ORIGINAL ARTICLE Confined placental mosaicism at chorionic villous sampling: risk factors and pregnancy outcome Giulia Maria Baffero 1,2 *, Edgardo Somigliana 1 , Francesca Crovetto 1,2 , Alessio Paffoni 1 , Nicola Persico 1,3 , Silvana Guerneri 1 , Faustina Lalatta 1 , Roberto Fogliani 1 and Luigi Fedele 1,2 1 Fondazione Cà Granda, Ospedale Maggiore Policlinico, Milan, Italy 2 Università degli Studi di Milano, Milan, Italy 3 Fondazione Giorgio Pardi, Milan, Italy *Correspondence to: Giulia Maria Baffero. E-mail: giulia.baffero@gmail.com ABSTRACT Objective This study aims to investigate the clinical relevance of confined placental mosaicism (CPM) detected at chorionic villous sampling (CVS) and to identify risk factors for this condition. Method Women diagnosed with CPM between January 2005 and December 2009 were identified. They were matched to women with unremarkable CVS in a 1 : 2 ratio by study period and contacted by phone for interview. Results One hundred fifteen exposed and 230 unexposed women were selected. Baseline characteristics did not differ between the study groups apart from maternal body mass index, which is mildly higher in the CPM group (+0.6 kg/m 2 , p = 0.047), and maternal age, which is higher in women with type III CPM (39.7  2.6 vs 37.1  3.2 years, p = 0.005). A higher frequency of gestational hypertension was observed in exposed women (10% vs 2%) (p = 0.003). Small for gestational age newborns were more frequent in women with type I CPM (15% vs 5%, p = 0.03). The incidence of other main complications of pregnancy (stillbirth, prematurity, preeclampsia and gestational diabetes mellitus) was similar. Neonatal complications and subsequent infant health and development did not also differ. Conclusion Women with the diagnosis of CPM at CVS can be generally reassured regarding the course of pregnancy and infant health and development. © 2012 John Wiley & Sons, Ltd. Funding sources: None Conflicts of interest: None declared INTRODUCTION In most pregnancies, the fetus and the placenta have an identical chromosomal complement because they originate from the same zygote. However, in approximately 1% to 2% 1,2 of chorionic villous sampling (CVS) performed between 9 and 12 weeks’ gestation, there is a cytogenetic abnormality confined to the placental tissue. This situation, known as confined placental mosaicism (CPM), is better defined as a dichotomy between the chromosomal constitution of placental tissue of extraembryonic origin and embryonic/ fetal tissues, where the placenta presents a cellular line with a numerical or structural abnormality whereas the fetus has a normal chromosomal complement. Two different types of CPMs have been described: mitotic and meiotic. In mitotic CPM, the conception is diploid, and the abnormal division takes place in the progenitors of specific placental cell lineages. In contrast, in meiotic CPM, the zygote has an initial abnormal chromosomal complement (most often a trisomy), and a subsequent mitotic ‘error’ causes the loss of the abnormal chromosome in the true embryonic cell lineage, leaving the abnormal cell line confined to the placenta, a process known as trisomic zygote rescue. 3–5 The presence of an abnormal cell line in placental tissues continues to present a clinical dilemma. Some authors have found an association between CPM and pregnancy loss, 6–11 intrauterine fetal growth restriction (IUGR) 12–16 and higher incidence of pregnancy-induced hypertension (PIH), 17–20 whereas other studies failed to confirm these findings. 14,21–23 In fact, despite a large body of literature on CPM, controlled studies aimed at investigating pregnancy outcome in women carrying affected pregnancies are surprisingly few, under-powered and controversial. 9–11,14,23,25,26 Results from these studies are summarized in Table 1. Moreover, the identification of risk factors for CPM has received extremely scanty attention. Only a minority of studies report on this point, and evidence mainly focuses on maternal age, mode of conception and obstetrical history. 9,11,24,27,28 To further elucidate the clinical relevance of CPM, we set up a matched cohort study aimed at assessing pregnancy and neonatal outcome of pregnancies with a diagnosis of CPM. Prenatal Diagnosis 2012, 32, 1- 7 © 2012 John Wiley & Sons, Ltd. DOI: 10.1002/pd.3965