Outcomes in pregnancies with a confined placental mosaicism and implications for prenatal screening using cell-free DNA

Purpose: To assess the association between confined placental mosaicism (CPM) and adverse pregnancy outcome. Methods: A retrospective cohort study was carried out evaluating the outcome of pregnancies with and without CPM involving a rare autosomal trisomy (RAT) or tetraploidy. Birthweight, gestational age at delivery, fetal growth restriction (FGR), Apgar score, neonatal intensive care admission, preterm delivery, and hypertensive disorders of pregnancy were considered. Results: Overall 181 pregnancies with CPM and 757 controls were recruited. Outcome information was available for 69% of cases (n = 124) and 62% of controls (n = 468). CPM involving trisomy 16 (T16) was associated with increased incidence of birthweight <3rd centile (P = 0.007, odds ratio [OR] = 11.2, 95% confidence interval [CI] = 2.7–47.1) and preterm delivery (P = 0.029, OR = 10.2, 95% CI = 1.9–54.7). For the other RATs, an association with prenatally diagnosed FGR was not supported by birthweight data and there were no other strong associations with adverse outcomes. Conclusion: Excluding T16, the incidence of adverse pregnancy outcomes for pregnancies carrying a CPM is low. RATs can also be identified through genome-wide cell-free DNA screening. Because most of these will be attributable to CPMs, we conclude that this screening is of minimal benefit.