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.