(898) Weighing the options: a six-year single-center analysis of second no-call non-invasive prenatal testing results

Objective: While a low-risk Non-invasive Prenatal Screening (NIPS) can offer reassurance for expectant parents, a no-call result (NCR) can cause significant anxiety. A definitive result is not guaranteed with repeat NIPS and a second NCR may compound patient uncertainty. This study aims to inform clinical practice and counselling for patients who receive NCRs by analyzing the demographics and outcomes of NCRs over the past six years.

Study Design: This retrospective cohort study was conducted at a large obstetric hospital in Ireland, utilizing a SNP-based cell-free fetal DNA test. We identified NCRs through an integrated electronic healthcare record. Data were collected on all patients who received NCRs from November 2017 to January 2024.

Results: 10,025 NIPS were conducted with 376 of patients receiving an initial NCR (3.8%). The median gestational age at first NIPS draw was 10.4 weeks [IQR: 9.7,11.7] with no significant difference across weight groups (p=0.566). 354 (94%) underwent a second NIPS with a result yielded in 76% (n=269) and 85 patients (24%) receiving a second NCR. A significant difference was found in the distribution of second NCRs by weight (p=0.001), with 40% of patients in the > 90 kg group receiving a further NCR. Fetal fraction (FF) at second NIPS decreased significantly according to maternal weight, with a median FF of 6.5% [IQR: 4.3,10.0] in patients < 65kgs and a median FF of 3.1% [IQR: 2.5,4.3] in those > 90kgs (p=0.001). 24% of second NCRs (n=20) underwent invasive testing, with half of these pregnancies affected by fetal aneuploidy. Table 1 summarizes the trends in NCRs and FF according to maternal weight.

Conclusion:

Despite repeat NIPS often providing a definitive result following an initial NCR, our study shows a significant correlation between maternal weight above 90kgs and the likelihood of a second NCR. Given this 40% risk of a further NCR and the underlying risk of fetal aneuploidy, we recommend offering invasive diagnostic options following an initial NCR to provide certainty for this patient group.