Double trouble? Clinic-specific risk factors for monozygotic twinning


      To investigate clinic-specific risk factors for monozygotic twinning (MZT) using a large, electronic database.


      Retrospective case-control study.


      Infertility clinics.


      Using an electronic medical record system, viable clinical pregnancy (confirmation of a gestational sac(s) and presence of at least one fetal pole with a heartbeat on first trimester ultrasound), data were obtained from homologous in vitro fertilization (IVF) cycles after single ET from June 1, 2004, to December 31, 2016. Monozygotic twinning was defined as a pregnancy with two fetal heartbeats on ultrasound with sex concordance at birth.



      Main Outcome Measure(s)

      Risk factors for MZT including cycle type, method of insemination, and method of cryopreservation.


      Of the 28,265 IVF cycles that met inclusion criteria over the study period, 8,749 (31.0%) resulted in a viable intrauterine clinical pregnancy. There were 102 (2.7%) MZT in the fresh cycle cohort and 133 (2.7%) in the frozen cycle cohort. Neither cryopreservation nor the method of cryopreservation was a significant risk factor for MZT. However, the use of sequential media was an independent risk factor for MZT in fresh, but not frozen, ETs (odds ratio = 1.72, 95% confidence interval, 1.10–2.68). Significant differences were seen in the incidence of MZT between clinics, and this difference persisted after controlling for known risk factors (clinic 0, reference; clinic 2, odds ratio = 2.22; 95% confidence interval, 1.48–3.32; clinic 3, odds ratio = 1.93; 95% confidence interval, 1.30–2.87).


      Differences in MZT rates exist between individual IVF clinics, suggesting that variations in practice patterns may contribute to this event. The present study noted the use of sequential media was an independent risk factor for fresh but not frozen cycles.
      Doble problema? Factores de riesgo clínicos específicos para embarazos gemelares monozigóticos.


      Investigar los factores de riesgo clínicos específicos para los embarazos gemelares monozigóticos (MZT) utilizando una gran base de datos electrónica.


      Estudio restrospectivo de casos y controles.


      Clínica de Infertilidad.


      Utilizando un sistema electrónico de recogida de datos médicos, se recogieron los datos de los ciclos con embarazos viables clínicamente (confirmación de un saco(s) gestacional y presencia de al menos un polo fetal con latido cardiaco en la ecografía de primer trimestre), de ciclos de FIV homólogos con una TE de un único embrión entre el 1 de junio de 2004 y 31 de diciembre de 2016. El embarazo gemelar monozigótico se definió como la presencia de 2 latidos cardiacos en la ecografía con concordancia de sexo al nacimiento.



      Medida(s) del resultado(s) principal(es)

      Factores de riesgo para MZT incluyendo tipo de ciclo, técnica de inseminación y técnica de criopreservación.


      De los 28,265 ciclos que cumplían los criterios de inclusión durante el periodo de estudio, 8,749 (31%) resultaron en un embarazo clínico intrauterino viable. Hubo 102 (2.7%) MZT en la cohorte de ciclos en fresco y 133 (2.7%) en la cohorte de ciclos de congelados.
      Ni la técnica de criopreservación ni la criopreservación en sí misma fueron factores de riesgo significativos para MZT. Sin embargo, el uso de medios secuenciales fue un factor de riesgo independiente para MZT en ciclos de ET en fresco, pero no en ciclos de embriones congelados (odds ratio =1.72, intervalo de confianza del 95% 1.10-2.68). Se observaron diferencias significativas en la incidencia de MZT entre clínicas y esta diferencia persistía después de controlar para factores de riesgo conocidos (clínica 0 referencia; clínica 2, odds ratio =2.22; intervalo de confianza 1.48-3.32; clínica 3, odds ratio =1.93; intervalo de confianza del 95% 1.30-2.87).


      Existen diferencias en las tasas de MZT entre clínicas, sugiriendo que las variaciones en los patrones de prácticas pueden contribuir a este hecho. El presente estudio halló que el uso de medio secuenciales era un factor independiente de riesgo en los ciclos en fresco, pero no en los ciclos de congelados.

      Key Words

      To read this article in full you will need to make a payment


      Subscribe to Fertility and Sterility
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Martin J.A.
        • Hamilton B.E.
        • Osterman M.J.
        Three decades of twin births in the United States, 1980-2009.
        NCHS Data Brief. 2012; : 1-8
        • Sunderam S.
        • Kissin D.M.
        • Crawford S.B.
        • Folger S.G.
        • Jamieson D.J.
        • Warner L.
        • et al.
        Assisted reproductive technology surveillance—United States, 2014.
        MMWR Surveill Summ. 2017; 66: 1-24
      1. Centers for Disease Control and Prevention. 2015 Assisted Reproductive Technology National Summary Report. In:59–60.

        • Sherer D.M.
        Adverse perinatal outcome of twin pregnancies according to chorionicity: review of the literature.
        Am J Perinatol. 2001; 18: 23-37
        • Hack K.E.
        • Derks J.B.
        • Elias S.G.
        • Franx A.
        • Roos E.J.
        • Voerman S.K.
        • et al.
        Increased perinatal mortality and morbidity in monochorionic versus dichorionic twin pregnancies: clinical implications of a large Dutch cohort study.
        Br J Obstet Gynaecol. 2008; 115: 58-67
        • MacDorman M.F.
        • Hoyert D.L.
        • Martin J.A.
        • Munson M.L.
        • Hamilton B.E.
        Fetal and perinatal mortality, United States, 2003.
        Natl Vital Stat Rep. 2007; 55: 1-17
        • Derom C.
        • Vlietinck R.
        • Derom R.
        • Van den Berghe H.
        • Thiery M.
        Increased monozygotic twinning rate after ovulation induction.
        Lancet. 1987; 1: 1236-1238
        • 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
        • Knopman J.M.
        • Krey L.C.
        • Oh C.
        • Lee J.
        • McCaffrey C.
        • Noyes N.
        What makes them split? Identifying risk factors that lead to monozygotic twins after in vitro fertilization.
        Fertil Steril. 2014; 102: 82-89
        • Vaughan D.A.
        • Ruthazer R.
        • Penzias A.S.
        • Norwitz E.R.
        • Sakkas D.
        Clustering of monozygotic twinning in IVF.
        J Assist Reprod Genet. 2016; 33: 19-26
        • Blickstein I.
        Estimation of iatrogenic monozygotic twinning rate following assisted reproduction: pitfalls and caveats.
        Am J Obstet Gynecol. 2005; 192: 365-368
        • 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
        • Bamforth F.
        • Machin G.
        Why zygosity of multiple births is not always obvious: an examination of zygosity testing requests from twins or their parents.
        Twin Res. 2004; 7: 406-411
        • van Jaarsveld C.H.
        • Llewellyn C.H.
        • Fildes A.
        • Fisher A.
        • Wardle J.
        Are my twins identical: parents may be misinformed by prenatal scan observations.
        Br J Obstet Gynaecol. 2012; 119: 517-518
        • Aston K.I.
        • Peterson C.M.
        • Carrell D.T.
        Monozygotic twinning associated with assisted reproductive technologies: a review.
        Reproduction. 2008; 136: 377-386
        • Ikemoto Y.
        • Kuroda K.
        • Ochiai A.
        • Yamashita S.
        • Ikuma S.
        • Nojiri S.
        • et al.
        Prevalence and risk factors of zygotic splitting after 937 848 single embryo transfer cycles.
        Hum Reprod. 2018; 33: 1984-1991
        • Skiadas C.C.
        • Missmer S.A.
        • Benson C.B.
        • Gee R.E.
        • Racowsky C.
        Risk factors associated with pregnancies containing a monochorionic pair following assisted reproductive technologies.
        Hum Reprod. 2008; 23: 1366-1371
        • Tarlatzis B.C.
        • Qublan H.S.
        • Sanopoulou T.
        • Zepiridis L.
        • Grimbizis G.
        • Bontis J.
        Increase in the monozygotic twinning rate after intracytoplasmic sperm injection and blastocyst stage embryo transfer.
        Fertil Steril. 2002; 77: 196-198
        • Frankfurter D.
        • Trimarchi J.
        • Hackett R.
        • Meng L.
        • Keefe D.
        Monozygotic pregnancies from transfers of zona-free blastocysts.
        Fertil Steril. 2004; 82: 483-485
        • Kawachiya S.
        • Bodri D.
        • Shimada N.
        • Kato K.
        • Takehara Y.
        • Kato O.
        Blastocyst culture is associated with an elevated incidence of monozygotic twinning after single embryo transfer.
        Fertil Steril. 2011; 95: 2140-2142
        • Menezo Y.J.
        • Sakkas D.
        Monozygotic twinning: is it related to apoptosis in the embryo?.
        Hum Reprod. 2002; 17: 247-248
        • Franasiak J.M.
        • Dondik Y.
        • Molinaro T.A.
        • Hong K.H.
        • Forman E.J.
        • Werner M.D.
        • et al.
        Blastocyst transfer is not associated with increased rates of monozygotic twins when controlling for embryo cohort quality.
        Fertil Steril. 2015; 103: 95-100
        • Sobek Jr., A.
        • Zborilova B.
        • Prochazka M.
        • Silhanova E.
        • Koutna O.
        • Klaskova E.
        • et al.
        High incidence of monozygotic twinning after assisted reproduction is related to genetic information, but not to assisted reproduction technology itself.
        Fertil Steril. 2015; 103: 756-760
        • Tagliani-Ribeiro A.
        • Paskulin D.D.
        • Oliveira M.
        • Zagonel-Oliveira M.
        • Longo D.
        • Ramallo V.
        • et al.
        High twinning rate in Candido Godoi: a new role for p53 in human fertility.
        Hum Reprod. 2012; 27: 2866-2871
        • Meintjes M.
        Culture media, solutions, and systems in human ART.
        in: Quinn P. Monozygotic twinning and assisted reproduction laboratory or clinical? Cambridge University Press, Cambridge2014: 189-223
        • Vega M.
        • Zaghi S.
        • Buyuk E.
        • Jindal S.
        Not all twins are monozygotic after elective single embryo transfer: analysis of 32,600 elective single embryo transfer cycles as reported to the Society for Assisted Reproductive Technology.
        Fertil Steril. 2018; 109: 118-122
        • Edwards R.G.
        • Mettler L.
        • Walters D.E.
        Identical twins and in vitro fertilization.
        J In Vitro Fert Embryo Transf. 1986; 3: 114-117
        • Wells D.
        • Bermudez M.G.
        • Steuerwald N.
        • Malter H.E.
        • Thornhill A.R.
        • Cohen J.
        Association of abnormal morphology and altered gene expression in human preimplantation embryos.
        Fertil Steril. 2005; 84: 343-355
        • Mateizel I.
        • Santos-Ribeiro S.
        • Done E.
        • Van Landuyt L.
        • Van de Velde H.
        • Tournaye H.
        • et al.
        Do ARTs affect the incidence of monozygotic twinning?.
        Hum Reprod. 2016; 31: 2435-2441
        • Papanikolaou E.G.
        • Fatemi H.
        • Venetis C.
        • Donoso P.
        • Kolibianakis E.
        • Tournaye H.
        • et al.
        Monozygotic twinning is not increased after single blastocyst transfer compared with single cleavage-stage embryo transfer.
        Fertil Steril. 2010; 93: 592-597
        • Otsuki J.
        • Iwasaki T.
        • Katada Y.
        • Sato H.
        • Furuhashi K.
        • Tsuji Y.
        • et al.
        Grade and looseness of the inner cell mass may lead to the development of monochorionic diamniotic twins.
        Fertil Steril. 2016; 106: 640-644
        • Goto S.
        • Kadowaki T.
        • Tanaka S.
        • Hashimoto H.
        • Kokeguchi S.
        • Shiotani M.
        Prediction of pregnancy rate by blastocyst morphological score and age, based on 1,488 single frozen-thawed blastocyst transfer cycles.
        Fertil Steril. 2011; 95: 948-952
        • Knopman J.
        • Krey L.C.
        • Lee J.
        • Fino M.E.
        • Novetsky A.P.
        • Noyes N.
        Monozygotic twinning: an eight-year experience at a large IVF center.
        Fertil Steril. 2010; 94: 502-510
        • Schachter M.
        • Raziel A.
        • Friedler S.
        • Strassburger D.
        • Bern O.
        • Ron-El R.
        Monozygotic twinning after assisted reproductive techniques: a phenomenon independent of micromanipulation.
        Hum Reprod. 2001; 16: 1264-1269
        • Alikani M.
        • Noyes N.
        • Cohen J.
        • Rosenwaks Z.
        Monozygotic twinning in the human is associated with the zona pellucida architecture.
        Hum Reprod. 1994; 9: 1318-1321
        • Behr B.
        • Fisch J.D.
        • Racowsky C.
        • Miller K.
        • Pool T.B.
        • Milki A.A.
        Blastocyst-ET and monozygotic twinning.
        J Assist Reprod Genet. 2000; 17: 349-351
        • Chang H.J.
        • Lee J.R.
        • Jee B.C.
        • Suh C.S.
        • Kim S.H.
        Impact of blastocyst transfer on offspring sex ratio and the monozygotic twinning rate: a systematic review and meta-analysis.
        Fertil Steril. 2009; 91: 2381-2390
        • Kanter J.R.
        • Boulet S.L.
        • Kawwass J.F.
        • Jamieson D.J.
        • Kissin D.M.
        Trends and correlates of monozygotic twinning after single embryo transfer.
        Obstet Gynecol. 2015; 125: 111-117
        • Sills E.S.
        • Moomjy M.
        • Zaninovic N.
        • Veeck L.L.
        • McGee M.
        • Palermo G.D.
        • et al.
        Human zona pellucida micromanipulation and monozygotic twinning frequency after IVF.
        Hum Reprod. 2000; 15: 890-895
        • Talansky B.E.
        • Gordon J.W.
        Cleavage characteristics of mouse embryos inseminated and cultured after zona pellucida drilling.
        Gamete Res. 1988; 21: 277-287
        • Luke B.
        • Brown M.B.
        • Wantman E.
        • Stern J.E.
        Factors associated with monozygosity in assisted reproductive technology pregnancies and the risk of recurrence using linked cycles.
        Fertil Steril. 2014; 101: 683-689
        • Haimov-Kochman R.
        • Daum H.
        • Lossos F.
        • Aizenman E.
        • Werner M.
        • Yagel S.
        • et al.
        Monozygotic multiple gestation after intracytoplasmic sperm injection and preimplantation genetic diagnosis.
        Fertil Steril. 2009; 92: 2037.e11-2037.e17
        • Verpoest W.
        • Van Landuyt L.
        • Desmyttere S.
        • Cremers A.
        • Devroey P.
        • Liebaers I.
        The incidence of monozygotic twinning following PGD is not increased.
        Hum Reprod. 2009; 24: 2945-2950
        • Tagliani-Ribeiro A.
        • Oliveira M.
        • Sassi A.K.
        • Rodrigues M.R.
        • Zagonel-Oliveira M.
        • Steinman G.
        • et al.
        Twin town in south Brazil: a Nazi's experiment or a genetic founder effect?.
        PLoS One. 2011; 6e20328
        • Maas K.
        • Galkina E.
        • Thornton K.
        • Penzias A.S.
        • Sakkas D.
        No change in live birthweight of IVF singleton deliveries over an 18-year period despite significant clinical and laboratory changes.
        Hum Reprod. 2016; 31: 1987-1996
        • Guilherme R.
        • Drunat S.
        • Delezoide A.L.
        • Oury J.F.
        • Luton D.
        Zygosity and chorionicity in triplet pregnancies: new data.
        Hum Reprod. 2009; 24: 100-105