Prenatal Screening for and Diagnosis of Aneuploidy in Twin Pregnancies

ObjectiveTo provide a Canadian consensus document with recommendations on prenatal screening for and diagnosis of fetal aneuploidy (e.g., Down syndrome and trisomy 18) in twin pregnancies.OptionsThe process of prenatal screening and diagnosis in twin pregnancies is complex. This document reviews the options available to pregnant women and the challenges specific to screening and diagnosis in a twin pregnancyOutcomesClinicians will be better informed about the accuracy of different screening options in twin pregnancies and about techniques of invasive prenatal diagnosis in twins.EvidencePubMed and Cochrane Database were searched for relevant English and French language articles published between 1985 and 2010, using appropriate controlled vocabulary and key words (aneuploidy, Down syndrome, trisomy, prenatal screening, genetic health risk, genetic health surveillance, prenatal diagnosis, twin gestation). Results were restricted to systematic reviews, randomized controlled trials, and relevant observational studies. Searches were updated on a regular basis and incorporated in the guideline to August 2010. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology assessment-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies The previous Society of Obstetricians and Gynaecologists of Canada guidelines regarding prenatal screening were also reviewed in developing this clinical practice guideline.ValuesThe quality of evidence was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care (Table 1).Benefits, harms, and costsThere is a need for specific guidelines for prenatal screening and diagnosis in twins These guidelines should assist health care providers in the approach to this aspect of prenatal care of women with twin pregnancies.Summary StatementsFetal nuchal translucency combined with maternal age is an acceptable first trimester screening test for aneuploidies in twin pregnancies. (II-2)First trimester serum screening combined with nuchal translucency may be considered in twin pregnancies It provides some improvement over the performance of screening by nuchal translucency and maternal age by decreasing the false-positive rate. (II-3)Integrated screening with nuchal translucency plus first and second trimester serum screening is an option in twin pregnancies. Further prospective studies are required in this area, since it has not been validated in prospective studies in twins (III)Non-directive counselling is essential when invasive testing is offered (III)When chorionic villus sampling is performed in non-monochorionic multiple pregnancies, a combination of transabdominal and transcervical approaches or a transabdominal only approach appears to provide the best results to minimize the likelihood of sampling errors. (II-2)RecommendationsAll pregnant women in Canada, regardless of age, should be offered, through an informed counselling process, the option of a prenatal screening test for the most common clinically significant fetal aneuploidies. In addition, they should be offered a second trimester ultrasound for dating, assessment of fetal anatomy, and detection of multiples. (I-A)Counselling must be non-directive and must respect a woman's right to accept or decline any or all of the testing or options offered at any point in the process. (III-A)When non-invasive prenatal screening for aneuploidy is available, maternal age alone should not be an indication for invasive prenatal diagnosis in a twin pregnancy. (II-2A) If non-invasive prenatal screening is not available, invasive prenatal diagnosis in twins should be offered to women aged 35 and over. (II-2B)Chorionicity has a major impact on the prenatal screening process and should be determined by ultrasound in the first trimester of all twin pregnancies (II-2A)     

Strategies of antenatal diagnosis and management of pathologies related to multiple pregnancies

In the first trimester, ultrasound is crucial to screen for aneuploidies based on nuchal translucency, to diagnose major birth defects, and to establish chorionicity. Indeed prenatal diagnosis strategies as well as obstetrical management options are largely based on placental type. In the second trimester, maternal serum screening is not as effective, and ultrasound screening is more difficult in twins than in singletons. When a severe abnormality in found in one twin, selective termination of pregnancy may be considered. This technique is safe in dichorionic twins, but hazardous in monochorionic pregnancies. Selective termination in dichorionic twins is safer in the first trimester, underscoring the need for early prenatal diagnosis in twins. Monochorionic twin pregnancies carry specific risks, such as the twin-to-twin transfusion syndrome, which can be treated by endoscopic photo-coagulation of intertwin anastomoses in the severe early onset cases, or by amnioreduction in milder cases.     

Application of QF-PCR for the prenatal assessment of discordant monozygotic twins for fetal sex

OBJECTIVE: To establish the utility of quantitative fluorescent polymerase chain reaction (QF-PCR) in order to determine the zygosity of multiple pregnancies, as well as to define the origin of the most frequent aneuploidies in amniotic fluid samples. METHODS: We describe the case of a monochorionic (MC) diamniotic (DA) pregnancy with phenotypically discordant twins (nuchal cystic hygroma and non-immune hydrops in twin A and no anomalies in twin B). QF-PCR was performed for rapid prenatal diagnosis in uncultured amniocytes and subsequently in cultured cells. Polymorphic markers for chromosomes X, Y, 13, 18 and 21 were used for determination of zygosity as well as sex chromosome aneuploidy. RESULTS: Twin A showed a Turner Syndrome (TS) mosaicism pattern by QF-PCR in uncultured amniocytes. The monozygotic origin of the pregnancy was determined. Interphase fluorescence in situ hybridization (I-FISH) in this sample showed a mosaicism X0/XY (83/17%). Cytogenetic analysis revealed a 45,X0 karyotype in twin A and a 46,XY karyotype in twin B. CONCLUSIONS: QF-PCR is a reliable tool for the determination of the zygosity independently of the chorionicity and the fetal sex in case of twin pregnancy. Testing both direct and cultured cells can provide useful results for genetic counselling in chromosomal mosaicisms.     

Cribado cromosómico del primer trimestre. Resultados en gestaciones tras reproducción asistida

Objective

To determine the effectiveness of the combined test for aneuploidies in the first trimester of spontaneous pregnancies in comparison with pregnancies following assisted reproductive technology (ART).

Materials and methods

We performed a retrospective study of 1675 triple tests performed in the first trimester in our center, including pregnancy-associated plasma-A (PAPP-A) and the free fraction of the β subunit of human chorionic gonadotropin (free β-hCG), maternal age and nuchal scan. Of these, 1299 (77.5%) were spontaneous pregnancies and 376 (22.5%) were pregnancies following ART. The cut-off point for recommending an invasive test was 1/270.

Results

The combined test was carried out in 74 twin pregnancies, with two false-positive results. Among single pregnancies, 70 positive triple tests were obtained, 3.79% of spontaneous pregnancies and 6.84% of ART pregnancies. Eleven chromosomal abnormalities were found, nine in spontaneous pregnancies and two in ART pregnancies. The sensitivity of the test was 89% in spontaneous pregnancies and 100% in ART pregnancies. The specificity was 96% and 93.77%, respectively.

Conclusions

The first trimester triple test has high sensitivity and specificity in single pregnancies, whether spontaneous or following ART. The rate of positive triple tests is higher in pregnancies following ART.     

Impact of fetal sex in pregnancy-induced hypertension and preeclampsia in Japan

The male antigen (HY), the elevated level of fetal antigen in twin pregnancies, and the increased number of MHC mismatches in dizygotic twin pregnancies might affect immunological tolerance during pregnancy. Using the Perinatal Database of the Japanese Society for Obstetrics and Gynecology, we studied the occurrence of pregnancy-induced hypertension (PIH) and preeclampsia in mothers delivering singleton babies and in those delivering monochorionic diamniotic (MD) twin pregnancies and dichorionic diamniotic (DD) twin pregnancies at 125 centers of the perinatal network in Japan from 2001 through 2005. In singleton pregnancies, pregnant women carrying female fetuses had a significantly higher incidence of PIH and preeclampsia compared with those carrying male fetuses. In MD twin pregnancies, compared with mothers carrying male-male fetuses, those carrying female-female fetuses had significantly higher incidences of PIH and preeclampsia and a marked difference was observed in primiparous cases. In DD twin pregnancies, the incidences of PIH and preeclampsia were significantly higher in mothers with female-female fetuses than those with male-male fetuses, while those with male-female fetuses had intermediate values. The incidence of PIH and preeclampsia in MD twin pregnancies was similar to that in DD twin pregnancies with male-male fetuses or female-female fetuses. The male antigen and the increased number of MHC mismatches in DD twin pregnancies were not a risk factor for PIH and preeclampsia. Female fetal sex was a risk factor for PIH and preeclampsia.     

正常单胎及双胎妊娠妇女子宫动脉血流变化的比较

目的探讨正常单胎和双胎妊娠妇女子宫动脉血流搏动指数（ＰＩ）在孕期中的变化,并研究子宫动脉血流ＰＩ与胎盘位置的关系。方法采用Ｄｏｐｐｌｅｒ超声诊断仪,对９９例正常单胎妊娠和２４例正常双胎妊娠妇女的子宫动脉血流ＰＩ进行了检测,并同时探测胎盘的位置。结果单胎妊娠妇女的子宫动脉血流ＰＩ无论是胎盘侧或是对侧,均随孕周增加至分娩呈逐渐下降,孕２９周时子宫动脉血流ＰＩ平均值０．７８±０．１３。但双胎妊娠妇女的子宫动脉血流ＰＩ值随孕周逐渐下降至孕２７周后,则维持在一平台水平。孕２９周时子宫动脉血流ＰＩ平均值０．６７±０．１１,无论是单胎妊娠还是双胎妊娠,胎盘侧子宫动脉血流ＰＩ值均较对侧为低。结论单胎或双胎妊娠胎盘侧子宫动脉均较对侧血流丰富;且双胎妊娠时子宫动脉血流阻力较单胎为低。     

Maternal serum unconjugated oestriol and human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down's syndrome.

OBJECTIVE--To investigate maternal serum unconjugated oestriol (uE3) and human chorionic gonadotrophin (hCG) levels in twin pregnancies and to consider the implications of the results for antenatal screening for Down's syndrome. DESIGN--Measurement of maternal serum uE3 and hCG levels from 15-22 weeks of gestation in twin and singleton pregnancies. Previously available maternal serum alpha-fetoprotein (AFP) levels were also presented. SETTING--Stored serum samples collected from women receiving routine antenatal care in Oxford were used. SUBJECTS--200 women with a twin pregnancy and, for each, three singleton control pregnancies matched for gestational age (same completed week of pregnancy) and duration of storage of the serum sample (same calendar quarter). RESULTS--The median uE3, hCG and AFP levels in the twin pregnancies were respectively, 1.67 (95% CI 1.56-1.79), 1.84 (95% CI 1.64-2.07) and 2.13 (95% CI 1.97-2.31) multiples of the median (MoM) for singleton pregnancies at the same gestational age. The variance of values for the three serum markers (expressed in logarithms), and the correlation coefficients between any two, were similar in the twin and singleton pregnancies. CONCLUSION--In maternal serum screening programmes for Down's syndrome dividing uE3, hCG and AFP MoM values in twin pregnancies by the corresponding medians for twin pregnancies will, in expectation, yield a similar false-positive rate in twin pregnancies as in singleton pregnancies.     

Biparietal diameter growth in uncomplicated twin gestation

Ninety-six fetuses of uncomplicated concordant twin pregnancies were monitored by ultrasonic cephalometry from 13 to 38 weeks gestation. The biparietal diameter (BPD) growth of 96 twin fetuses was then compared to a sample of 299 uncomplicated, appropriate-for-gestational-age singleton pregnancies. Regression analysis applied to these measurements of BPD on twin and singleton pregnancies showed no significant difference in biparietal diameter between uncomplicated singleton and twin pregnancies. It is concluded that charts derived from singleton pregnancies may be reliably used for estimation of gestational age of twins.     

Amniotic fluid alpha-fetoprotein concentrations in twin gestations: dependence on placental membrane anatomy

Placental membrane anatomy was evaluated after delivery in 65 twin pregnancies undergoing genetic amniocentesis with amniotic fluid alpha-fetoprotein and acetylcholinesterase determinations when indicated. Each twin member in the 57 uncomplicated twin pregnancies was found to have an amniotic fluid alpha-fetoprotein concentration similar to that of singleton pregnancies of an equivalent gestational age. Eight twin pregnancies were found to be discordant for fetal anomalies associated with an elevated amniotic fluid alpha-fetoprotein and acetylcholinesterase level. The amniotic fluid alpha-fetoprotein concentration in the unaffected fetus in these eight cases was found to be dependent on placental membrane structure. Of the five discordant twin pregnancies with diamnionic-dichorionic placentas, all unaffected twins demonstrated an amniotic fluid alpha-fetoprotein concentration within the normal range for gestational age with a normal acetylcholinesterase level. In three twin pairs with diamnionic-monochorionic placentas, the unaffected twin member had significantly elevated amniotic fluid alpha-fetoprotein and acetylcholinesterase levels, which suggested diffusion of alpha-fetoprotein and acetylcholinesterase through the amnion-amnion interface.     

Ultrasonographic determination of chorion type in twin gestation

Reported are sonographic criteria for distinguishing the chorionic type of twin pregnancies prenatally. Thirty-four twin pregnancies were prospectively evaluated with correct assignment of chorionic type in 33 cases. The ability to determine the chorionic type of twin gestation facilitated the prenatal diagnosis and management in eight of the studied cases. Knowledge of the type of twinning antenatally is important in the management of twin pregnancies.     

Midtrimester maternal serum inhibin A levels after multifetal pregnancy reduction

OBJECTIVE: To investigate the relationship between the maternal serum inhibin A concentrations and the number of fetuses. Further, the maternal serum inhibin A levels for twin pregnancies and multiple pregnancies reduced to twins in the second trimester were compared. METHODS: Three groups of women with pregnancies following in vitro fertilization and embryo transfer were recruited for this study. Groups 1, 2 and 3 included 20 singleton pregnancies, 37 twin pregnancies, and 35 multifetal pregnancies, respectively. In group 3, multifetal reduction was performed during 10-12 weeks of gestation. Blood samples were obtained longitudinally at 10th, 12th, 15th and 18th week of gestation. RESULTS: There was a significant association between the number of fetuses and maternal plasma inhibin A prior to multifetal reduction. The inhibin A levels were not significantly different between twin and multifetal reduced twin pregnancies at 15th and 18th weeks of gestation. CONCLUSION: In multifetal reduction to twin pregnancies, the maternal serum levels of inhibin A decrease to the level of twin pregnancies during the second trimester. Therefore, inhibin A may be effectively used as a marker for Down syndrome screening in cases of twin pregnancy following multifetal reduction.     

双胎自发性早产预测及预防

随着辅助生殖技术的发展,双胎妊娠的发生率增加,早产的发生率也随之增加。有证据表明,超声检测宫颈长度和胎儿纤维蛋白测试可以预测双胎妊娠的自发性早产,但是到目前为止,没有任何有效的双胎妊娠的自发性早产的干预措施。本文对双胎自发性早产的预测和预防进行阐述。     

The amniotic fluid index in normal twin pregnancies

OBJECTIVE: We sought to investigate the amniotic fluid index for individual gestational sacs of twin pregnancies. STUDY DESIGN: Four hundred eighty-eight patients with normal diamniotic twins were examined between 14 and 40 weeks' gestation. The dividing membrane between twin fetuses was identified. An amniotic fluid index was then obtained for each gestational sac. RESULTS: The median amniotic fluid index in individual twin gestational sacs rises slowly from 14 to 16 weeks' gestation to 23 to 28 weeks' gestation and then gradually declines. The median amniotic fluid index values by gestational age for twin A and twin B are not statistically different. Although twin pregnancies have a slightly lower median amniotic fluid index value than singleton pregnancies, the difference is also not statistically significant. CONCLUSION: Individual amniotic fluid indices can be obtained in twin pregnancies, and the values are comparable with those of singleton gestations.     

Maternal risks and perinatal outcome in a Danish national cohort of 1005 twin pregnancies: the role of in vitro fertilization

BACKGROUND: Twin pregnancies constitute 25% of all in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) pregnancies. There is a lack of knowledge on maternal risks and perinatal outcome of IVF/ICSI twin pregnancies. METHODS: National survey by questionnaire (n = 1769). The study population consisted of all IVF/ICSI twin mothers (n = 266) and the two control groups of all IVF/ICSI singleton mothers (n = 764) and non-IVF/ICSI twin mothers (n = 739) who delivered in Denmark in 1997. The response rate was 89% among IVF twin mothers and overall 81%. RESULTS: In terms of maternal risks and perinatal outcome no significant differences were observed between IVF/ICSI twin and non-IVF/ICSI twin pregnancies after stratification for maternal age and parity. Nevertheless, IVF/ICSI twin mothers were more frequently on sick leave (OR 2.5, 95% CI 1.5-4.0) and hospitalized (OR 1.9, 95% CI 1.3-2.8) during pregnancy. Compared with IVF/ICSI singleton pregnancies, IVF/ICSI twin pregnancies were characterized by a higher incidence of preeclampsia (OR 2.4, 95% CI 1.5-4.2) and a higher frequency of sick leave (OR 6.8, 95% CI 4.4-10.5) and hospitalizations during pregnancy (OR 3.5, (95% CI 2.5-4.9); moreover, mean birthweight (p < 0.001) and gestational age (p < 0.001) were lower. No differences were observed in the incidence of pregnancy-induced hypertension and gestational diabetes between IVF/ICSI twin and singleton pregnancies. CONCLUSION: Although this population study indicates that maternal risks in IVF/ICSI twin pregnancies are comparable with non-IVF/ICSI twin pregnancies, the IVF/ICSI twin mothers were more likely to be on sick leave or hospitalized during pregnancy. Furthermore, maternal risks were higher and obstetric outcome poorer in IVF/ICSI twin vs. IVF/ICSI singleton pregnancies.     

IVF twins have similar obstetric and neonatal outcome as spontaneously conceived twins: a prospective follow-up study

Studies comparing the outcome of spontaneous versus IVF twin pregnancies report heterogeneous results. This may depend on differences in the studied populations and/or in the management approach to twin pregnancy. The aim of the present study was to compare both maternal and perinatal outcomes in dichorionic diamniotic twin pregnancies who where spontaneously conceived or originated by successful homologous IVF. In order to get homogeneous observations, monochorionic twin pregnancies and triplet pregnancies were excluded. Moreover, to avoid any possible bias deriving from differences in the obstetric management, all pregnancies were managed by the same team applying fixed obstetric protocols. The study included 223 twin pregnancies, 84 conceived by IVF and 139 spontaneously conceived. Overall, maternal and perinatal outcomes were similar in the two groups: no significant differences were observed as far as gestational age at delivery, birthweight, perinatal morbidity and mortality, and rate of malformations were concerned. The rate of Caesarean section was slightly, but not significantly, higher in IVF pregnancies. In conclusion, the outcome of IVF twin pregnancies is comparable to that of spontaneously conceived twin pregnancies, provided that the same management criteria are applied.     

Studies on changes in serum estrone, estradiol, estriol, DHA-S, and cortisol and urinary estriol excretion

Radioimmunoassay was used in order to investigate changes in steroid hormone, serum estrone, estradiol, estriol, dehydroepiandrosterone-sulfate (DHA-S) and cortisol in 71 cases of twin pregnancies. Also, urinary estriol was measured by the Amberlite XAD-2 method. These results were compared with those in 90 cases of single pregnancies. In the third trimester, the increase in serum estrogen levels in twin pregnancies was significantly higher than that in single pregnancies. From 28 to 34 weeks of pregnancy, the DHA-S level in single pregnancies rapidly dropped and after that, gradually decreased to the base level. But in the other weeks of pregnancy, no change in DHA-S was observed. The serum cortisol level in twin pregnancies was slightly higher than in single pregnancies. There was no significant difference between them. The nse in the cortisol level in twin pregnancies was significantly greater than in single pregnancies after 38 weeks of pregnancy. The urinary estriol level in twin pregnancies was significantly higher than in single pregnancies and had values 1.8-3.0 times higher than in single pregnancies.     

Rapid prenatal diagnosis of aneuploidies and zygosity in multiple pregnancies by amniocentesis with single insertion of the needle and quantitative fluorescent PCR

OBJECTIVE: To investigate amniotic fluid (AF) samples retrieved in multiple pregnancies by single insertion of the needle, for rapid assessment of chromosome copy number, zygosity, and cross-contamination between fetuses, using Quantitative Fluorescent Polymerase Chain Reaction (QF-PCR) amplification of highly polymorphic microsatellite markers. METHODS: Fifty-two multiple pregnancies were selected (47 twins, 5 triplets) and 108 samples of amniotic fluid were sampled between 12 to 20 weeks of gestation (mean 15.5) using the single-needle technique. Aneuploidy screening by QF-PCR amplification of short tandem repeats (STRs) on chromosomes X, Y, 21, 13, and 18 was carried out within 24 h of collection. Owing to the sampling procedure, the eventual presence of contamination between fetuses was also evaluated in every case. RESULTS: Normal and aneuploid fetuses were readily identified by QF-PCR. Fetal reduction was made available, for trisomic fetuses, without further waiting for completion of fetal karyotyping. In twin gestations, the ultrasound examination of chorionicity was always in agreement with the molecular assessment of zygosity. Contamination between fetuses due to the sampling procedure with a single puncture was never observed. CONCLUSION: Rapid prenatal diagnosis of aneuploidies by QF-PCR is a sensitive, efficient, and reliable assay. When applied in multiple pregnancies, it has the added value of allowing the assessment of zygosity in all cases, independently of chorionicity and fetal sex.     

Management of twin pregnancies discordant for anencephaly

Objective To examine options of management and outcome of twin pregnancies discordant for anencephaly.
Design Retrospective study.
Setting Research Centre for Fetal Medicine.
Population Twenty-four twin pregnancies discordant for anencephaly.
Methods A computer search was made of our database for twin pregnancies discordant for anencephaly. The data were reviewed for gestation at presentation, chorionicity, management and pregnancy outcome.
Main outcome measures Pregnancy outcome in relation to chorionicity and management.
Results There were 13 dichorionic and 11 monochorionic twin pregnancies discordant for anencephaly. In the dichorionic group five pregnancies had selective fetocide at 17 to 21 weeks; one pregnancy resulted in spontaneous abortion but in the others a healthy infant was born at a median gestation of 37 weeks. The other eight dichorionic pregnancies were managed expectantly, but three developed polyhydramios at 26 to 30 weeks; in one case amniodrainage was performed and in another selective fetocide was carried out. In this group the median gestation at delivery was 35 weeks. All 11 monochorionic pregnancies were managed expectantly and in three there was intrauterine death of both fetuses. In the other eight cases the normal twin was liveborn at a median gestation of 34 weeks; in four of these pregnancies polyhydramnios developed and two were managed by amniodrainage.
Conclusions In monochorionic pregnancies, expectant management is associated with a high rate of intrauterine lethality of the normal twin. In dichorionic pregnancies selective fetocide in the second trimester prevents the development of polyhydramnios and is associated with a lower risk of preterm delivery but can cause miscarriage.     

双胎妊娠子痫前期预防和处理

子痫前期（preeclamsia,PE）是妊娠期严重并发症,与母体及围产儿不良结局的发生有密切关系,是孕产妇严重并发症发生的主要原因。双胎妊娠并发子痫前期的发生率比单胎高3～4倍且双胎妊娠子痫前期发病更早,对孕产妇及围产儿造成的影响更大。文章根据双胎妊娠的临床特点,结合现有的妊娠期高血压疾病诊治指南及专家共识对双胎妊娠子痫前期预防和临床处理方案进行阐述。