Iron metabolism in monochorionic twin pregnancies in relation to twin--twin transfusion syndrome

Fetal iron metabolism was investigated in monochorionic (MC) twin pregnancies in relation to twin-twin transfusion syndrome (TTTS). Matched maternal and fetal blood samples were obtained both in utero and at birth from MC twins with TTTS (n = 23) and without TTTS (n = 18). In a second group of 30 twin pairs (15 with and 15 without TTTS), liver iron content was assessed by using archived paraffin wax-embedded blocks. Serum ferritin was determined by radioimmunoassay and values are given as gestation independent Z-scores and expressed as mean with 95% confidence intervals. Ferritin concentrations in the recipients were higher than in the donors both in utero (P < 0.01) and at birth (P < 0.01). Fetal serum ferritin in non-TTTS twins were similar to the recipient twins but higher than the donor twins (P < 0.05). A significant association was found between ferritin concentrations, the total red blood cell count and haemoglobin in the TTTS twin pairs (P < 0.01) and the non-TTTS twins as a group (P < 0.01). The total stainable liver iron was comparable between twin pairs in the TTTS and non-TTTS groups. This study fails to provide evidence of iron overload in the recipient and depletion in the donor twins and, thereby, questions the validity of the conventional theory of inter-twin transfusion as the cause of TTTS.