Placental weight in pregnancies with trisomy confined to the placenta.

Objective: Mosaicism with trisomy confined to the placenta is present in ~1% of ongoing pregnancies at the time of chorionic villus sampling. Some studies have found reduced fetal growth in confined placental trisomy. The objective of this study was to assess placental weight and feto-placental weight ratio in pregnancies with trisomy confined to the placenta, and to correlate them with the level of trisomy in the three major placental lineages.

Methods: We conducted a retrospective study of 69 pregnancies with prenatally diagnosed mosaic trisomy in which the trisomic cells were confined to the placenta. Placental weight and feto-placental weight ratio were compared to those of matched controls, and placental weight was also analyzed for associations with the type and level of trisomy. Placental pathology was also reviewed.

Results: The pregnancies with mosaic trisomy were found to have lower placental weights than matched controls, but normal feto-placental weight ratios. Placental weight was not associated with the type or level of trisomic cells in the three placental lineages at term (chorionic plate, chorionic villus mesenchyme, and trophoblast). There were no pathognomonic findings on routine placental pathology of the trisomic placentas.

Conclusion: Although placental weight was reduced (with normal feto-placental weight ratio) in pregnancies with trisomy confined to the placenta, the level of placental trisomy was not correlated with placental weight. Thus, trisomy may alter placental function rather than have a direct hypoplastic effect on placental growth. More in-depth studies beyond routine pathology are required to identify how trisomy affects placental function.