Placental Histological Changes

Placental Histological Changes associated with Twin–Twin Transfusion Syndrome

The portion of the placenta supporting the donor fetus is usually pale. This is in stark contrast to the recipient’s placental portion, which is congested, giving an enlarged and hyperemic appearance. However, at the level of the villi, the donor has been described as having a significantly enlarged villous structure compared with that of the recipient,47 and this has been attributed to fetal edema of the donor villi (Figure 5.11). 

This finding is unexpected in that fetal edema of the donor fetus is uncommon, particularly relative to the recipient twin. The enlarged villi of the donor fetus may in turn impinge on the intervillous space, thus affecting maternal perfusion. 48 This may explain the observations made by Matijevic et al, who studied blood flow in the spiral arteries of each twin’s portion of the placenta using Doppler. 

They reported increased resistance on the side of the donor or growthrestricted twin compared with that of the recipient or appropriately grown twin.49 Sala et al50 reported that the recipient twin had thinned trophoblastic villous covering and that the villous vessels were markedly distended. In contrast, the donor had thick trophoblast and frequently ‘empty’ villous capillaries. These observed histological differences between the donor and recipient twins may have an understated role in TTTS, particularly as it relates to the further propagation of the disease. 

CONCLUSION 

To better understand TTTS, the study of the placenta must continue. Friedrich Schatz and others were instrumental in making the first steps in our understanding of TTTS by methodical evaluation of the placenta after delivery. Yet, there is only so much that can be learned from a non-functioning organ – one that is neither linked to the maternal nor fetal circulations. As technology advances, it is our hope that the placenta may be studied more frequently in utero. Only after viewing the placenta ‘in action’ will we be able to take the next few steps in our understanding of TTTS.