(464) Fetal fraction from cfDNA among placenta accreta spectrum, placenta previa, and normal placentation

Disorders of placental morphogenesis have been associated with differences in the amount of trophoblastic DNA shed into the maternal circulation, thereby impacting the reported fetal fraction percentages from cfDNA testing. We aimed to determine the difference in FF from cfDNA in PAS, previa, and normal placentation.

Study Design:

We conducted a retrospective matched cohort study comparing FF from cfDNA testing in patients who had histologically confirmed PAS with and without PP, PP without PAS, and normal controls. Patients were identified based on diagnosis codes, ultrasound confirmation of PP, histology confirming presence of absence of PAS and cfDNA testing with reported FF. Controls were matched to cases 2:1 by gestational age at cfDNA testing and maternal BMI. Multiple gestations and pregnancies with chromosomal abnormalities were excluded.

Results:

There were no significant differences in mean FF from cfDNA between PAS without PP (n=19) and controls, and PAS with PP (n=13) and controls. There was a significant difference in FF between Previa without PAS and controls (10.1% vs 7.9%, p=0.014) and all cases with Previa including PAS+PP and controls (10.1% vs 7.9%, p=0.013). There was no difference in FF between PAS with PP and Previa without PAS. There was also no significant difference between PAS with PP and PAS without PP.

Conclusion:

While all cases with placenta previa including those with PAS showed higher mean FF than controls, this is suspected to be driven by the previa component and not the presence of PAS given the significantly higher mean FF demonstrated in previa without PAS. Given the relatively recent use of routine cfDNA for prenatal genetic screening, a larger study of patients with PAS and cfDNA testing is needed to make conclusions about the clinical significance of fetal fraction in differentiating placenta previa with PAS from isolated placenta previa.