Haematological indices at fetal blood sampling in monochorionic pregnancies complicated by feto-fetal transfusion syndrome.

36 MCDA twin pregnancies with FFTS investigated by fetal blood sampling (FBS) were studied over a 10-year period (1988-1997). The haematological data obtained at FBS were compared between the donor and recipient fetuses. It was shown that the donor fetus had a significantly lower haematocrit (35.7 per cent versus 47.2 per cent; p < 0.001), haemoglobin (12.2 g/dl versus 15.8 g/dl; p < 0.001), and red blood cell count (2.9 x 10(12)/l versus 3.8 x 10(12)/l; p = 0.006) compared with the recipient fetus. A haematocrit discordancy of > 15 per cent, however, was found in only 25 per cent of twin pairs. There were no significant inter twin differences in the remaining indices. The study concluded that although there are significant differences in haematocrit and red cell mass between the donor and recipient fetuses, only a minority of fetuses will have degrees of discordancy suggested in the literature to be diagnostic. We suggest that FBS does not have a role in establishing the diagnosis of FFTS, although its role in determining the degree of haematocrit discordancy to assist in timing of delivery remains to be evaluated.