Cord blood samples should be taken at delivery. The DAT may be positive, but is not a useful indication of severity or need for therapy. The best simple criterion of severity is the cord Hb level;
indicate fetuses with moderate or severe anaemia (< 0.65 multiples ofthe median Hb concentration). The solid circles indicate the fetuses with hydrops. The solid curve indicates the median peak systolic velocity in the middle cerebral artery and the dotted curve indicates 1.5 multiples ofthe median (courtesy of Professor Charles Rodeck).
this is much more useful than a sample taken a few hours after birth, when rapid haemodynamic changes are occurring. The normal range of cord Hb levels is 13.6-19.6 g/dL. Most infants with levels in this range do not require therapy; more than 50% of affected babies have a level in the normal range. Where the cord Hb is below 12 g/dL, exchange transfusion will be necessary. It may also be indicated for a rising bilirubin level after birth, dependent upon the rate of rise and the maturity of the infant. Phototherapy may be given to reduce the rise in bilirubin levels but it is not a substitute for transfusion. Less severely affected infants may require small-volume transfusions of red cells at 2-3 weeks of age. In both of these instances, careful follow-up arrangements must be made as haemolysis may
continue, causing further rises in bilirubin or need for additional top-up transfusion.
The infant's RhD group should be determined on the cord blood sample of all infants born to D-negative mothers with no preformed anti-D, to give anti-D Ig prophylaxis if they type as D-positive. A DAT is only performed on cord bloods of mothers who have made anti-D; the cord bloods of women given antenatal Rh prophylaxis should not have a DAT done as it may be positive due to the passive anti-D given. If intrauterine transfusions have been given, the ABO and Rh groups may be those of the donor, and the DAT may be negative. A DAT should be performed on the cord blood of all women who have IAT-reactive antibodies. If the DAT is positive, the cord Hb should be checked and the clinical state, Hb and bilirubin of the infant monitored for signs of HDN for 1 month.
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