PLACENTAL PATHOLOGY IN DISCORDANT TWINS

OBJECTIVE: The aim of this study was to evaluate placental abnormaliti es in relation to birth weight discordance in dichorionic and monochor ionic twins. STUDY DESIGN: The maternal charts and placental abnormali ties of 147 structurally normal twin pairs with cords labeled at deliv ery were reviewed. The placental weight belonging to each twin was det ermined by measuring the length, width, and thickness in each of the t wo placental disks. Placental weight, chorionicity, infarction, abrupt io placentae decidual vascular abnormality, villous fibrosis and hypov ascularity, chronic villitis, and intraplacental thrombi were also ass essed Birth weight was discordant if greater-than-or-equal-to 20%. The data were analyzed with chi2 and analysis of variance after log trans formation of skewed discordancy values. RESULTS: Of the 147 twin pairs , 99 were dichorionic and 48 monochorionic. Placental weights were kno wn for 91 dichorionic and 40 monochorionic twins. Of the lighter cotwi ns in dichorionic twin pairs 36.3% (33/91) belonged to the heavier pla centa, 49.5% (45/91) belonged to the lighter placenta, and 14.3% (13/9 1) had an equal share of the placental weight with the heavier sibling (p < 0.05). In 42.4% (42/99) the lighter dichorionic twin had more pl acental lesions than the heavier twin, in 38.4% (38/99) the same numbe r of lesions were present in both placentas, and in 19.2% (19/99) the heavier twin had more placental lesions. There was linear correlation between percent discordance and number of placental lesions in the lig hter twin. In dichorionic twins 18 of the 99 (18.1%) were discordant. In 77.8% (14/18) the lighter twin had more placental lesions than the heavier twin, in 16.7% (3/18) the number of lesions was the same in bo th, and in 5.6% (1/18) the heaver twin had one more lesion than the li ghter twin (p < 0.05). In monochorionic twins, regardless of birth wei ght discordance, no differences in placental abnormalities were observ ed. CONCLUSIONS: In dichorionic twins significant birth weight discord ance was attributable not to differences in placental weight but to a greater number of placental lesions in the lighter twin than in the he avier twin (p < 0.05). This did not hold true for monochorionic twins.