Maternal characteristics
From June 1, 2015 to June 30, 2019, a total of 45773 maternal blood samples from singleton pregnancies were collected in Maternity and Child Health Hospital of Anhui Province. In our study, the gestational age of pregnancy at the time of amniocentesis ranged from 12+ 0–26+ 6 and the maternal age ranged from 16–45 years, with the < 30 age group forming the majority (17449/45773, 38.12%). Among the 45773 cases of NIPT, there were 17421 cases of advanced maternal age (38.06%), 19820 cases with high or critical risk (43.30%), 503 cases of fetal structural abnormalities or soft markers by B-ultrasound (1.10%), 86 cases of increased NT (NT ≥ 3 mm) (0.19%) and 7943 cases of volunteering NIPT with applicable people or people with caution (17.35%).
Table 1
Maternal characteristics of pregnant women who underwent NIPT
Maternal age (years) | Number | Percent (%) |
< 30 | 17449 | 38.12 |
30–34 | 11403 | 24.91 |
35–39 | 14353 | 31.36 |
≥ 40 | 2568 | 5.61 |
Advanced maternal age(≥35 years old) | 16921 | 36.97 |
Gestational age at NIPT (weeks) | | |
< 12+ 0 | 0 | 0.00 |
12–15 | 4853 | 10.60 |
16–19 | 33066 | 72.24 |
20–23 | 6740 | 14.72 |
24–26 | 1037 | 2.27 |
> 26 | 77 | 0.17 |
Clinical features | | |
Advanced maternal age (age ≥ 35 years) | 17421 | 38.06 |
High or critical risk of serological screening | 19820 | 43.30 |
Fetal structural abnormalities or soft markers by B-ultrasound | 503 | 1.10 |
Increased NT | 86 | 0.19 |
Voluntary demand | 7943 | 17.35 |
Othera | 0 | 0.00 |
a Patients with interventional surgery contraindications: placenta previa, reoperative infection. |
The screening value of SCA detection by NIPT
The total cases of SCA abnormal results were 314, including 58 cases of true-positive, 85 cases of false-positive and 171 cases of unverified. 147 pregnancies received positive results for 45,X. Among them, 56 pregnancies underwent invasive prenatal testing (38.10%). 7 cases were found to be true-positive, with the PPV of 12.50%. The NIPT and karyotype analysis was fully concordant in 1 case with the increased NT of 7.0 mm, 6 cases were mosaic 45,X. Karyotype information was available for 29 out of 61 NIPT results for 47,XXX (47.54%). There were 16 cases of true-positive. The PPV of 47,XXX was 55.17%. For 35 out of 71 NIPT results of 47,XXY with prenatal diagnostic (49.30%), 25 cases were identified to be true-positive with the PPV of 71.43%. Of those 35 cases with positive NIPT screening results for sex chromosome abnormalities of 47,XYY, karyotype information was available in 13 cases (37.14%), 10 cases were confirmed as true-positive. The PPV of 47,XYY was 76.92% (see Table 2). Moreover, the proportion of sex chromosome trisomy and monosomy were highly different. Of those 167 cases with positive screening results for sex chromosome trisomy, 52 out of 80 NIPT results were confirmed to be true-positive detected by invasive prenatal testing (65.00%). For 56 out of 147 cases for sex chromosome monosomy with prenatal diagnosis, 7 cases were consistent with NIPT results (12.50%). Chi-square tests were carried out to examine the associations between sex chromosome trisomy and monosomy X. Statistical significance was observed between the two groups (χ2 = 16.166, P = 0.000).
The PPV of SCA detected by NIPT was 40.56% (58/143). The PPV of SCA in pregnant women with advanced age group (≥ 35 years) was 48.44% (31/64), in high or critical risk of serological screening group was 27.5% (11/40), in voluntary demand for NIPT group was 45.16% (14/31) and in increased NT group was the high up to 44.44% (4/9). To our knowledge, the incidence of SCA with high or critical risk of serological screening in pregnant women aged < 30 year age group was 51.16% (22/43), while in pregnant women aged 30–34 year age group was 48.65% (18/37). There were no statistical significance between two groups (P < 0.05). The incidence of SCA with increased NT in pregnant women aged < 30 year age group and 30–34 year age group were 9.30% (5/43), 8.11% (4/37) and no statistical significance were found. (P < 0.05).
Table 2
Overall performance of NIPT for SCA detection
SCA type | Positive NIPT cases | Amniocentesis cases | True- positive cases | False-positive cases | PPV (%) |
45,X | 147 | 56 | 7 | 49 | 12.50 |
47,XXX | 61 | 29 | 16 | 13 | 55.17 |
47,XXY | 71 | 35 | 25 | 10 | 71.43 |
47,XYY | 35 | 13 | 10 | 3 | 76.92 |
Relationship between SCA detection rate and maternal age
The pregnant women were classified by age at due date as follows: <30, 30–34, 35–39, and ≥ 40 years, and the incidence of SCA was evaluated in each age group. There was an increasing trend with maternal age. However, the difference was statistically significant for the detection rate of SCA in different aged groups (χ2 = 17.541, P < 0.05). The incidences of 45,X and 47,XYY did not differ in pregnant women among all age groups (χ2 = 4.335, P > 0.05 for 45,X and χ2 = 1.076, P > 0.05 for 47,XYY). Meanwhile, the incidences of 47,XXX and 47,XXY were different in pregnant women among all age groups (χ2 = 11.370, P < 0.05 for 47,XXX and χ2 = 12.704, P < 0.05 for 47,XXY). (see Table 3). The incidence of 45,X in pregnant women aged 30–34 years was lower, which was no significantly different from that of the < 30 year age group. The incidence of 47,XXX in women aged ≥ 40 years was significantly different from that of the < 30 year, 30–34 year, 35–39 year age groups (P < 0.05). The incidence of 47,XXY in pregnant women aged ≥ 40 years was 0.19% (5/2568), which was significantly different from that of the < 30 year age group (P < 0.05). However, there was no statistically significant difference in the incidence of 47,XYY among different age groups. The incidence of SCA in pregnant women aged ≥ 40 years was significantly different from that of the 35–39 years age group (χ2 = 5.773, P = 0.016). Among 62 advanced-age pregnant women with positive results for SCA detected by NIPT that underwent invasive prenatal diagnosis, 30 were identified as true-positive. The results showed that the positive coincidence rate between NIPT technique and amniotic fluid karyotyping analysis was 48.39%.
Table 3
SCA screening in pregnant women of different age groups
Age (years) | Number | 45,Xa | 47,XXXb | 47,XXYc | 47,XYYd |
< 30 | 17449 | 2 (0.01) | 5 (0.03) | 4 (0.03) | 3 (0.02) |
30–34 | 11403 | 0 | 3 (0.03) | 7 (0.06) | 3 (0.03) |
35–39 | 14353 | 4 (0.03) | 4 (0.03) | 9 (0.06) | 4 (0.03) |
≥ 40 | 2568 | 1 (0.04) | 4 (0.16) | 5 (0.19) | 0 |
Total | 45773 | 7 (0.02) | 16 (0.03) | 25 (0.05) | 10 (0.02) |
a The incidence of 45,X was not significantly associated with maternal age (χ2 = 4.335, P > 0.05)
b The incidence of 47,XXX was significantly associated with maternal age (χ2 = 11.370, P < 0.05)
c The incidence of 47,XXY was significantly associated with maternal age (χ2 = 12.704, P < 0.05)
d The incidence of 47,XYY was not significantly associated with maternal age (χ2 = 1.076, P > 0.05)