Placental apoptosis in discordant twins

Objective: To investigate placental apoptosis in discordant dichorial twins.

Methods: Placental samples were obtained from 7 third-trimester suitable twins. Discordancy was defined as a >25 per cent difference in newborn birth weight. Light microscopy using hematoxylin and eosin (H&E)-stained paraffin slides and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling (TUNEL) methods were used to confirm the incidence of apoptosis. Investigators were blinded to pregnancy outcome.

Results: Both methods revealed that the incidence of apoptosis in the placentas of the smaller fetuses was significantly higher than in placentas of the larger fetuses. The incidence of TUNEL-positive cells in the former was 1.4+/-0.26 per cent: this was significantly higher than the incidence of apoptosis in the placental specimens of the latter (0.9+/-0.07 per cent, P< 0.02 Wilcoxon rank test). The same results were obtained with H&E: the incidence of apoptosis detected in placentas from the former was 1.07+/-0.1 per cent compared to 0.72+/-0.08 per cent in those of the latter (P< 0.02 Wilcoxon rank test).

Conclusions: Despite similar environment conditions, placental apoptosis is increased in the smaller fetus and thus might play a role in discordancy between twins. Since increased placental apoptosis has also been found in singleton intrauterine growth restriction, this supports the hypothesis that the smaller twin is selectively growth restricted.