Intrathoracic fluid may be a normal finding at around 8 gestational weeks

Objective To describe the observation of embryonic thoracic fluid at around 8 weeks gestation and to discuss the likely etiology. Methods This was a retrospective study of patients referred between August 2005 and May 2006 to our units in France and in the USA for a dating scan between 6 and 10 weeks. Included in our series were all embryos presenting with an ultrasound finding suggestive of an early pericardial fluid collection, i.e. a large anechoic fluid collection surrounding the heart. The gestational age, fetal heart rate and maternal age at this first scan were recorded along with nuchal translucency thickness as measured at the 12-week scan and the second-trimester anomaly scan results. Results Five cases were included in this study. In all five patients, the anechoic fluid collection was visualized at 8 weeks, and by the time of the nuchal scan it had disappeared completely. The nuchal translucency thickness was normal in all cases and all five embryos had normal cardiac examinations during the second trimester and were normal at birth. Conclusions The observation on ultrasound at 8 weeks' gestation of a large anechoic fluid collection surrounding the heart that disappears by week 12 is suggestive of a transient pericardial collection. Copyright (c) 2007 ISUOG. Published by John Wiley & Sons, Ltd.