January 2021 · Volume 10 · Issue 1 Page 39 International Journal of Reproduction, Contraception, Obstetrics and Gynecology Bivar L et al. Int J Reprod Contracept Obstet Gynecol. 2021 Jan;10(1):39-43 www.ijrcog.org pISSN 2320-1770 | eISSN 2320-1789 Original Research Article The impact of chorionicity on maternal and fetal outcomes Leonor Bivar 1 *, Maria Casteleiro 1 , Rita Vasconcelos 1 , Ana Borges 1 , Cátia Abreu 1 , Isabel Reis 1 , Ricardo Sousa-Santos 2,3 INTRODUCTION Over the last 20 years, the number of multifetal pregnancies, including twin pregnancies, has increased significantly, representing approximately 3-4% of all pregnancies. 1,2 The increasing incidence is mainly due to delayed childbearing (associated with higher multiple birth rate) as well as to the use of assisted reproductive techniques (ART). 3-5 Dizygotic twins are more common than monozygotic twins, approximately 70 and 30 percent of twins, respectively (in the absence of the use of ART). 6 While the prevalence of monozygotic twin pregnancies is relatively stable worldwide at 3 to 5 per 1000 births, dizygotic twin pregnancies are influenced by different factors including heredity, ethnicity and maternal age. 6,4,7 ABSTRACT Background: Women carrying twin pregnancies receive extensive antenatal counselling on fetal risks, but less is known about whether the presence of two placentas confers dissimilar maternal risks. We pretend to determine the impact of chorionicity on the maternal and fetal outcome, evaluating the possibility of finding the association between complications and the presence of two placental masses. Methods: We conducted a retrospective observational cohort study of 550 twin pregnancies monitored at a level-3 hospital, between January 2004 and December 2018. Results: Of the 550 pregnancies, 419 (76.2%) were bichorionic and 131 (23.8%) were monochorionic. Caesarean delivery was more frequent in monochorionic group (70.2% vs. 61.8%, p=0.05). There were no statistically significant differences in the proportion of adverse maternal outcomes between bichorionic and monochorionic pregnancies, despite a trend towards higher proportions in bichorionic group. Regarding fetal outcomes, monochorionic twins were delivered earlier (mean gestational age of 34 +4 weeks vs. 35 +1 weeks, p=0.04) and the proportion of preterm delivery cases between 32 +0 and 36 +6 weeks was higher in monochorionic pregnancies (72.5% vs. 54.9%, p=0.002). Stillbirth of one or both twins was more frequent in monochorionic group (3.1% vs. 0.5%, p=0.03). Conclusions: The presence of two placental masses does not seems to confer an increase in maternal risks, despite a trend towards higher proportions of adverse outcomes in bichorionic pregnancies. However, monochorionicity is associated with an increase in fetal risks, particularly prematurity. Counselling and monitoring of bichorionic or monochorionic pregnancies may be identical with respect to maternal risks, but chorionicity should be considered when evaluating fetal risks. Keywords: Chorionicity, Fetal outcome, Maternal outcome, Twin pregnancy 1 Department of Gynaecology and Obstetrics, Hospital de Braga, Braga, Portugal 2 Department of Gynaecology and Obstetrics, Hospital Senhora da Oliveira, Guimarães, Portugal 3 Center for Health Technology and Services Research - CINTESIS, Porto, Portugal Received: 17 November 2020 Accepted: 16 December 2020 *Correspondence: Dr. Leonor Bivar, E-mail: leonorbivar@gmail.com Copyright: © the author(s), publisher and licensee Medip Academy. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. DOI: https://dx.doi.org/10.18203/2320-1770.ijrcog20205751