Factors associated with common and atypical chromosome abnormalities after positive combined first-trimester screening in Chinese women: a retrospective cohort study

Table 1 Prevalence of chromosomal abnormalities after cell-free DNA (cfDNA) testing, invasive prenatal diagnosis (IPD) alone, and birth in singleton pregnancies following positive conventional screening results; n (%)

	cfDNAtesting n = 752	IPD alone n = 986	No further test n = 117	Total
cfDNA testing	752	0
Abnormal results	24 (3.2%)	–
IPD or karyotyping after birth^c	34 (4.5%)^a	986(100.0%)	7 (6.0%)^c
Chromosome abnormalities	21 (2.8%)	120 (12.2%)	7 (6.0%)	148
Trisomy 21	14 (1.9%)	59 (6.0%)	2 (1.7%)	75
Trisomy 18 or 13	3 (0.4%)	22 (2.2%)	4 (3.4%)	29
Sex chromosome aneuploidy	2 (0.3%)	9 (0.9%)	–	11
Mosaicism	0 (0%)	10 (1.0%)	–	10
Other atypical abnormalities	1 (0.1%)	10 (1.0%)	1 (0.9%)^d	12
Balanced translocation	0 (0%)	10 (1.0%)	–	10
Unknown^b	1 (0.1%)	0 (0%)	–	1

^aOf 34 IPD, 24 were performed for abnormal cfDNA testing and 10 for anxiety, despite a negative cfDNA testing and normal scan findings.
^bpregnancy was terminated at another hospital.
^cKaryotyping (a) after birth in the group of women who declined further testing because they would keep their pregnancies anyway or worried about the IPD-related risk of miscarriage or (b) after miscarriage.
^dKaryotyping of a placental sample after spontaneous miscarriage showed 47,XX,+mar

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