Capillary malformation–arteriovenous malformation (CM–AVM) is a newly recognized clinical entity caused by mutation of the RASA1 gene, which encodes p120-RasGAP. Here we describe, for the first time, a patient with CM–AVM presenting during the late stages of pregnancy with pulmonary “capillary level” microvascular shunt, worsening cutaneous capillary malformations, and gross fluid overload. Sequencing revealed a novel mutation of the RASA1 gene involving a frameshift mutation in the RASGAP domain of RASA1. This report extends our current genetic and clinical understanding of CM–AVM. © 2013 Wiley Periodicals, Inc.