Non Immune Fetal Hydrops (FH) caused by Parvovirus B19 in one dichorionic-diamnotic (DCDA) twin has been reported but remains extremely rare.1 2 We describe FH affecting one twin in a DCDA pregnancy. The mother was 26 years old in her 4th pregnancy. Her blood group was A Rhesus positive. Ultrasound scan at 20+5 gestation confirmed FH in one twin with no structural abnormality. Middle cerebral artery peak systolic velocity (MCA PSV) was elevated at 43.0cm/s (>1.55MOM).3 Ultrasound assessment of the second twin confirmed normal anatomy with no evidence of FH. Findings suggested FH secondary to anaemia in only one twin. Assessment followed in the tertiary centre with subsequent amniocentesis and intrauterine blood transfusion at 21+0. Pre-transfusion haemoglobin (Hb) was 4.6g/dl. 15ml of 75% donor blood was transfused with post-transfusion Hb of 11.4g/dl. Maternal serology was positive for Parvovirus B19 specific immunoglobulin (IgM). Ultrasound confirmed resolution of FH and normal MCA PSV by 24+4. Growth of the affected twin remained below the 10th centile while the second twin's growth was appropriate for gestation. Caesarean section was performed in early labour at maternal request at 35+4, birth weights were 1790g and 2460g. Parvovirus B19 is a major cause of non-immune FH and responsible for 15-20% of cases within the United Kingdom.4 Trans-placental passage rates approach 25%4 but the incidence of FH is about 4%.5 Maternal viral load, gestation and immune responses influence fetal infection rates however the exact mechanism for discordant FH in DCDA pregnancies remains unclear.