Nonpresenting Dichorionic Twins and Placental Vascular Malperfusion

Area of Science:

• Obstetrics and Gynecology
• Perinatal Medicine
• Reproductive Biology

Background:

• Dichorionic twins often exhibit differences in birth weight between cotwins.
• The nonpresenting twin is typically smaller, but the underlying causes require further investigation.
• Placental pathology is a suspected contributor to discordant growth in twin gestations.

Purpose of the Study:

• To investigate the association between placental pathology and the reduced birth size of nonpresenting dichorionic twins.
• To determine if specific placental lesions mediate the size discrepancy between dichorionic twins.
• To test the hypothesis that placental abnormalities significantly contribute to smaller birth size in nonpresenting dichorionic twins.

Main Methods:

• Retrospective cohort study of 1,322 dichorionic twin deliveries (2002-2015).
• Routine pathological examination of all placentas from multifetal gestations.
• Classification of placental abnormalities (maternal vascular malperfusion, fetal vascular malperfusion, hemorrhage, villitis) and comparison between presenting and nonpresenting twins.

Main Results:

• Nonpresenting twins were smaller from 32 weeks gestation (2,224g vs 2,278g, P=.036).
• Nonpresenting twins had smaller placentas (361g vs 492g, P<.001) detected as early as 24 weeks.
• Higher odds of placental abnormality (aOR 1.91) and maternal vascular malperfusion (aOR 2.75) were observed in nonpresenting twins.

Conclusions:

• Lower birth weight in nonpresenting dichorionic twins is correlated with increased placental maternal vascular malperfusion.
• Selective placental pathology, particularly maternal vascular malperfusion, significantly contributes to the smaller size of nonpresenting dichorionic twins.
• These findings highlight the importance of placental examination in understanding discordant growth in twin pregnancies.