Haemoglobin differences at birth in monochorionic twins without chronic twin-to-twin transfusion syndrome

To determine the haemoglobin (Hb) differences at birth in monochorionic (MC) twins without chronic twin-to-twin transfusion syndrome (TTTS) in relation to birth order and placental vascular anatomy.

All consecutive cases of MC twins without chronic TTTS and dichorionic (DC) twins delivered at our centre and admitted to our neonatal nursery between June 2002 and December 2004 were included in our study. We analysed Hb differences at birth and on day 2, in relation to birth order and placental vascular anatomy.

Forty-five pairs of MC twins and 71 pairs of DC twins were included. Mean Hb differences at birth in MC and DC twins were similar, respectively 1.5 and 1.4 g/dL. Hb differences >5 g/dL at birth were found in 2% (1/45) of MC twins compared to 8% (6/71) in DC twins. On day 2, mean Hb differences in MC twins increased to 3.8 g/dL, and the rate of MC twins with Hb differences >5 g/dL increased to 27% (12/45) (p < 0.001). Mean Hb differences and the percentage of twins with Hb differences >5 g/dL in DC twins did not change on day 2. In MC twins, Hb levels measured on day 2 were significantly higher in second-born twins than in first-born twins, respectively 17.7 and 15.5 g/dL (p = 0.002). Hb differences on day 2 were significantly higher in MC twins with superficial vascular anastomoses than those without superficial anastomoses, respectively 4.0 g/dL and 1.5 g/dL (p = 0.036).

Hb differences occur more frequently in MC twins without chronic TTTS than in DC twins, but only when measured on the second day of life. Hb differences in MC twins are associated with birth order and superficial vascular anastomoses.