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Twin Pregnancies, Crown-rump Length and Birthweight Discordancy: The Influence of Chorionicity

Gestações gemelares, comprimento craniocaudal e discordância de peso ao nascimento: a influência da corionicidade

Abstract

Objective

The purpose of the present study was to analyze the influence of chorionicity in the biometric parameters crown-rump length (CRL), birthweight (BW), crown-rump length discordancy (CRLD) and birthweight discordancy (BWD), determine the correlation between these latter two in cases of intertwin discordancy, and to analyze the influence of chronicity in the presence of these discordancies with clinical relevance (> 10% and > 15%, respectively).

Methods

The present study was a retrospective study based on the twin pregnancy database of the Centro Hospitalar S. João (2010-2015), including 486 fetuses among 66 monochorionic (MC) and 177 dichorionic gestations (DC). The inclusion criteria were multiple pregnancies with 2 fetuses and healthy twin gestations. The exclusion criteria were trichorionic gestations and pregnancies with inconclusive chorionicity, multiple pregnancy with ≥ 3 fetuses and pathological twin gestations.

Results

No statistically significant difference was found in BW (p = 0.09) and in its discordancy (p = 0.06) nor in CRL (p = 0.48) and its discordancy (p = 0.74) between MCs and DCs. Crown-rump length discordancy and birthweight discordancy were correlated by the regression line “BWD = 0.8864 x CRLD + 0.0743,” with r2 = 0.1599. Crown-rump length discordancy > 10% was found in 7.58% of monochorionic and in 13.56% of dichorionic twins. Birthweight discordancy > 15% was detected in 16.67% of monochorionic and in 31.64% of dichorionic twins.

Conclusion

No statistically significant influence of chorionicity was identified in both birthweight and birthweight discordancy, as in crown-rump length and crown-rump length discordancy. Birthweight discordancy was correlated to crown-rump length discordancy in 20% of cases.

Keywords:
fetal growth; growth discordancy; crown-rump length; birthweight; chorionicity; twins

Resumo

Objetivo

O objetivo do presente estudo foi analisar a influência da corionicidade nos parâmetros biométricos comprimento craniocaudal, peso ao nascimento, discordância de comprimento craniocaudal e discordância de peso ao nascimento, determinar a correlação entre estes dois últimos caso haja discordância intergemelar e analisar a influência da corionicidade na presença destas discordâncias com relevância clínica (> 10% e > 15%, respectivamente).

Métodos

O presente estudo foi um estudo retrospectivo baseado na base de dados de gestações gemelares do Centro Hospitalar S. João (2010-2015), incluindo 486 fetos de 66 gestações monocoriônicas e 177 dicoriônicas. Os critérios de inclusão foram gestações múltiplas de 2 fetos e gestações gemelares saudáveis. Os critérios de exclusão foram gestações tricoriônicas ou de corionicidade inconclusiva, gestações múltiplas com ≥ 3 fetos e gestações gemelares patológicas.

Resultados

Não se encontrou diferença estatisticamente significativa no peso ao nascimento (p =0,09) e sua discordância (p = 0,06) nem no comprimento craniocaudal (p = 0,48) e sua discordância (p = 0,74) entre gestações monocoriônicas e dicoriônicas. Considerando todas as gestações, as discordâncias de comprimento craniocaudal e peso ao nascimento foram correlacionadas pela reta de regressão “discordância de peso ao nascimento = 0.8864 x discordância de comprimento craniocaudal + 0.0743,” com r2 = 0,1599. A discordância de comprimento craniocaudal > 10% descobriu-se em 7.58% das gestações monocoriônicas e em 13.56% das dicoriônicas. A discordância de peso ao nascimento > 15% detectou-se em 16.67% das gestações monocoriônicas e em 31.64% das dicoriônicas.

Conclusão

Não se identificou influência estatisticamente significativa no peso ao nascimento e sua discordância, bem como no comprimento craniocaudal e sua discordância. A discordância de peso ao nascimento correlacionou-se com a discordância de comprimento craniocaudal em 20% dos casos.

Palavras-chave:
crescimento fetal; discordância de crescimento; comprimento craniocaudal; peso ao nascimento; corionicidade; gêmeos

Introduction

Twinning is increasing worldwide with increased maternal age and more common use of assisted reproduction. The higher risk of mortality and morbidity in multiples is widely recognized.11 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(01):66-69. Doi: 10.1111/1754-9485.12268
https://doi.org/10.1111/1754-9485.12268...
22 Mihailidis S, Bockmann M, McConnell E, et al. The influence of chorion type on health measures at birth and dental development in Australian and Dutch twins: a comparative study. Twin Res Hum Genet. 2015;18(04):368-374. Doi: 10.1017/thg.2015.43
https://doi.org/10.1017/thg.2015.43...
33 Kyono K. The precise timing of embryo splitting for monozygotic dichorionic diamniotic twins: when does embryo splitting for monozygotic dichorionic diamniotic twins occur? Evidence for splitting at the morula/blastocyst stage from studies of in vitro fertilization. Twin Res Hum Genet. 2013;16(04):827-832. Doi: 10.1017/thg.2013.32
https://doi.org/10.1017/thg.2013.32...
55 Oldenburg A, Rode L, Bødker B, Holmskov A, Jørgensen FS, Larsen H, et al. Influence of chorionicity on perinatal outcome in a large cohort of Danish twin pregnancies. Ultrasound Obstet Gynecol. 2012;39(01):69-74. Doi: 10.1002/uog.10057
https://doi.org/10.1002/uog.10057...
66 Glinianaia SV, Obeysekera MA, Sturgiss S, Bell R. Stillbirth and neonatal mortality in monochorionic and dichorionic twins: a population-based study. Hum Reprod. 2011;26(09):2549-2557. Doi: 10.1093/humrep/der213
https://doi.org/10.1093/humrep/der213...
77 Lee KA, Oh KJ, Lee SM, Kim A, Jun JK. The frequency and clinical significance of twin gestations according to zygosity and chorionicity. Twin Res Hum Genet. 2010;13(06):609-619. Doi: 10.1375/ twin.13.6.609
https://doi.org/10.1375/...
1010 Carroll SG, Tyfield L, Reeve L, Porter H, Soothill P, Kyle PM. Is zygosity or chorionicity the main determinant of fetal outcome in twin pregnancies? Am J Obstet Gynecol. 2005;193(3 Pt 1):757-761. Doi: 10.1016/j.ajog.2005.01.024
https://doi.org/10.1016/j.ajog.2005.01.0...
1111 Papageorghiou AT, Bakoulas V, Sebire NJ, Nicolaides KH. Intrauterine growth in multiple pregnancies in relation to fetal number, chorionicity and gestational age. Ultrasound Obstet Gynecol. 2008;32(07):890-893. Doi: 10.1002/uog.6140
https://doi.org/10.1002/uog.6140...
1212 Cleary-Goldman J, D'Alton ME. Growth abnormalities and multiple gestations. Semin Perinatol. 2008;32(03):206-212. Doi: 10.1053/j.semperi.2008.02.009
https://doi.org/10.1053/j.semperi.2008.0...
1616 Loos RJ, Derom C, Derom R, Vlietinck R. Determinants of birthweight and intrauterine growth in liveborn twins. Paediatr Perinat Epidemiol. 2005;19(Suppl 1):15-22. Doi: 10.1111/j.1365- 3016.2005.00611.x
https://doi.org/10.1111/j.1365-...
1717 González-Quintero VH, Luke B, O'sullivan MJ, Misiunas R, Anderson E, Nugent C, et al. Antenatal factors associated with significant birth weight discordancy in twin gestations. Am J Obstet Gynecol. 2003;189(03):813-817. Doi: 10.1067/s0002-9378(03) 00658-6
https://doi.org/10.1067/s0002-9378(03)...
1818 Senoo M, Okamura K, Murotsuki J, Yaegashi N, Uehara S, Yajima A. Growth pattern of twins of different chorionicity evaluated by sonographic biometry. Obstet Gynecol. 2000;95(05):656-661. Doi: 10.1016/s0029-7844(99)00645-6
https://doi.org/10.1016/s0029-7844(99)00...
1919 Araujo Júnior E, Ruano R, Javadian P, MartinsWP, Elito J Jr, Pires CR, Zanforlin Filho SM. Reference charts for fetal biometric parameters in twin pregnancies according to chorionicity. Prenat Diagn. 2014;34(04):382-388. Doi: 10.1002/pd.4318
https://doi.org/10.1002/pd.4318...
2424 Reberdao MA, Martins L, Torgal M, Viana R, Seminova T, Casal E, et al. The source of error in the estimation of intertwin birth weight discordance. J Perinat Med. 2010;38(06):671-674. Doi: 10.1515/JPM.2010.104
https://doi.org/10.1515/JPM.2010.104...
2626 Blickstein I, Goldman RD, Mazkereth R. Adaptive growth restriction as a pattern of birth weight discordance in twin gestations. Obstet Gynecol. 2000;96(06):986-990. Doi: 10.1016/s0029-7844 (00)01079-6
https://doi.org/10.1016/s0029-7844...
3030 Blickstein I, Kalish RB. Birthweight discordance in multiple pregnancy. Twin Res. 2003;6(06):526-531. Doi: 10.1375/13690520332 2686536
https://doi.org/10.1375/13690520332...
3232 Grande M, Goncé A, Stergiotou I, Bennasar M, Borrell A. Intertwin crown-rump length discordance in the prediction of fetal anomalies, fetal loss and adverse perinatal outcome. J Matern Fetal Neonatal Med. 2016;29(17):2883-2888. Doi: 10.3109/14767058. 2015.1107901
https://doi.org/10.3109/14767058...
3434 D'Antonio F, Khalil A, Pagani G, Papageorghiou AT, Bhide A, Thilaganathan B. Crown-rump length discordance and adverse perinatal outcome in twin pregnancies: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2014;44(02):138-146. Doi: 10.1002/uog.13335
https://doi.org/10.1002/uog.13335...
3535 Oepkes D, Sueters M. Antenatal fetal surveillance in multiple pregnancies. Best Pract Res Clin Obstet Gynaecol. 2017;38:59-70. Doi: 10.1016/j.bpobgyn.2016.09.004
https://doi.org/10.1016/j.bpobgyn.2016.0...
According to the classification of twin pregnancies, no matter how many fetuses we are dealing with (zygosity), what really counts for defining perinatal outcome of twin pregnancies is the type of placentation (chorionicity).11 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(01):66-69. Doi: 10.1111/1754-9485.12268
https://doi.org/10.1111/1754-9485.12268...
22 Mihailidis S, Bockmann M, McConnell E, et al. The influence of chorion type on health measures at birth and dental development in Australian and Dutch twins: a comparative study. Twin Res Hum Genet. 2015;18(04):368-374. Doi: 10.1017/thg.2015.43
https://doi.org/10.1017/thg.2015.43...
44 Farah N, Hogan J, Johnson S, Stuart B, Daly S. Prospective risk of fetal death in uncomplicated monochorionic twins. Acta Obstet Gynecol Scand. 2012;91(03):382-385. Doi: 10.1111/j.1600- 0412.2011.01288.x
https://doi.org/10.1111/j.1600-...
55 Oldenburg A, Rode L, Bødker B, Holmskov A, Jørgensen FS, Larsen H, et al. Influence of chorionicity on perinatal outcome in a large cohort of Danish twin pregnancies. Ultrasound Obstet Gynecol. 2012;39(01):69-74. Doi: 10.1002/uog.10057
https://doi.org/10.1002/uog.10057...
66 Glinianaia SV, Obeysekera MA, Sturgiss S, Bell R. Stillbirth and neonatal mortality in monochorionic and dichorionic twins: a population-based study. Hum Reprod. 2011;26(09):2549-2557. Doi: 10.1093/humrep/der213
https://doi.org/10.1093/humrep/der213...
1010 Carroll SG, Tyfield L, Reeve L, Porter H, Soothill P, Kyle PM. Is zygosity or chorionicity the main determinant of fetal outcome in twin pregnancies? Am J Obstet Gynecol. 2005;193(3 Pt 1):757-761. Doi: 10.1016/j.ajog.2005.01.024
https://doi.org/10.1016/j.ajog.2005.01.0...
2323 Blickstein I, Mincha S, Goldman RD, Machin GA, Keith LG. The Northwestern twin chorionicity study: testing the 'placental crowding' hypothesis. J Perinat Med. 2006;34(02):158-161. Doi: 10.1515/JPM.2006.028
https://doi.org/10.1515/JPM.2006.028...
3535 Oepkes D, Sueters M. Antenatal fetal surveillance in multiple pregnancies. Best Pract Res Clin Obstet Gynaecol. 2017;38:59-70. Doi: 10.1016/j.bpobgyn.2016.09.004
https://doi.org/10.1016/j.bpobgyn.2016.0...
However, in the literature, other authors favor a contrasting opinion.77 Lee KA, Oh KJ, Lee SM, Kim A, Jun JK. The frequency and clinical significance of twin gestations according to zygosity and chorionicity. Twin Res Hum Genet. 2010;13(06):609-619. Doi: 10.1375/ twin.13.6.609
https://doi.org/10.1375/...
Furthermore, the importance of chorionicity on twin growth patterns is well-established, being monochorionic twin gestations (MC) the ones with a less favorable scenario. In fact, growth restriction, low birthweight (BW) and birthweight discordancy > 25% are common findings in multiple pregnancies, mainly among MC twins.88 Ortibus E, Lopriore E, Deprest J, Vandenbussche FP, Walther FJ, Diemert A, et al. The pregnancy and long-term neurodevelopmental outcome of monochorionic diamniotic twin gestations: a multicenter prospective cohort study from the first trimester onward. Am J Obstet Gynecol. 2009;200(05):494.e1-494.e8. Doi: 10.1016/j.ajog.2009.01.048
https://doi.org/10.1016/j.ajog.2009.01.0...
2121 Lewi L, Cannie M, Blickstein I, Jani J, Huber A, Huecher K, et al. Placental sharing, birthweight discordance, and vascular anastomoses in monochorionic diamniotic twin placentas. Am J Obstet Gynecol. 2007;197(06):587.e1-587.e8. Doi: 10.1016/j. ajog.2007.05.009
https://doi.org/10.1016/j...
2323 Blickstein I, Mincha S, Goldman RD, Machin GA, Keith LG. The Northwestern twin chorionicity study: testing the 'placental crowding' hypothesis. J Perinat Med. 2006;34(02):158-161. Doi: 10.1515/JPM.2006.028
https://doi.org/10.1515/JPM.2006.028...
2424 Reberdao MA, Martins L, Torgal M, Viana R, Seminova T, Casal E, et al. The source of error in the estimation of intertwin birth weight discordance. J Perinat Med. 2010;38(06):671-674. Doi: 10.1515/JPM.2010.104
https://doi.org/10.1515/JPM.2010.104...
2727 Hack KE, van Gemert MJ, Lopriore E, Schaap AHP, Eggink AJ, Elias SG, et al. Placental characteristics of monoamniotic twin pregnancies in relation to perinatal outcome. Placenta. 2009;30(01): 62-65. Doi: 10.1016/j.placenta.2008.09.016
https://doi.org/10.1016/j.placenta.2008....
2828 Lopriore E, Pasman SA, Klumper FJ, Middeldorp JM, Walther FJ, Oepkes D. Placental characteristics in growth-discordant monochorionic twins: a matched case-control study. Placenta. 2012;33 (03):171-174. Doi: 10.1016/j.placenta.2011.12.004
https://doi.org/10.1016/j.placenta.2011....
2929 Simões T, Cordeiro A, Júlio C, Reis J, Dias E, Blickstein I. Perinatal outcome and change in body mass index inmothers of dichorionic twins: a longitudinal cohort study. Twin Res Hum Genet. 2008;11 (02):219-223. Doi: 10.1375/twin.11.2.219
https://doi.org/10.1375/twin.11.2.219...
3030 Blickstein I, Kalish RB. Birthweight discordance in multiple pregnancy. Twin Res. 2003;6(06):526-531. Doi: 10.1375/13690520332 2686536
https://doi.org/10.1375/13690520332...
3131 Lopriore E, Sluimers C, Pasman SA, Middeldorp JM, Oepkes D, Walther FJ. Neonatal morbidity in growth-discordant monochorionic twins: comparison between the larger and the smaller twin. Twin Res Hum Genet. 2012;15(04):541-546. Doi: 10.1017/ thg.2012.26
https://doi.org/10.1017/...
3535 Oepkes D, Sueters M. Antenatal fetal surveillance in multiple pregnancies. Best Pract Res Clin Obstet Gynaecol. 2017;38:59-70. Doi: 10.1016/j.bpobgyn.2016.09.004
https://doi.org/10.1016/j.bpobgyn.2016.0...
3636 Jahanfar S, Lim K, Oviedo-Joekes E. Optimal threshold for birth weight discordance: Does knowledge of chorionicity matter? J Perinatol. 2016;36(09):704-712. Doi: 10.1038/jp.2016.82
https://doi.org/10.1038/jp.2016.82...
Birthweight discordancy affects up to 20% of MC and only 8% of dichorionic twin gestations (DC), being unequal placental sharing the major contributor.2121 Lewi L, Cannie M, Blickstein I, Jani J, Huber A, Huecher K, et al. Placental sharing, birthweight discordance, and vascular anastomoses in monochorionic diamniotic twin placentas. Am J Obstet Gynecol. 2007;197(06):587.e1-587.e8. Doi: 10.1016/j. ajog.2007.05.009
https://doi.org/10.1016/j...
2828 Lopriore E, Pasman SA, Klumper FJ, Middeldorp JM, Walther FJ, Oepkes D. Placental characteristics in growth-discordant monochorionic twins: a matched case-control study. Placenta. 2012;33 (03):171-174. Doi: 10.1016/j.placenta.2011.12.004
https://doi.org/10.1016/j.placenta.2011....
This condition can be divided into 3 categories: < 15% (concordant growth), 15–25% (mildly discordant growth) and > 25% (severely discordant growth).2020 Blickstein I, Keith LG. Neonatal mortality rates among growthdiscordant twins, classified according to the birth weight of the smaller twin. Am J Obstet Gynecol. 2004;190(01):170-174. Doi: 10.1016/j.ajog.2003.07.025
https://doi.org/10.1016/j.ajog.2003.07.0...
2222 Simoes T, Julio C, Cordeiro A, Cohen A, Silva A, Blickstein I. Abdominal circumference ratio for the diagnosis of intertwin birth weight discordance. J Perinat Med. 2011;39(01):43-46. Doi: 10.1515/JPM.2010.124
https://doi.org/10.1515/JPM.2010.124...
2424 Reberdao MA, Martins L, Torgal M, Viana R, Seminova T, Casal E, et al. The source of error in the estimation of intertwin birth weight discordance. J Perinat Med. 2010;38(06):671-674. Doi: 10.1515/JPM.2010.104
https://doi.org/10.1515/JPM.2010.104...
2525 Blickstein I, Shoham-Schwartz Z, Lancet M, Borenstein R. Characterization of the growth-discordant twin. Obstet Gynecol. 1987; 70(01):11-152626 Blickstein I, Goldman RD, Mazkereth R. Adaptive growth restriction as a pattern of birth weight discordance in twin gestations. Obstet Gynecol. 2000;96(06):986-990. Doi: 10.1016/s0029-7844 (00)01079-6
https://doi.org/10.1016/s0029-7844...
3030 Blickstein I, Kalish RB. Birthweight discordance in multiple pregnancy. Twin Res. 2003;6(06):526-531. Doi: 10.1375/13690520332 2686536
https://doi.org/10.1375/13690520332...
3636 Jahanfar S, Lim K, Oviedo-Joekes E. Optimal threshold for birth weight discordance: Does knowledge of chorionicity matter? J Perinatol. 2016;36(09):704-712. Doi: 10.1038/jp.2016.82
https://doi.org/10.1038/jp.2016.82...
These abnormal growth patterns related to chorionicity cause worse outcomes since the obstetric management is not well-established yet.2828 Lopriore E, Pasman SA, Klumper FJ, Middeldorp JM, Walther FJ, Oepkes D. Placental characteristics in growth-discordant monochorionic twins: a matched case-control study. Placenta. 2012;33 (03):171-174. Doi: 10.1016/j.placenta.2011.12.004
https://doi.org/10.1016/j.placenta.2011....
3131 Lopriore E, Sluimers C, Pasman SA, Middeldorp JM, Oepkes D, Walther FJ. Neonatal morbidity in growth-discordant monochorionic twins: comparison between the larger and the smaller twin. Twin Res Hum Genet. 2012;15(04):541-546. Doi: 10.1017/ thg.2012.26
https://doi.org/10.1017/...
The use of first trimester transvaginal ultrasonography is therefore mandatory to obtain an early accurate determination of multiple gestations, to define their chorionicity and zygosity, as well as to calculate some important biometric parameters such as crown-rump length (CRL) and its inter-twin discordancy.11 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(01):66-69. Doi: 10.1111/1754-9485.12268
https://doi.org/10.1111/1754-9485.12268...
99 Sherer DM. Is less intensive fetal surveillance of dichorionic twin gestations justified? Ultrasound Obstet Gynecol. 2000;15(03): 167-173. Doi: 10.1046/j.1469-0705.2000.00072.x
https://doi.org/10.1046/j.1469-0705.2000...
3535 Oepkes D, Sueters M. Antenatal fetal surveillance in multiple pregnancies. Best Pract Res Clin Obstet Gynaecol. 2017;38:59-70. Doi: 10.1016/j.bpobgyn.2016.09.004
https://doi.org/10.1016/j.bpobgyn.2016.0...
Some authors have analyzed this inter-twin CRL discordancy (CRLD), which is considered to be of major clinical importance when ≥ 10%, as a predictor of an increased risk for fetal anomalies and growth restriction, affecting BW in the long run.3232 Grande M, Goncé A, Stergiotou I, Bennasar M, Borrell A. Intertwin crown-rump length discordance in the prediction of fetal anomalies, fetal loss and adverse perinatal outcome. J Matern Fetal Neonatal Med. 2016;29(17):2883-2888. Doi: 10.3109/14767058. 2015.1107901
https://doi.org/10.3109/14767058...
3333 Ben-Ami I, Sheena L, Svirsky R, Odeh M, Rosen H, Melcer Y, Maymon R. The association of crown-rump length discrepancy with birthweight discordance in spontaneous versus assisted conception dichorionic twins. Prenat Diagn. 2014;34(08): 748-752. Doi: 10.1002/pd.4359
https://doi.org/10.1002/pd.4359...
Contrarily, other studies classified the CRLD as a poor predictor of adverse outcome due to its lack of accuracy, proving useless as a screening method in the current clinical practice.3333 Ben-Ami I, Sheena L, Svirsky R, Odeh M, Rosen H, Melcer Y, Maymon R. The association of crown-rump length discrepancy with birthweight discordance in spontaneous versus assisted conception dichorionic twins. Prenat Diagn. 2014;34(08): 748-752. Doi: 10.1002/pd.4359
https://doi.org/10.1002/pd.4359...
3434 D'Antonio F, Khalil A, Pagani G, Papageorghiou AT, Bhide A, Thilaganathan B. Crown-rump length discordance and adverse perinatal outcome in twin pregnancies: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2014;44(02):138-146. Doi: 10.1002/uog.13335
https://doi.org/10.1002/uog.13335...
The purpose of the present study was to analyze the influence of chorionicity in the biometric parameters CRL, BW, CRLD and BWD, determine the correlation between these latter two in cases of inter-twin discordancy, and to analyze the influence of chronicity in the presence of these discordancies with clinical relevance (> 10% and > 15%, respectively).

Methods

The present study was a retrospective study based on the twin pregnancy database of Centro Hospitalar S. João related to a period of 5 years (2010–2015). We considered a total of 706 fetuses. From those, we included 486 fetuses, 132 from 66 MC (each one with fetus 1 and fetus 2) and 354 from 177 DC (each one with fetus 1 and fetus 2). The inclusion criteria were multiple pregnancies with 2 fetuses and healthy twin gestations. The exclusion criteria were trichorionic gestations and pregnancies with inconclusive chorionicity, multiple pregnancies with ≥ 3 fetuses and pathological twin gestations. By healthy and nonpathological twin gestations, the authors considered gestations without malformed fetuses or other fetal pathologies that could interfere in the spontaneous inter-twin discordancy, congenital anomalies, twin-to-twin transfusion syndrome, selective intrauterine growth restriction and presence of maternal pathologies (pre-eclampsia, diabetes, etc). In this database, we considered two biometric parameters: CRL, evaluated in the 1st trimester obstetric ultrasound (performed between the 11th and 14th weeks of gestation), as well as BW, confirmed after birth. Chorionicity was confirmed in the 1st trimester obstetric ultrasound. The defined objectives for the statistical analysis were: 1st – analyze individually the biometric parameters CRL, BW, CRLD and birthweight discordancy, according to chorionicity (among 3 different samples – all fetuses, only fetuses 1 and only fetuses 2–concerning CRL and BW, and among all gestations, concerning CRLD and birthweight discordancy); 2nd- determine the association between CRLD and birthweight discordancy and analyze the regression line of their association graph; 3rd – discordancy of CRL and discordancy of BW were analyzed for both MCs and DCs considering as clinically relevant a CRLD > 10% and a birthweight discordancy > 15%. The discordancy of each parameter was calculated by using the ratio between the difference of the measurements of the two fetuses of the same gestation and the larger measurement between them. The first objective was used to demonstrate that the population of MCs and DCs is comparable since the study included only twin pregnancies that had a normal outcome. In this case, it is possible to evaluate the early ultrasound parameters and their birthweight discordancy in the two populations studied. The statistical analysis was performed using IBM SPSS Statistics for Windows, Version 23 (IBM Corp., Armonk, NY, USA), and the chosen significance value for the applied statistical tests was 0.05. The present investigation was approved by the ethics committee of the hospital and authorized by the Centro Hospitalar S. João Board of Directors.

Results

For the 1st objective, we analyzed the data from 3 different samples (all fetuses, fetuses 1 and fetuses 2) concerning CRL and BW according to their chorionicity. Regarding the influence of chorionicity type among all fetuses, we obtained, with the parametric t-test, p = 0.48 (> 0.05), for CRL, and p = 0.09 (> 0.05), for BW. Concerning the influence of chorionicity for fetuses 1, we obtained, with the parametric t-test, p = 0.68 (> 0.05), for the CRL, and p = 0.12 (> 0.05), for BW. In what concerns the influence of chorionicity for fetuses 2, we obtained, with the parametric t-test, p = 0.56 (> 0.05), for CRL, and p = 0.40 (> 0.05), for BW. All these results are depicted in Table 1.

Table 1
Influence of chorionicity in crown-rump length (mm) and birthweight (g)

Second, we also analyzed, among all gestations, the influence of chorionicity in CRLD and birthweight discordancy, obtaining p = 0.74 (> 0.05) and p = 0.06 (> 0.05), respectively. These results are displayed in Table 2.

Table 2
Influence of chorionicity type in crown-rump length discordancy (CRLD) and in birthweight discordancy (birthweight discordancy) (%)

Concerning the 2nd objective, we determined the association between CRLD and birthweight discordancy and analyzed the regression line of their association graph. Among all gestations, the correlation between CRLD and birthweight discordancy can be seen in Fig. 1, in which the regression line is defined by birthweight discordancy = 0.8864 x CRLD + 0.0743, with r2 = 0.1599, being r2 (coefficient of determination) the variation of birthweight discordancy explained by CRLD.

Fig. 1
Correlation between crown-rump length discordancy (CRLD) and birthweight discordancy (birthweight discordancy), among all gestations.

The same analysis was performed among MCs and DCs (Fig. 2). In MCs, the association graph had a regression line defined by birthweight discordancy = 0.7312 x CRLD + 0.0623, with r2 = 0.1763; and, in DCs, the association graph had a regression line defined by birthweight discordancy = 0.9438 x CRLD + 0,0787, with r2 = 0.1591, similar to the results showed among all gestations.

Fig. 2
Correlation between crown-rump length discordancy (CRLD) and birthweight discordancy (birthweight discordancy), among monochorionic and dichorionic gestations.

Concerning the 3rd objective, CRL discordancy and BW discordancy for both MC and DC were analyzed. According to the literature, discordancy in CRL ≥ 10% and, in BW, ≥ 15% was considered of major clinical importance. The results achieved showed that 7.58% of MCs showed a CRLD of at least 10%, against 13.56% among DCs. It was also verified that 16.67% of MCs had a birthweight discordancy of at least 15%, against 31.64% among DCs.

Discussion

No statistically significant differences for CRL and BW according to chorionicity were found, but a borderline, although non-statistically significant difference, was observed for BW. A similar situation was identified for the influence of chorionicity in birthweight discordancy and CRLD. This can be explained by an early developmental phase in which the CRL measurement is performed, and therefore the influence of chorionicity in fetal growth may not be noticeable until later in pregnancy when the BW is estimated. The fetal growth progression and the later phases of development will possibly allow for more biometric differences and diverse growth of the two fetuses when there are two placentas available (DCs). This first conclusion was compatible with the results found in the reviewed literature.11 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(01):66-69. Doi: 10.1111/1754-9485.12268
https://doi.org/10.1111/1754-9485.12268...
22 Mihailidis S, Bockmann M, McConnell E, et al. The influence of chorion type on health measures at birth and dental development in Australian and Dutch twins: a comparative study. Twin Res Hum Genet. 2015;18(04):368-374. Doi: 10.1017/thg.2015.43
https://doi.org/10.1017/thg.2015.43...
33 Kyono K. The precise timing of embryo splitting for monozygotic dichorionic diamniotic twins: when does embryo splitting for monozygotic dichorionic diamniotic twins occur? Evidence for splitting at the morula/blastocyst stage from studies of in vitro fertilization. Twin Res Hum Genet. 2013;16(04):827-832. Doi: 10.1017/thg.2013.32
https://doi.org/10.1017/thg.2013.32...
44 Farah N, Hogan J, Johnson S, Stuart B, Daly S. Prospective risk of fetal death in uncomplicated monochorionic twins. Acta Obstet Gynecol Scand. 2012;91(03):382-385. Doi: 10.1111/j.1600- 0412.2011.01288.x
https://doi.org/10.1111/j.1600-...
55 Oldenburg A, Rode L, Bødker B, Holmskov A, Jørgensen FS, Larsen H, et al. Influence of chorionicity on perinatal outcome in a large cohort of Danish twin pregnancies. Ultrasound Obstet Gynecol. 2012;39(01):69-74. Doi: 10.1002/uog.10057
https://doi.org/10.1002/uog.10057...
66 Glinianaia SV, Obeysekera MA, Sturgiss S, Bell R. Stillbirth and neonatal mortality in monochorionic and dichorionic twins: a population-based study. Hum Reprod. 2011;26(09):2549-2557. Doi: 10.1093/humrep/der213
https://doi.org/10.1093/humrep/der213...
1010 Carroll SG, Tyfield L, Reeve L, Porter H, Soothill P, Kyle PM. Is zygosity or chorionicity the main determinant of fetal outcome in twin pregnancies? Am J Obstet Gynecol. 2005;193(3 Pt 1):757-761. Doi: 10.1016/j.ajog.2005.01.024
https://doi.org/10.1016/j.ajog.2005.01.0...
2323 Blickstein I, Mincha S, Goldman RD, Machin GA, Keith LG. The Northwestern twin chorionicity study: testing the 'placental crowding' hypothesis. J Perinat Med. 2006;34(02):158-161. Doi: 10.1515/JPM.2006.028
https://doi.org/10.1515/JPM.2006.028...
Maybe in future studies with a larger sample, this influence of chorionicity in BW and birthweight discordancy will become more apparent.

Among all gestations, nearly 16% of the birthweight discordancy is correlated to CRLD. Among MCs, nearly 18% of the birthweight discordancy is correlated to the CRLD, not very different from what happens in DCs, in which nearly 16% of the BWD is correlated to the CRLD. BWD may be correlated in this present extension to CRLD, but not really explained by it since other variables were not studied. So, it would be interesting in future studies to clarify the other putative determinants that could explain ∼ 80% of the birthweight discordancy other than CRLD, which only seems to account for nearly 20%. This second conclusion was matched with the results found by other authors, such as Grande et al.3232 Grande M, Goncé A, Stergiotou I, Bennasar M, Borrell A. Intertwin crown-rump length discordance in the prediction of fetal anomalies, fetal loss and adverse perinatal outcome. J Matern Fetal Neonatal Med. 2016;29(17):2883-2888. Doi: 10.3109/14767058. 2015.1107901
https://doi.org/10.3109/14767058...

There is a higher percentage of discordancy in CRL ≥ 10% in DCs (13.56%) than in MCs (7.58%). Regarding the BW discordancy, there is also a greater percentage of major and clinically relevant discordancy in DCs (31.54%) than in MCs (16.67%). This third conclusion was contradicted by the reviewed literature, being necessary some other studies to clear up this point.2828 Lopriore E, Pasman SA, Klumper FJ, Middeldorp JM, Walther FJ, Oepkes D. Placental characteristics in growth-discordant monochorionic twins: a matched case-control study. Placenta. 2012;33 (03):171-174. Doi: 10.1016/j.placenta.2011.12.004
https://doi.org/10.1016/j.placenta.2011....
Moreover, pathological cases with selective intrauterine growth restriction were one of the exclusion criteria of the present study, and this is probably one of the reasons why birthweight discordancy is greater in dichorionic pregnancies. Therefore, care should be taken in the generalization of this conclusion by the analysis of the data collected.

The present study had some possible limitations, such as the intraobserver and interobserver variability in the measurements of the biometric parameters, since CRL and BW measurements were performed by different certified health professionals, as well as the limitation related to the sample length, which should be larger in future studies to clarify the influence of chorionicity in later stages of twin pregnancies. Moreover, the statistical analysis would be more interesting if applied in the future in a prospective study, accompanying the twin pregnancies until the birth of the babies or even trying to go forward perceiving the later consequences of the birthweight discordancy.

As strengths, the present study raises the issue of the possible influence of chorionicity in twins' growth and the future consequences of birthweight discordancy and CRLD in the potential of fetal growth according to the type of placentation.

Conclusion

According to the main objectives of the present study, no statistically significant influence of chorionicity could be identified in both BW and birthweight discordancy, as well as in CRL and CRLD. Nevertheless, birthweight discordancy was explained in nearly 20% by the influence of CRLD. This findings should let all the health providers aware of the main importance of strict and precocious twin pregnancies' surveillance to prevent any disturbance of fetal growth and development.

Acknowledgments

I wish to thank all of those who contributed to the completion of this study,meaning families, friends, health professionals and the Board of Directors of the Centro Hospitalar S. João.

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Publication Dates

  • Publication in this collection
    23 Oct 2020
  • Date of issue
    Sept 2020

History

  • Received
    09 June 2019
  • Accepted
    02 Apr 2020
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