PRENATAL DIAGNOSIS Prenat Diagn 2011; 31: 496–499. Published online 4 March 2011 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/pd.2726 Prenatal diagnosis and natural history of fetuses presenting with pleural effusion Rodrigo Ruano 1,2 *, Alan Saito Ramalho 1 , Ana Karina Silva Cardoso 1 , Kenneth Moise Jr 2 and Marcelo Zugaib 1 1 Obstetrics Department, Faculty of Medicine, S˜ ao Paulo University, S˜ ao Paulo, Brazil 2 Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Baylor College of Medicine, and the Texas Children’s Fetal Center, Houston, TX, USA Objective To describe the natural history of fetuses presenting with pleural effusion. Methods Between January 2005 and December 2009 all fetuses diagnosed with pleural effusion were followed up. Fetuses were divided into three groups: I, isolated pleural effusion; II, associated structural anomalies but normal karyotype; and III, chromosomal anomalies. Univariate and multivariate analyses were performed to determine the association between prenatal ultrasound findings and perinatal death. Results Fifty-six fetuses were included in the study. Associated structural or chromosomal anomalies occurred in 75.0% (42/56) of cases. Bilateral pleural effusion and fetal hydrops were associated with each other (p < 0.01) and with perinatal death (p < 0.05). Multivariate analysis indicated that only the presence of associated abnormalities was a statistical determinant of perinatal death (OR, 3.56; 95% CI, 1.48–5.64; p < 0.01). Conclusion Fetal pleural effusion is often associated with other abnormalities, and this association has poor perinatal outcome. Copyright  2011 John Wiley & Sons, Ltd. KEY WORDS: fetal pleural effusion; fetal therapy; ultrasonography; non-immune hydrops; hydrothorax; pleuroam- niotic shunt INTRODUCTION Fetal pleural effusion or hydrothorax is a rare condition with an incidence of approximately 1 in 15 000 new- borns (Longaker et al., 1989). It occurs twice as often in male fetuses and is most frequently diagnosed in the second or early third trimester (Rustico et al., 2007). Prenatal diagnosis is made by the identification of an anechoic space surrounding the lungs with the major- ity of cases being bilateral. Unilateral fetal hydrothorax appears to occur more sporadically and is caused by a congenital malformation of the thoracic duct or the pul- monary lymphatic system (Rustico et al., 2007, Yinon et al., 2008). The natural history of fetal pleural effusion is difficult to predict with expected perinatal mortal- ity rates between 22 and 53% (Longaker et al., 1989; Weber and Philipson, 1992; Aubard et al., 1998; Klam et al., 2005). Predicting perinatal outcome is fundamen- tal to the selection of cases for fetal intervention or early delivery. The aim of this study is to report the natural history of fetal pleural effusion in untreated fetuses. A secondary aim is to describe the relationship between associated fetal abnormalities and perinatal outcome. *Correspondence to: Rodrigo Ruano, Obstetrics Department, Fac- ulty of Medicine, S˜ ao Paulo University, Rua Valentim Magalh˜ aes, 100, AP 52, S˜ ao Paulo, SP, Brazil. E-mail: rodrigoruano@hotmail.com PATIENTS AND METHODS Between January 2005 and December 2009, all fetuses with a prenatal diagnosis of pleural effusion, excluding those with immune fetal hydrops, were followed up in our Fetal Medicine Center. The majority of these patients were referred from a large geographic surrounding area and therefore the determination of the incidence of fetal pleural effusion was not possible. Prenatal data were prospectively collected and recorded in our database. The protocol was approved by the local Ethics Committee and all patients signed written informed consent. Fetal pleural effusion was diagnosed at the time of prenatal ultrasound when an anechoic (liquid accumula- tion) could be seen surrounding one or both fetal lungs in the fetal thorax. Fetal hydrops was defined as the pres- ence of subcutaneous edema and liquid accumulation in at least one fetal body cavity (pleural effusion, pericar- dial effusion, or ascites) or a fluid accumulation in two body cavities. All patients whose fetuses presented with pleural effu- sion underwent a detailed fetal ultrasonographic exami- nation and fetal karyotype by amniocentesis performed by a fetal medicine specialist. Additionally, a complete fetal echocardiogram was performed by a pediatric car- diologist. In this study, no fetuses had a thoracoamniotic shunt. Patients were then followed up in our prenatal care clinic and delivery occurred at our hospital when- ever possible. The following data were collected: Copyright  2011 John Wiley & Sons, Ltd. Received: 13 December 2010 Revised: 25 January 2011 Accepted: 29 January 2011 Published online: 4 March 2011