Skip to main content
SMFM 2025 Pregnancy Meeting Main banner
Final Program


Program Book
Icon Legend
Presentation Icons
Additional registration fee required
Additional registration fee required
CME Credit Offered
CME Credit Offered
Abstract Award
Abstract Award
Recording
Recording
Poster Icons
Additional registration fee required
Additional registration fee required
Faculty have requested this content not be shared on social media
Faculty have requested this content not be shared on social media
CME Credit Offered
CME Credit Offered
Abstract Award
Abstract Award

Oral Plenary Session 1

Oral Plenary Session 1

(3) Fetal fraction amplification enables accurate prenatal cell-free DNA screening at 8 weeks gestation

Thursday, January 30, 2025
8:30 AM - 8:45 AM  
Location: Aurora Ballroom, Lobby Level
Abstract Award
Objective: Cell-free DNA (cfDNA) screening for fetal aneuploidy is typically offered beginning at 10 weeks’ gestation. Prior to 10 weeks the proportion of placental cfDNA, known as the fetal fraction (FF), is often too low to allow for confident analysis. FF amplification, the preferential enrichment of placental cfDNA based on its shorter fragment size, may sufficiently increase FF to enable screening earlier than 10 weeks with high confidence and a low failure rate. This study aimed to evaluate the feasibility of cfDNA screening using FF amplification prior to 10 weeks’ gestation.

Study Design: Blood samples were collected from pregnant patients with singleton gestations at 6w0d-9w6d and ≥10w0d. Samples were processed using an approach that incorporates FF amplification. Logistic regression was used to evaluate the proportion of samples with low FF (< 4%) as a function of gestational age (GA). Aneuploidy and sex-call concordance were evaluated.

Results: 459 patients completed both blood draws. Additional cohort characteristics are described in the Table. FF ranged from 2.1- 34.7%, with lower GAs corresponding to lower FFs (Figure). Prior to the incorporation of FF amplification, 4.78% of samples at 10w0d had a low FF (< 4%). FF amplification allowed for comparable performance at 7w3d (the earliest date where < 4.78% of samples had FF < 4%). To reflect practical application in a clinical setting, we selected 8w0d through 9w6d as the “early GA” period. Among the 239 samples in the early GA period, one sample failed because of insufficient FF (FF=2.5%), yielding a no-call rate of 0.42%. Three trisomies (two T21 and one T7) were identified in the early GA period, and each was concordant with the corresponding ≥10w0d call. All 238 passing samples had concordant sex calls in the early GA and ≥10w0d GA periods.

Conclusion: CfDNA screening using FF amplification provided accurate results as early as 8 weeks GA with a low no-call rate in this study population. Earlier prediction of risk for chromosomal abnormalities may provide patients with the option to have diagnostic testing with CVS at 10 weeks’ gestation.