Clinical Significance of Non-Invasive Prenatal Screening for Trisomy 7: Cohort Study and Literature Review

Abstract

Trisomy 7 is the most frequently observed type of rare autosomal trisomies in genome-wide non-invasive prenatal screening (NIPS). Currently, the clinical significance of trisomy 7 NIPS-positive results is still unknown. We reviewed two independent cohorts from two laboratories where similar NIPS metrics were applied. A total of 70,441 singleton cases who underwent genome-wide NIPS were analyzed, among which 39 pregnancies were positive for trisomy 7, yielding a screen-positive rate of 0.055% (39/70,441). There were 28 cases with invasive testing results available; the positive predictive value (PPV) was 3.6% (1/28). We then searched the published NIPS studies to generate a large cohort of 437,873 pregnancies and identified 247 cases (0.056%) that were screened positive for trisomy 7. The overall PPV was 3.4% (4/118) in the combined data. The presence of uniparental disomy 7 was not detected in the NIPS trisomy 7-positive pregnancies with normal fetal karyotype. Among the 85 cases with pregnancy outcome available in combined data, 88.2% were normal live births, 14.1% had intrauterine growth restriction, preterm birth or low birth weight, 3.5% presented with ultrasound abnormality, and no fetal loss was observed. Our data provide valuable information for counseling and management of trisomy 7-positive NIPS pregnancies.

Systematic evidence-based review: The application of noninvasive prenatal screening using cell-free DNA in general-risk pregnancies

“…Several recent reviews and meta-analyses have been published on NIPS. 4,[58][59][60][61][62] Compared with traditional screening, the 2019 health technology assessment by Health Quality Ontario determined that NIPS was effective in a general or average-risk population to screen for T21, T18, and T13. 58 Our results similarly show the high performance of NIPS to screen for the common trisomies in a general population.…”

Pregnancy outcomes of rare autosomal trisomies results in non‐invasive prenatal screening: clinical follow‐up data from a single tertiary centre

“…T7 is the most common RAT, with a rate of 0.056% among NIPS examinations, and has a mostly favourable outcome 20 . Zhu et al 20 reviewed 85 cases of T7 detected by NIPS.…”

“…T7 is the most common RAT, with a rate of 0.056% among NIPS examinations, and has a mostly favourable outcome 20 . Zhu et al 20 reviewed 85 cases of T7 detected by NIPS. Among them, 88.2% were live births with a normal outlook; 14.1% had intrauterine growth restriction, preterm birth or low birth weight; 3.5% presented with ultrasound abnormalities; and no fetal loss was observed.…”

Prenatal diagnosis of trisomy 8 mosaicism, initially identified by cffDNA screening

“…Even though RATs are in majority of cases restricted to placenta, cases like the present one can also be among those being detected by NIPT. Their detection could help omitting increased risk of miscarriage, intrauterine growth restriction [ 23 , 24 ], low birth weight [ 25 ], small-for-gestational-age infants [ 26 ], uniparental disomy [ 22 ] and neonatal intensive care unit admission [ 27 ]. Therefore, early identification of RATs is helpful to control risks of adverse pregnancy outcomes [ 28 ].…”