadotropin (β-hCG).

METHODS

This was a multicenter study from eight fetal medicine units in which the leadership were trained at the Harris Birthright Research Centre for Fetal Medicine in London, UK, and in which the protocols for screening, invasive testing and pregnancy management are similar. Data were obtained prospectively from women with twin pregnancy undergoing routine ultrasound examination at 11-13 weeks' gestation. Multivariable logistic regression analysis with backward stepwise elimination was used to examine whether CVS provided a significant independent contribution to the prediction of risk of fetal loss after adjusting for maternal and pregnancy characteristics, including maternal age, racial origin and weight, method of conception, smoking status, parity, chorionicity, intertwin discordance in CRL, fetal NT ≥ 95^th percentile and free β-hCG and PAPP-A multiples of the median. Similarly, within the CVS group, multivariable logistic regression analysis was used to investigate the effect of the number of intrauterine needle insertions and size of the needle on the risk of fetal loss.

RESULTS

The study population of 8581 twin pregnancies undergoing ultrasound examination at 11-13 weeks' gestation included 316 dichorionic and 129 monochorionic twins that had CVS. First, in twin pregnancies undergoing CVS, compared to those not undergoing CVS, there was a 2-fold increased risk of fetal loss at < 24 weeks' gestation and of loss at any stage in pregnancy. Second, the factors providing a significant independent contribution to the prediction of miscarriage or fetal loss in twin pregnancy were increased maternal weight, black racial origin, monochorionicity, and more so monoamnionicity, large intertwin discordance in CRL and increased fetal NT, and, in the case of fetal loss at any stage, there was also a contribution from assisted conception and low serum PAPP-A. Third, after adjustment for maternal and pregnancy characteristics, CVS did not provide a significant contribution to the risk of fetal loss. Fourth, in twin pregnancies that had CVS, there was no significant contribution to fetal loss from the number of intrauterine needle insertions or needle size.

CONCLUSION

The 2-fold increased risk of fetal loss following CVS in twin pregnancy can, to a great extent, be explained by maternal and pregnancy characteristics rather than the invasive procedure itself. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Obstetrical outcomes after first-trimester chorionic villus sampling in twin pregnancies: A retrospective case-control study

AIM

Prenatal diagnostic testing by chorionic villus sampling (CVS) is sometimes recommended for women with twin pregnancies. However, few studies have compared the outcomes between twins with CVS and control twins without intervention. This study aimed to compare the obstetrical outcomes of CVS in twin pregnancies and those in non-intervention twin pregnancies.

METHODS

First-trimester transabdominal CVS was performed on dichorionic-diamniotic twins (n = 54; Group 1) between December 2006 and January 2017 at the Department of Obstetrics and Gynecology at our hospital, and the data were retrospectively analyzed. CVS risks were evaluated by comparing obstetrical outcomes with those of a control population of 155 dichorionic-diamniotic twins without intervention (Group 2).

RESULTS

The difference in the overall fetal loss rate (Group 1, 7.4% vs Group 2, 3.9%; P = 0.287) between the two groups was not statistically significant. The miscarriage rate, defined as delivery at <24 gestational weeks, and early preterm delivery, defined as delivery at <34 gestational weeks, were not significant between the groups (miscarriage: Group 1, 5.6% vs Group 2, 3.2%; P = 0.428; early preterm delivery: Group 1, 11.1% vs Group 2, 9.0%; P = 0.788). The mean gestational age at delivery, birth weights and neonatal intensive care unit admission rate were not statistically significant between the groups. Thus, the overall fetal loss rate and obstetrical outcomes of Group 1 were comparable with those of Group 2.

CONCLUSION

In conclusion, the overall obstetrical outcomes were not significantly different between twins with CVS and control twins with the advantage of enabling early decision-making about selective feticide in twins with CVS.

Trisomy 21 in both fetuses in a DCDA twin pregnancy

A woman's chances of having a child with Down syndrome increases with age. By age 40, the risk of conceiving a child with Down syndrome is about 1 in 100. We report a rare case of dizygotic dichorionic diamniotic twin pregnancy conceived via in vitro fertilisation, with both twins having trisomy 21. Both fetuses were independently detected to be at high risk of autosomal trisomy, initially via first-trimester screening and subsequently via invasive definitive diagnostic tests (ie, chorionic villus sampling and amniocentesis).Diagnosis of trisomy 21 has to be made via initial non-invasive prenatal screening, followed by further rigorous and accurate invasive pregnancy testing for confirmation. The gravity of the results necessitates high detection rates and high specificity of prenatal screening tests. Management of the patient must be multidisciplinary and supportive in nature, involving extensive and non-directive pregnancy counselling and management, genetic counselling and management of psychological distress.

Interventions et techniques de diagnostic prénatal visant l'obtention d'un prélèvement fœtal à des fins diagnostiques : Risques et avantages pour la mère et le fœtus

OBJECTIF

Offrir aux fournisseurs de soins de maternité et à leurs patientes des lignes directrices factuelles contemporaines en ce qui concerne les services de counseling traitant des risques et des avantages maternels propres à la tenue des interventions diagnostiques prénatales orientées par échographie (et/ou des techniques permettant l'établissement d'un diagnostic génétique) nécessaires dans les cas où il a été établi pendant la période prénatale que la grossesse serait exposée à des risques, ainsi qu'en ce qui concerne la prise de décisions subséquentes quant à la prise en charge de la grossesse (questions abordant des aspects tels que le niveau du fournisseur de soins obstétricaux, la surveillance prénatale, le lieu où devraient se dérouler les soins et l'accouchement, et la décision de poursuivre ou d'interrompre la grossesse). La présente directive clinique se limite aux services de counseling traitant des risques et des avantages maternels, et aux décisions en matière de prise en charge de la grossesse pour les femmes qui nécessitent (ou qui envisagent) la mise en œuvre d'une intervention ou d'une technique effractive orientée par échographie aux fins de l'établissement d'un diagnostic prénatal.

POPULATION DE PATIENTES

Femmes enceintes identifiées, à la suite de la mise en œuvre de protocoles établis de dépistage prénatal (taux sériques maternels ± imagerie, résultats d'analyse de l'ADN acellulaire indiquant des risques élevés, résultats anormaux au moment de l'imagerie fœtale diagnostique ou antécédents familiaux de troubles héréditaires), comme étant exposées à un risque accru d'anomalie génétique fœtale. Ces femmes pourraient nécessiter ou demander des services de counseling au sujet des risques et des avantages pour la grossesse de la tenue d'une intervention effractive orientée par échographie visant à déterminer l'étiologie, le diagnostic, et/ou la pathologie de possibles anomalies fœtales. RéSULTATS: La littérature publiée a été récupérée par l'intermédiaire de recherches menées dans Medline, PubMed et The Cochrane Library jusqu'en juin 2014 au moyen d'un vocabulaire contrôlé (« prenatal diagnosis », « amniocentesis », « chorionic villi sampling », « cordocentesis ») et de mots clés (« prenatal screening », « prenatal genetic counselling », « post-procedural pregnancy loss rate ») appropriés. Les résultats ont été restreints aux analyses systématiques, aux études observationnelles et aux essais comparatifs randomisés / essais cliniques comparatifs publiés en anglais entre janvier 1985 et juin 2014. Les recherches ont été mises à jour de façon régulière et intégrées à la directive clinique jusqu'en juin 2014. La littérature grise (non publiée) a été identifiée par l'intermédiaire de recherches menées dans les sites Web d'organismes s'intéressant à l'évaluation des technologies dans le domaine de la santé et d'organismes connexes, dans des collections de directives cliniques, dans des registres d'essais cliniques et auprès de sociétés de spécialité médicale nationales et internationales.

VALEURS

La qualité des résultats a été évaluée au moyen des critères décrits dans le rapport du Groupe d'étude canadien sur les soins de santé préventifs (Tableau 1). AVANTAGES, DéSAVANTAGES ET COûTS: Consentement éclairé de la patiente, transfert des connaissances, évaluation du risque génétique prénatal, soulagement de l'anxiété, création d'anxiété, défense des droits, compréhension du dépistage fœtal, limites du dépistage fœtal, choix en matière de prise en charge de la grossesse, complication de la grossesse ou fausse couche, soins opportuns et améliorés pour l'accouchement d'un enfant présentant une morbidité reconnue. RECOMMANDATIONS.

Pregnancy loss after chorionic villus sampling and genetic amniocentesis in twin pregnancies: a systematic review

OBJECTIVE

To review the available evidence regarding pregnancy loss following first-trimester chorionic villus sampling (CVS) and mid-trimester genetic amniocentesis in twins.

METHODS

We searched the MEDLINE database from January 1990 to May 2011 for randomized and cohort studies reporting on the risk of pregnancy loss after first-trimester CVS performed between 9 and 14 weeks and after genetic amniocentesis performed between 14 and 22 weeks. Where appropriate, we calculated pooled proportions and relative risks with 95% CI.

RESULTS

No randomized studies were found. For CVS, nine studies fulfilled the inclusion criteria. The overall pregnancy-loss rate was 3.84% (95% CI, 2.48-5.47; n = 4). The rate of pregnancy loss before 20 weeks was 2.75% (95% CI, 1.28-4.75; n = 3) and before 28 weeks was 3.44% (95% CI, 1.67-5.81; n = 3). For amniocentesis, the overall pregnancy-loss rate was 3.07% (95% CI, 1.83-4.61; n = 4). The rate of pregnancy loss before 20 weeks was 2.25% (95% CI, 1.23-3.57; n = 2), before 24 weeks was 2.54% (95% CI, 1.43-3.96; n = 9) and before 28 weeks was 1.70% (95% CI, 0.37-3.97; n = 5). Pooled data from four case-control studies showed a higher risk (2.59% vs. 1.53%) of pregnancy loss before 24 weeks following amniocentesis (relative risk = 1.81; 95% CI, 1.02-3.19). There were no statistically significant differences in reported pregnancy loss between transabdominal and transcervical approaches, use of a single-needle system vs. a double-needle system and single uterine entry vs. double uterine entry in the CVS group. Similarly, in the amniocentesis group, there was no statistically significant difference in fetal loss between the single uterine entry vs. the double uterine entry.

CONCLUSION

In the absence of randomized studies, it is not possible to estimate accurately the excess risk following invasive procedures in twins. Currently available data show similar overall pregnancy-loss rates for both amniocentesis and CVS with the excess risk of around 1% above the background risk.

Invasive Genetic Diagnosis in Multiple Pregnancies

Chromosomal anomalies and mendelian diseases are more frequent in multiple gestations than in singletons. Prenatal diagnosis is recommended in multiple pregnancies whenever indicated. Invasive testing using amniocentesis or chorionic villus sampling can be performed safely. Chorionic villus sampling has a significant advantage over amniocentesis because it offers rapid karyotyping and biochemical and DNA studies at an early stage of pregnancy. Only experienced centers should perform these procedures because of the technical aspects and the expertise needed in handling discordant results.

Prenatal diagnosis of Herlitz junctional epidermolysis bullosa in nonidentical twins

Advances in molecular diagnostics have led to the feasibility of DNA-based prenatal testing in families at risk for recurrence of severe forms of both dystrophic and junctional epidermolysis bullosa. In this report, we describe prenatal testing in a woman who previously had a child affected with Herlitz junctional epidermolysis bullosa. However, in her second pregnancy, she was found to have dichorionic diamniotic twins. DNA analysis of a pathogenic mutation and informative intragenic polymorphisms (LAMB3 gene) predicted one fetus to be affected and the other unaffected. Selective termination of the affected fetus was performed, and pregnancy with the unaffected fetus was continued, leading to full term delivery of a healthy girl with no skin blisters. This is the first reported case of DNA analysis in a twin pregnancy at risk of Herlitz junctional epidermolysis bullosa, with successful diagnosis and selective termination of one affected twin.

Invasive diagnostic procedures in twin pregnancies

The rising rate of multiple pregnancies and its association with advanced maternal age has expanded the need for prenatal diagnosis in twins and higher order gestations. The complexity of the invasive diagnostic procedures and the risk of loss of an unaffected twin raise significant clinical, technical and ethical issues. In this review we discuss the specific issues of early scanning, counseling and determination of chorionicity prior to invasive procedures in twins. We present the available data describing the risk associated with these procedures in twins and compare data of fetal loss rate from different studies. We also discuss the issues of fetal blood sampling and late karyotyping in twin pregnancies.

First-trimester fetal reduction to a singleton infant or twins: outcome in relation to the final number and karyotyping before reduction by transabdominal chorionic villus sampling

OBJECTIVE

The purpose of this study was to evaluate fetal outcome and maternal complications of multifetal pregnancy reduction to a single fetus or twins. To evaluate safety and efficacy of transabdominal chorionic villus sampling for karyotyping before fetal reduction.

STUDY DESIGN

Four hundred twenty-four consecutive multiple pregnancies were reduced to twins (255 pregnancies) or a single fetus (169 pregnancies) at 8 to 13 weeks of gestation after transabdominal chorionic villus sampling for fetal karyotyping. Fetal and maternal outcome were observed prospectively and compared with control series of twin (147) and singleton (885) pregnancies in which reduction procedures were not performed.

RESULTS

Transabdominal chorionic villus sampling was performed successfully in 100% of the cases. The accuracy of karyotyping was 99.2%. The overall pregnancy loss rate after reduction was 3.3%. No differences were observed between study and control series for severe prematurity, low birth weight, and neonatal deaths. Mean gestational age at delivery (35.2% vs 38.1%) and mean birth weight (2180 g vs 2873 g) were significantly lower; preterm delivery (64% vs 11%), neonatal death (3.4% vs 0.6%), and maternal complications (42.8% vs 9.5%) were significantly higher when the reduction was to twins rather than in reduction to a single fetus. Pregnancy loss rate did not differ between study series. The overall rate of chromosomal abnormalities in the study series was higher (relative risk, 2.0) than in singleton control series.

CONCLUSION

The outcome of multiple pregnancies that were reduced to a single fetus or twins was similar to that of nonreduced pregnancies; fetal and maternal complications were significantly lower in the series of pregnancies that were reduced to a single fetus. The safety and efficacy of transabdominal chorionic villus sampling and the higher pregnancy rate of chromosomal abnormalities in multiple pregnancies imply that fetal karyotyping should be advised before fetal reduction.

Invasive procedures in multiple gestations

PURPOSE OF REVIEW

The incidence of multiple gestations has increased significantly with advances in assisted reproductive techniques resulting in a concomitant increase in invasive procedures in these pregnancies. Commonly performed invasive procedures include amniocentesis, chorionic villus sampling, multifetal pregnancy reduction, and selective termination. Amniocentesis and chorionic villus sampling are also performed in singleton pregnancies, while multifetal pregnancy reduction and selective termination are procedures that are unique to multiple gestations.

RECENT FINDINGS

With increased operator experience, pregnancy loss rates after chorionic villus sampling, multifetal pregnancy reduction, and selective termination have decreased to acceptably low levels. Amniocentesis and chorionic villus sampling continue to have similar loss rates in experienced hands. A recent study suggests that amniocentesis in twins may have a higher post-procedural loss rate than in singletons; this may be due to the higher background loss rate of twins. There has been a recent increase in multifetal pregnancy reduction to a singleton with a trend towards improved outcomes over reduction to twins; future studies should focus on whether this confers a definitive advantage. Newer data suggests that selective termination after 20 weeks gestation in experienced hands does not increase loss rates over those procedures performed before 20 weeks. Newer techniques, such as cord coagulation, continue to be developed for selective termination in monochorionic pregnancies, though still with considerable morbidity and mortality.

SUMMARY

In summary, invasive procedures in multiple gestations are now commonly performed with. It is our hope that primary prevention of high order multiple pregnancies by optimization of assisted reproductive techniques will decrease the need for these procedures.

Prenatal genetic testing by amniocentesis appears to result in a lower risk of fetal loss than chorionic villus sampling in singleton pregnancies achieved by intracytoplasmic sperm injection

OBJECTIVE

To compare pregnancy outcome after prenatal genetic testing by chorionic villus sampling (CVS) or amniocentesis in singleton pregnancies achieved by intracytoplasmic sperm injection (ICSI).

DESIGN

Retrospective analysis.

SETTING

Tertiary referral center.

PATIENT(S)

Eight hundred twenty-eight patients with singleton gestations achieved by ICSI.

INTERVENTION(S)

Midtrimester amniocentesis (685 patients) and first-trimester CVS (143 patients).

MAIN OUTCOME MEASURE(S)

Fetal loss rate, preterm delivery rate, and proportion of babies born with low or very low birth weight.

RESULT(S)

A significant difference was observed in fetal loss rate between CVS and amniocentesis (3.7% vs. 0.9%, respectively). On the other hand, a similar preterm delivery rate was present between the two methods (11.2% vs. 12.4%, respectively). No significant difference was observed between amniocentesis and CVS in the proportion of babies with birth weight of either <1,500 g (1.8% vs. 3.8%, respectively) or between 1,500 and 2,500 g (8.2% vs. 4.6%, respectively).

CONCLUSION(S)

Amniocentesis appears to result in a lower risk of fetal loss as compared with CVS in patients with a singleton pregnancy achieved by ICSI.

Neonatal data on a cohort of 2889 infants born after ICSI (1991-1999) and of 2995 infants born after IVF (1983-1999)

BACKGROUND

To evaluate the safety of ICSI, this study compared data of IVF and ICSI children by collecting data on neonatal outcome and congenital malformations during pregnancy and at birth.

METHODS

The follow-up study included agreement to genetic counselling and eventual prenatal diagnosis, followed by a physical examination of the children after 2 months, after 1 year and after 2 years. 2840 ICSI children (1991-1999) and 2955 IVF children (1983-1999) were liveborn after replacement of fresh embryos. ICSI was carried out using ejaculated, epididymal or testicular sperm.

RESULTS

In the two cohorts, similar rates of multiple pregnancies were observed. ICSI and IVF maternal characteristics were comparable for medication taken during pregnancy, pregnancy duration and maternal educational level, whereas maternal age was higher in ICSI and a higher percentage of first pregnancies and first children born was observed in the ICSI mothers. Birthweight, number of neonatal complications, low birthweight, stillbirth rate and perinatal death rate were compared between the ICSI and the IVF groups and were similar for ICSI and IVF. Prematurity was slightly higher in the ICSI children (31.8%) than in the IVF children (29.3%). Very low birthweight was higher in the IVF pregnancies (5.7%) compared with ICSI pregnancies (4.4%). Major malformations (defined as those causing functional impairment or requiring surgical correction), were observed at birth in 3.4% of the ICSI liveborn children and in 3.8% of the IVF children (P = 0.538). Malformation rate in ICSI was not related to sperm origin or sperm quality. The number of stillbirths (born > or =20 weeks of pregnancy) was 1.69% in the ICSI group and 1.31% in the IVF group. Total malformation rate taking into account major malformations in stillborns, in terminations and in liveborns was 4.2% in ICSI and 4.6% in IVF (P = 0.482).

CONCLUSIONS

The comparison of ICSI and IVF children taking part in an identical follow-up study did not show any increased risk of major malformations and neonatal complications in the ICSI group.

Twin pregnancy: the role of ultrasound in management

Determination of chorionicity is one of the most important issues in the management of twin pregnancy. Modern ultrasound equipment has made it possible to accurately assess placentation already in the first trimester with the lambda sign. With regard to prenatal diagnosis, it is important to know the chorionicity in order to calculate the risk of chromosomally abnormal fetuses. Accurate chorionicity offers the obstetricians the opportunity to observe the monochorionic twins more intensively than is required for twins with dichorionic placentation. This review gives an update of the state of the art for clinicians caring for twin pregnancies.

Outcome of first-trimester chorionic villus sampling for genetic investigation in multiple pregnancy

OBJECTIVES

To evaluate the efficacy of and risk associated with chorionic villus sampling for genetic investigations in multiple pregnancies, and to evaluate the accuracy of the ultrasonographic detection of chorionicity during the first trimester.

PATIENTS AND METHODS

A total of 198 sets of twins and nine sets of triplets from 10 087 consecutive first-trimester pregnancies undergoing chorionic villus sampling were considered. Gestational age ranged from 7 to 12.6 weeks. Assessment and confirmation of chorionicity was based on a multiplicity of features. Dichorionicity was established in 169 sets of twins (85.3%) and trichorionicity in all triplet cases, while 29 twins were considered monochorionic. Chorionic villus sampling was performed transabdominally in all but one case, and identification of the placental insertion of the umbilical cord was the main benchmark for sampling. Sampling risks were evaluated by comparing clinical outcome with that of a control population of 63 dichorionic twin pregnancies which underwent no invasive procedure.

RESULTS

Determination of the presence or absence of the lambda sign led to a correct assignment of chorionicity in all cases, while the presence of a membrane thickness of 2 mm or more reflected a 100% specificity with a 22% false negative rate. Sampling was successfully performed in all cases and in only four cases (1.0%) were two needle insertions needed. At follow-up no evidence of incorrect sampling was reported. Karyotyping was provided to all patients, and in 94.1% of cases both short and long-term culture methods were carried out. No difference in fetal and perinatal losses between the study and control populations was found, but a higher rate of deliveries before 37 weeks and of low birth weight babies was noted amongst controls.

CONCLUSIONS

Chorionicity in twin pregnancy can be determined with certainty between 7 and 12 weeks of gestation; in cases of confluent placentas reliability is provided by determining the presence or absence of the lambda sign. This study indicates that first-trimester transabdominal chorionic villus sampling is a highly efficient, reliable, and relatively safe approach for genetic diagnosis in twin pregnancies. Although a precise evaluation of the relative risks of chorionic villus sampling and mid-trimester amniocentesis in twins must await randomized control studies, the advantages of a first-trimester diagnosis to enable early decision-making about selective fetal reduction are obvious.

Chorionic villus sampling before multifetal pregnancy reduction

OBJECTIVE

This study was undertaken to determine the technical feasibility and accuracy of chorionic villus sampling before multifetal pregnancy reduction and to determine whether sampling increases the pregnancy loss rate after the reduction procedure.

STUDY DESIGN

Between January 22, 1986, and January 20, 2000, a total of 1183 patients underwent first-trimester multifetal pregnancy reduction at Mount Sinai Medical Center. Chorionic villus sampling was attempted in 86 patients before the reduction procedure. Information on the technical success and accuracy of chorionic villus sampling, as well as pregnancy outcome, was collected on all patients. Pregnancy loss rates before 24 weeks' gestation in patients undergoing chorionic villus sampling before multifetal pregnancy reduction were compared with rates in patients not undergoing sampling.

RESULTS

Chorionic villus sampling was successfully completed in 85 (98.8%) of 86 patients in whom sampling was attempted. Of 166 fetuses, 165 (99.4%) were successfully sampled. Of 165 fetuses, 3 (1.8%) had karyotypic abnormalities. Sampling errors were probably made in 2 (1.2%) of 165 fetuses. Of the 73 patients who have been delivered or are beyond 24 weeks' gestation, only 1 patient (1.4%) had a pregnancy loss after the multifetal pregnancy reduction.

CONCLUSIONS

Chorionic villus sampling before multifetal pregnancy reduction is technically feasible and accurate, with an acceptably low sampling error rate. Chorionic villus sampling before multifetal pregnancy reduction appears to be safe and does not increase the risk of loss after the reduction procedure.

Prenatal diagnosis in multiple pregnancy

Fetal abnormality is more common in multiple than in singleton pregnancies. This, together with the requirement to consider the risks with at least two babies to sample correctly each fetus and to undertake accurately-targeted selective termination, amounts to a major challenge for obstetricians involved in prenatal diagnosis. Early determination of chorionicity should be routine, since this influences not only the genetic risks but also the invasive procedure chosen for karyotyping or genotyping. Assessment of nuchal translucency identifies individual fetuses at risk of trisomy. Contrary to expectation, invasive procedures in twins appear to have procedure-related miscarriage rates that are similar to those in singletons. Instead, contamination remains a concern at chorionic villus sampling. Elective late karyotyping of fetuses may have a role in some countries. Whereas management options for discordant fetal abnormality are relatively straightforward in dichorionic pregnancies, monochorionic pregnancies are at risk of co-twin sequelae after any single intrauterine death. Techniques have now been developed to occlude completely the cord vasculature by laser and/or ultrasound guided bipolar diathermy. Given the complexities associated with prenatal diagnosis, all invasive procedures in multiple pregnancies should be performed in tertiary referral centres.

Chorionic villus sampling in multiple pregnancies

OBJECTIVE

To evaluate the accuracy and risk of chorionic villus sampling (CVS) for prenatal diagnosis in multiple pregnancies.

METHOD

Twenty-eight chorionic villus samplings were carried out in a group of women with twin pregnancies. A transabdominal route was chosen in 24 samplings and the rest (four samplings) were carried out in a transcervical route. In the group of women with triple pregnancies, 14 tests were performed in a transabdominal route and one in a transcervical route.

RESULTS

No sampling failure occurred. One laboratory failure occurred in a triplet pregnancy, and one abnormal karyotype (47,xy+18) was found in the group of 28 twin fetuses. The rest of the fetuses in this group had normal karyotypes. Of the five triplets, two chromosomal abnormalities were diagnosed: a mosaic 46,xy/47,xxy was found in both cases. One fetus was affected by fragile -x syndrome. Selective reduction of the affected fetuses was carried out. There was no spontaneous fetal loss. Fetuses which were found to have normal prenatal tests were also found to be normal when born.

CONCLUSION

In this relatively small series of CVS in twins and triplets, the procedure has been proven to be safe and reliable for prenatal diagnosis.

Screening for fetal abnormalities in multiple pregnancies

Multiple gestations account for 1-2% of all pregnancies but contribute disproportionately to the incidence of both perinatal loss and fetal structural abnormalities. Ultrasound examination provides essential information about screening for, and the management of, such defects, including accurate determination of chorionicity, assessment of risk, invasive testing and selective termination if appropriate.