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Pitfalls in assessing chorioamnionicity: novel observations and literature review

Published:February 17, 2018DOI:https://doi.org/10.1016/j.ajog.2018.02.010
      Accurate diagnosis of chorioamnionicity in multiple pregnancies is the key to appropriate clinical management of multiple gestation. Although prenatal ultrasound assessment of chorioamnionicity is well established and highly accurate if performed in early pregnancy, exceptions and artifacts arise from anatomic variations in multiple pregnancies and unusual sonographic features do exist. We have summarized our own experiences and reports from the literature on these pitfalls as follows: (1) discordant fetal sex in monochorionic pregnancies due to sex chromosome abnormalities, genital malformation in 1 fetus, or dizygotic twins forming a monochorionic placenta; (2) separate placental masses in monochorionic pregnancies due to bipartite placenta; (3) false-negative and false-positive λ sign can arise for various reasons, and in partial monochorionic/dichorionic placentas both T and λ sign may co-exist; (4) intrauterine synechia appearing as a thick and echogenic intrauterine septum may lead to erroneous diagnosis of dichorionic twins; and (5) errors in ascertaining amnionicity by the visualization of thin intertwin amniotic membranes and the number of yolk sacs. The ultrasound techniques to reduce inaccuracy in prenatal determination of chorioamnionicity and the use of single nucleotide polymorphisms based on noninvasive prenatal test to determine zygosity are also reviewed.

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      References

        • Templeton A.
        The multiple gestation epidemic: the role of the assisted reproductive technologies.
        Am J Obstet Gynecol. 2004; 190: 894-898
        • Kulkarni A.D.
        • Jamieson D.J.
        • Jones Jr., H.W.
        • et al.
        Fertility treatments and multiple births in the United States.
        N Engl J Med. 2013; 369: 2218-2225
        • Luke B.
        Pregnancy and birth outcomes in couples with infertility with and without assisted reproductive technology: with an emphasis on US population-based studies.
        Am J Obstet Gynecol. 2017; 217: 270-281
        • Aston K.I.
        • Peterson C.M.
        • Carrell D.T.
        Monozygotic twinning associated with assisted reproductive technologies: a review.
        Reproduction. 2008; 136: 377-386
        • Blickstein I.
        • Verhoeven H.C.
        • Keith L.G.
        Zygotic splitting after assisted reproduction.
        N Engl J Med. 1999; 340: 738-739
        • Blickstein I.
        Estimation of iatrogenic monozygotic twinning rate following assisted reproduction: pitfalls and caveats.
        Am J Obstet Gynecol. 2005; 192: 365-368
        • Vitthala S.
        • Gelbaya T.A.
        • Brison D.R.
        • Fitzgerald C.T.
        • Nardo L.G.
        The risk of monozygotic twins after assisted reproductive technology: a systematic review and meta-analysis.
        Hum Reprod Update. 2009; 15: 45-55
        • McNamara H.C.
        • Kane S.C.
        • Craig J.M.
        • Short R.V.
        • Umstad M.P.
        A review of the mechanisms and evidence for typical and atypical twinning.
        Am J Obstet Gynecol. 2016; 214: 172-191
        • Moise Jr., K.J.
        • Johnson A.
        There is NO diagnosis of twins.
        Am J Obstet Gynecol. 2010; 203: 1-2
        • Constantine S.
        • Wilkinson C.
        Double trouble: the importance of reporting chorionicity and amnionicity in twin pregnancy ultrasound reports.
        J Med Imaging Radiat Oncol. 2015; 59: 66-69
        • Carter E.B.
        • Bishop K.C.
        • Goetzinger K.R.
        • Tuuli M.G.
        • Cahill A.G.
        The impact of chorionicity on maternal pregnancy outcomes.
        Am J Obstet Gynecol. 2015; 213: 390.e1-390.e7
        • Luke B.
        • Gopal D.
        • Cabral H.
        • Stern J.E.
        • Diop H.
        Adverse pregnancy, birth, and infant outcomes in twins: effects of maternal fertility status and infant gender combinations; the Massachusetts outcomes study of assisted reproductive technology.
        Am J Obstet Gynecol. 2017; 217: 330.e1-330.e15
        • McLennan A.S.
        • Gyamfi-Bannerman C.
        • Ananth C.V.
        • et al.
        The role of maternal age in twin pregnancy outcomes.
        Am J Obstet Gynecol. 2017; 217: 80.e1-80.e8
        • Hubinont C.
        • Lewi L.
        • Bernard P.
        • Marbaix E.
        Anomalies of the placenta and umbilical cord in twin gestations.
        Am J Obstet Gynecol. 2015; 213: S91-S102
        • Norton M.E.
        • Chauhan S.P.
        • Dashe J.S.
        • Society for Maternal-Fetal Medicine
        Society for Maternal-Fetal Medicine (SMFM) clinical guideline 7: nonimmune hydrops fetalis.
        Am J Obstet Gynecol. 2015; 212: 127-139
        • Moldenhauer J.S.
        • Johnson M.P.
        Diagnosis and management of complicated monochorionic twins.
        Clin Obstet Gynecol. 2015; 58: 632-642
        • Dias T.
        • Contro E.
        • Thilaganathan B.
        • Khan H.
        • Zanardini C.
        • Mahsud-Dornan S.
        Pregnancy outcome of monochorionic twins: does amnionicity matter?.
        Twin Res Hum Genet. 2011; 14: 586-592
        • Sebire N.J.
        • Snijders R.J.
        • Hughes K.
        • Sepulveda W.
        • Nicolaides K.H.
        The hidden mortality of monochorionic twin pregnancies.
        Br J Obstet Gynaecol. 1997; 104: 1203-1207
        • Hack K.E.
        • Derks J.B.
        • Elias S.G.
        • et al.
        Increased perinatal mortality and morbidity in monochorionic versus dichorionic twin pregnancies: clinical implications of a large Dutch cohort study.
        BJOG. 2008; 115: 58-67
        • Unal E.R.
        Fetal surveillance and timing of delivery for multiples.
        Clin Obstet Gynecol. 2015; 58: 676-689
        • Machin G.
        Non-identical monozygotic twins, intermediate twin types, zygosity testing, and the non-random nature of monozygotic twinning: a review.
        Am J Med Genet C Semin Med Genet. 2009; 151C: 110-127
        • Bohec C.
        • Douet-Guilbert N.
        • Basinko A.
        • et al.
        Difficult diagnosis and management of an heterokaryotypic monochorionic twin pregnancy with discordant fetal sex and 45,X/47,XYY karyotypes.
        Fetal Pediatr Pathol. 2010; 29: 424-430
        • Shetty A.
        • Smith A.P.
        The sonographic diagnosis of chorionicity.
        Prenat Diagn. 2005; 25: 735-739
        • Finberg H.
        The “twin peak” sign: reliable evidence of dichorionic twinning.
        J Ultrasound Med. 1992; 11: 571-577
        • Lee Y.M.
        • Cleary-Goldman J.
        • Thaker H.M.
        • Simpson L.L.
        Antenatal sonographic prediction of twin chorionicity.
        Am J Obstet Gynecol. 2006; 195: 863-867
        • Morin L.
        • Lim K.
        Ultrasound in twin pregnancies.
        J Obstet Gynaecol Can. 2011; 33: 643-656
        • Wan J.J.
        • Schrimmer D.
        • Quinn K.
        • et al.
        Current practices in determining amnionicity and chorionicity in multiple gestations.
        Prenat Diagn. 2011; 31: 125-130
        • Hill L.M.
        • Chenevey P.
        • Hecker J.
        • Martin J.G.
        Sonographic determination of first trimester twin chorionicity and amnionicity.
        J Clin Ultrasound. 1996; 24: 305-308
        • Stenhouse E.
        • Hardwick C.
        • Maharaj S.
        • Webb J.
        • Kelly T.
        • Mackenzie F.M.
        Chorionicity determination in twin pregnancies: how accurate are we.
        Ultrasound Obstet Gynecol. 2002; 19: 350-352
        • Carroll S.G.
        • Soothill P.W.
        • Abdel-Fattah S.A.
        • Porter H.
        • Montague I.
        • Kyle P.M.
        Prediction of chorionicity in twin pregnancies at 10-14 weeks of gestation.
        BJOG. 2002; 109: 182-186
        • Dias T.
        • Arcangeli T.
        • Bhide A.
        • Napolitano R.
        • Mahsud-Dornan S.
        • Thilaganathan B.
        First-trimester ultrasound determination of chorionicity in twin pregnancy.
        Ultrasound Obstet Gynecol. 2011; 38: 530-532
        • Blumenfeld Y.J.
        • Momirova V.
        • Rouse D.J.
        • et al.
        Accuracy of sonographic chorionicity classification in twin gestations.
        J Ultrasound Med. 2014; 33: 2187-2192
        • Manzanares S.
        • Benítez A.
        • Naveiro-Fuentes M.
        • López-Criado M.S.
        • Sánchez-Gila M.
        Accuracy of fetal sex determination on ultrasound examination in the first trimester of pregnancy.
        J Clin Ultrasound. 2016; 44: 272-277
        • Hsiao C.H.
        • Wang H.C.
        • Hsieh C.F.
        • Hsu J.J.
        Fetal gender screening by ultrasound at 11 to 13(+6) weeks.
        Acta Obstet Gynecol Scand. 2008; 87: 8-13
        • Odeh M.
        • Granin V.
        • Kais M.
        • Ophir E.
        • Bornstein J.
        Sonographic fetal sex determination.
        Obstet Gynecol Surv. 2009; 64: 50-57
        • Perlman E.J.
        • Stetten G.
        • Tuck-Miller C.M.
        • et al.
        Sexual discordance in monozygotic twins.
        Am J Med Genet. 1990; 37: 551-557
        • Nieuwint A.
        • Zalen-Sprock R.
        • Van Hummel P.
        • et al.
        “Identical” twins with discordant karyotypes.
        Prenat Diagn. 1999; 19: 72-76
        • Machin G.
        Non-identical monozygotic twins, intermediate twin types, zygosity testing, and the non-random nature of monozygotic twinning: a review.
        Am J Med Genet C Semin Med Genet. 2009; 151C: 110-127
        • Silva S.
        • Martins Y.
        • Matias A.
        • Blickstein I.
        Why are monozygotic twins different?.
        J Perinat Med. 2011; 39: 195-202
        • Zech N.H.
        • Wisser J.
        • Natalucci G.
        • Riegel M.
        • Baumer A.
        • Schinzel A.
        Monochorionic-diamniotic twins discordant in gender from a naturally conceived pregnancy through postzygotic sex chromosome loss in a 47, XXY zygote.
        Prenat Diagn. 2008; 28: 759-763
        • Chitrit Y.
        • Vuillard E.
        • Khung S.
        • et al.
        Cloaca in discordant monoamniotic twins: prenatal diagnosis and consequence for fetal lung development.
        Am J Perinatol Rep. 2014; 4: 33-36
        • Souter V.L.
        • Kapur R.P.
        • Nyholt D.R.
        • et al.
        A report of dizygous monochorionic twins.
        N Engl J Med. 2003; 349: 154-158
        • Wachtel S.S.
        • Somkuti S.G.
        • Schinfeld J.S.
        Monozygotic twins of opposite sex.
        Cytogenet Cell Genet. 2000; 91: 293-295
        • Prior H.M.
        • Walter M.A.
        SOX genes: architects of development.
        Mol Med. 1996; 2: 405-412
        • Wolf U.
        Reorganization of the sex-determining pathway with the evolution of placentation.
        Hum Genet. 1999; 105: 288-292
        • Kondo S.
        • Schutte B.C.
        • Richardson R.J.
        • et al.
        Mutations in IRF6 cause Van der Woude and popliteal pterygium syndromes.
        Nat Genet. 2002; 32: 285-289
        • Peng H.H.
        • Kuo P.L.
        • Chao A.S.
        • et al.
        Discordant semilobar holoprosencephaly in monozygotic twins with de novo inv dup(15) marker chromosome and de novo mutation on SHH gene.
        Fetal Diagn Ther. 2007; 22: 389-393
        • Bick D.P.
        • McCorkle D.
        • Stanley W.S.
        • et al.
        Prenatal diagnosis of Smith–Lemli–Opitz syndrome in a pregnancy with low maternal serum estriol and a sex-reversed fetus.
        Prenat Diagn. 1999; 71: 68-71
        • Shinawi M.
        • Szabo S.
        • Popek E.
        • Wassif C.A.
        • Porter F.D.
        • Potocki L.
        Recognition of Smith-Lemli-Opitz syndrome (RSH) in the fetus: utility of ultrasonography and biochemical analysis in pregnancies with low maternal serum estriol.
        Am J Med Genet A. 2005; 138: 56-60
        • Nimkarn S.
        • New M.I.
        Prenatal diagnosis and treatment of congenital adrenal hyperplasia owing to 21-hydroxylase deficiency.
        Nat Clin Pr Endocrinol Metab. 2007; 3: 405-413
        • Yau M.
        • Khattab A.
        • New M.I.
        Prenatal diagnosis of congenital adrenal hyperplasia.
        Endocrinol Metab Clin North Am. 2016; 45: 267-281
        • De Paepe M.E.
        • Shapiro S.
        • Young L.
        • Luks F.I.
        Placental characteristics of selective birth weight discordance in diamniotic-monochorionic twin gestations.
        Placenta. 2010; 31: 380-386
        • Chen M.
        • Macias C.G.
        • Gunn S.K.
        • Dietrich J.E.
        • Roth D.R.
        • Schlomer B.J.
        Intrauterine growth restriction and hypospadias: is there a connection.
        Int J Pediatr Endocrinol. 2014; 2014: 20
        • Toufaily M.H.
        • Roberts D.J.
        • Westgate M.
        • Hunt A.
        • Holmes L.B.
        Hypospadias, intrauterine growth restriction, and abnormalities of the placenta.
        Birth Defects Res. 2017; 29: 1-6
        • Fredell L.
        • Lichtenstein P.
        • Pedersen N.L.
        • Svensson J.
        • Nordenskjöld A.
        Hypospadias is related to birth weight in discordant monozygotic twins.
        J Urol. 1998; 160: 2197-2199
        • Visser R.
        • Burger N.C.M.
        • Van Zwet E.W.
        • et al.
        Higher incidence of hypospadias in monochorionic twins.
        Twin Res Hum Genet. 2015; 18: 591-594
        • Williams C.A.
        • Wallace M.R.
        • Drury K.C.
        • et al.
        Blood lymphocyte chimerism associated with IVF and monochorionic dizygous twinning: case report.
        Hum Reprod. 2004; 19: 2816-2821
        • Kanda T.
        Confined blood chimerism in monochorionic dizygotic twins conceived spontaneously.
        AJP Rep. 2013; 3: 33-36
        • Smeets D.
        • van Vugt J.M.
        • Gomes I.
        • et al.
        Monochorionic dizygous twins presenting with blood chimerism and discordant sex.
        Twin Res Hum Genet. 2013; 16: 799-801
        • Lee H.J.
        • Yoon S.C.
        • Ko J.M.
        Monochorionic dizygotic twins with discordant sex and confined blood chimerism.
        Eur J Pediatr. 2014; 173: 1249-1252
        • Mayeur A.
        • Bras L.
        • Benachi A.
        • et al.
        Confined blood chimerism in a monochorionic dizygotic sex discordant twin pregnancy conceived after induced ovulation.
        Birth Defects Res A Clin Mol Teratol. 2016; 106: 298-303
        • Miura K.
        • Niikawa N.
        Do monochorionic dizygotic twins increase after pregnancy by assisted reproductive technology?.
        J Hum Genet. 2005; 50: 1-6
        • Peters H.E.
        • König T.E.
        • Verhoeven M.O.
        • et al.
        Unusual twinning resulting in chimerism: a systematic review on monochorionic dizygotic twins.
        Twin Res Hum Genet. 2017; 20: 161-168
        • Lopriore E.
        • Sueters M.
        • Middeldorp J.M.
        • Klumper F.
        • Oepkes D.
        • Vandenbussche F.P.
        Twin pregnancies with two separate placental masses can still be monochorionic and have vascular anastomoses.
        Am J Obstet Gynecol. 2006; 194: 804-808
        • Kim K.
        • Lage J.M.
        Bipartite diamnionic monochorionic twin placenta with superficial vascular anastomoses: report of a case.
        Hum Pathol. 1991; 22: 501-503
        • Altshuler G.
        • Hyde S.
        Placental pathology casebook: a bidiscoid, monochorionic placenta.
        J Perinatol. 1993; 13: 492-493
        • Walsh C.A.
        • Wilkinson M.
        • Downey P.
        • Mooney E.E.
        • Carroll S.
        “False” lambda sign in monochorionic twin pregnancy.
        Ultrasound Obstet Gynecol. 2015; 46: 376-377
        • Maruotti G.M.
        • Saccone G.
        • Morlando M.
        • Martinelli P.
        First-trimester ultrasound determination of chorionicity in twin gestations using the lambda sign: a systematic review and meta-analysis.
        Eur J Obstet Gynecol Reprod Biol. 2016; 202: 66-70
        • Sepulveda W.
        • Sebire N.J.
        • Hughes K.
        • Kalogeropoulos A.
        • Nicolaides K.H.
        Evolution of the lambda or twin-chorionic peak sign in dichorionic twin pregnancies.
        Obstet Gynecol. 1997; 89: 439-441
        • Gueneuc A.
        • Spaggiari E.
        • Bonniere M.
        • Hajal N.J.
        • Ville Y.
        • Salomon L.J.
        Pitfall in the diagnosis of chorionicity in twin pregnancy at first trimester.
        Ultrasound Obstet Gynecol. 2017; 49: 277-278
        • Chmait R.H.
        • Floyd R.
        • Benirschke K.
        Duplicity: sonography suggested a twin gestation was dichorionic-and monochorionic.
        Am J Obstet Gynecol. 2011; 205: 87.e1-87.e2
        • Yamashita A.
        • Ishii K.
        • Hidaka N.
        • et al.
        Monochorionic monozygotic twin pregnancy complicated with twin-twin transfusion syndrome presenting with an obvious lambda sign in the first trimester.
        Fetal Diagn Ther. 2015; 37: 154-156
        • Galjaard S.
        • Moerman P.
        • Corveleyn A.
        • Devlieger R.
        • Lewi L.
        Partial monochorionic and monoamniotic twin pregnancies: a report of two cases.
        Ultrasound Obstet Gynecol. 2014; 44: 722-724
        • Townsend R.R.
        • Simpson G.F.
        • Filly R.A.
        Membrane thickness in ultrasound prediction of chorionicity of twin gestations.
        J Ultrasound Med. 1988; 7: 327-332
        • Stagiannis K.D.
        • Sepulveda W.
        • Southwell D.
        • Price D.A.
        • Fisk N.M.
        Ultrasonographic measurement of the dividing membrane in twin pregnancy during the second and third trimesters: a reproducibility study.
        Am J Obstet Gynecol. 1995; 173: 1546-1550
        • Senat M.V.
        • Quarello E.
        • Levaillant J.M.
        • Buonumano A.
        • Boulvain M.
        • Frydman R.
        Determining chorionicity in twin gestations: three-dimensional (3D) multiplanar sonographic measurement of intra-amniotic membrane thickness.
        Ultrasound Obstet Gynecol. 2006; 28: 665-669
        • Bracero L.A.
        • Huff C.
        • Blitz M.J.
        • Plata M.J.
        • Seybold D.J.
        • Broce M.
        Ultrasound and histological measurements of dividing membrane thickness in twin gestations.
        Ultrasound Obstet Gynecol. 2016; 27: 470-475
        • Winn H.N.
        • Gabrielli S.
        • Reece E.A.
        • Roberts J.A.
        • Salafia C.
        • Hobbins J.C.
        Ultrasonographic criteria for the prenatal diagnosis of placental chorionicity in twin gestations.
        Am J Obstet Gynecol. 1989; 161: 1540-1542
        • Bracero L.A.
        • Byrne D.W.
        Ultrasound determination of chorionicity and perinatal outcome in twin pregnancies using dividing membrane thickness.
        Gynecol Obstet Invest. 2003; 55: 50-57
        • Leung T.Y.
        • Qu J.Z.
        • Liao G.J.
        • et al.
        Noninvasive twin zygosity assessment and aneuploidy detection by maternal plasma DNA sequencing.
        Prenat Diagn. 2013; 33: 675-681
        • Dias T.
        • Bhide A.
        • Papageorghiou A.T.
        • Thilaganathan B.
        Cord entanglement and perinatal outcome in monoamniotic twin pregnancies.
        Ultrasound Obstet Gynecol. 2010; 35: 201-204
        • Rossi A.C.
        • Prefumo F.
        Impact of cord entanglement on perinatal outcome of monoamniotic twins: a systematic review of the literature.
        Ultrasound Obstet Gynecol. 2013; 41: 131-135
        • Hack K.E.
        • van Gemert M.J.
        • Lopriore E.
        • et al.
        Placental characteristics of monoamniotic twin pregnancies in relation to perinatal outcome.
        Placenta. 2009; 30: 62-65
        • Patil A.S.
        • Martin J.
        • Tsukahara K.
        • et al.
        Pseudomonoamniotic pregnancy: case report and review of etiologic considerations.
        Fetal Pediatr Pathol. 2015; 34: 413-421
        • Hack K.E.
        • Nikkels P.G.
        • Koopman-Esseboom C.
        • et al.
        Placental characteristics of monochorionic diamniotic twin pregnancies in relation to perinatal outcome.
        Placenta. 2008; 29: 976-981
        • Bora S.A.
        • Papageorghiou A.T.
        • Bottomley C.
        • Kirk E.
        • Bourne T.
        Reliability of transvaginal ultrasonography at 7-9 weeks’ gestation in the determination of chorionicity and amnionicity in twin pregnancies.
        Ultrasound Obstet Gynecol. 2008; 32: 618-621
        • Ting Y.H.
        • Lao T.T.
        • Law K.M.
        • Cheng Y.K.
        • Lau T.K.
        • Leung T.Y.
        Pseudoamniotic band syndrome after in utero intervention for twin-to-twin transfusion syndrome: case reports and literature review.
        Fetal Diagn Ther. 2016; 40: 67-72
        • Lee K.J.
        • Kim M.K.
        • Lee S.Y.
        • Lee W.S.
        • Lee Y.H.
        Spontaneous rupture of the dividing membrane in a monochorionic pregnancy resulting in a pseudo-monoamniotic pregnancy with cord entanglement.
        J Obstet Gynecol. 2012; 38: 863-866
        • Fleming T.
        • Miller T.
        Spontaneous septostomy in mono- chorionic diamniotic twins resulting in cord entanglement and fetal demise.
        Australas J Ultrasound Med. 2012; 15: 103-106
        • Nasrallah F.K.
        • Faden Y.A.
        Antepartum rupture of the intertwin-dividing membrane in monochorionic diamniotic twins: a case report and review of the literature.
        Prenat Diagn. 2005; 25: 856-860
        • Jeanty C.
        • Newman E.
        • Jeanty P.
        • Rodts-Palenik S.
        Prenatal diagnosis of spontaneous septostomy in dichorionic diamniotic twins and review of the literature.
        J Ultrasound Med. 2010; 29: 455-463
        • Gilbert W.M.
        • Davis S.E.
        • Kaplan C.
        • Pretorius D.
        • Merritt T.A.
        • Benirschke K.
        Morbidity associated with prenatal disruption of the dividing membrane in twin gestations.
        Obstet Gynecol. 1991; 78: 623-630
        • Chmait R.H.
        • Aghajanian P.
        • Kontopoulos E.V.
        • Quintero R.A.
        Prenatal diagnosis of spontaneous septostomy of the dividing membranes in complicated monochorionic diamniotic multiple gestations.
        J Ultrasound Med. 2009; 28: 663-668
        • Chadha R.
        • Lange I.R.
        • Bratz L.
        • Cooper S.L.
        • Roggensack A.
        • Johnson J.
        A rare case of antepartum spontaneous septostomy in a monochorionic diamniotic twin pregnancy.
        Case Rep Obstet Gynecol. 2012; 2012: 748614
        • Bromley B.
        • Benacerraf B.
        Using the number of yolk sacs to determine amnionicity in early first trimester monochorionic twins.
        J Ultrasound Med. 1995; 14: 415-419
        • Beck F.
        • Moffat D.B.
        • Davies D.P.
        Human embryology.
        2nd ed. Blackwell Scientific Publications, London1985
        • Shen O.
        • Samueloff A.
        • Beller U.
        • Rabinowitz R.
        Number of yolk sacs does not predict amnionicity in early first-trimester monochorionic multiple gestations.
        Ultrasound Obstet Gynecol. 2006; 27: 53-55
        • Bishop D.K.
        Yolk-sac number in monoamniotic twins.
        Obstet Gynecol. 2010; 116: 504-507
        • Murakoshi T.
        • Ishii K.
        • Matsushita M.
        • Shinno T.
        • Naruse H.
        • Torii Y.
        Monochorionic monoamniotic twin pregnancies with two yolk sacs may not be a rare finding: a report of two cases.
        Ultrasound Obstet Gynecol. 2010; 36: 384-386
        • Corbett S.L.
        • Shmorgun D.
        Yolk sac number does not predict reliably amnionicity in monochorionic twin pregnancies: a case of a monochorionic monoamniotic twin pregnancy with two distinct yolk sacs on early first-trimester ultrasound.
        Ultrasound Obstet Gynecol. 2012; 39: 607-608

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