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Q&A

Genetics

Poster Session 4

(989) Maternal and ultrasound characteristics associated with persistence of cell-free DNA from a vanishing twin pregnancy

Wednesday, February 14, 2024
1:00 PM – 2:30 PM  
Location: Prince George's Exhibit Hall CDE, Lower Atrium Level
Objective:

Vanishing twins (VTs) occur in up to 30% of early twin pregnancies and are associated with increased fetal aneuploidy and challenges for aneuploidy screening in the living twin (LT). These include potential for inaccurate cell-free (cf)DNA results due to a persistent cfDNA signal from the VT for up to 15 weeks. We sought to identify maternal and ultrasound (US) characteristics associated with persistence of cfDNA from a VT.

Study Design:

Planned secondary analysis of data from a prospective study of VTs at 17 centers between August 2021 – February 2023 aimed to develop a cfDNA algorithm for the LT in pregnancies with a LT and a VT. Monochorionicity, use of a donor egg, or iatrogenic fetal demise were excluded. SNP-based cfDNA screening at ≥9 weeks’ gestation evaluated the presence of one or two distinct sets of fetal alleles (signals). Univariate analysis was used to compare maternal and US characteristics among patients with one fetal signal, two fetal signals, or no-call results. Multivariable logistic regression was used to account for confounding.

Results:

Of 101 VT pregnancies, 42 had 1 fetal signal, 49 had 2, and 10 could not be determined due to very low fetal fractions . Median maternal age was 34.4 years and 20% conceived with assistance (IVF, ovulation induction and/or intrauterine insemination). Median GA of the LT at VT diagnosis was 9.4 weeks and median GA at cfDNA screening was 13 weeks. A non-viable fetus was visible in 54 and an empty sac in 47 cases (Table 1). Detection of two signals was associated with increasing GA at VT diagnosis (aOR = 1.66; 95%CI 1.19-2.49), a visible non-viable fetus on US (aOR = 3.48, 95%CI 1.05-12.60) and assisted conception (aOR = 6.10; 95%CI 1.19-47.50).

Conclusion:

Persistence of a second fetal signal was present in approximately half of VT pregnancies in our study and was more common with assisted conception, VT diagnosis after 8 weeks’ gestation, cfDNA within 3 weeks of VT diagnosis, and a visible non-viable fetus on US. This information may be helpful in optimizing timing of cfDNA screening in pregnancies with a VT.