. 2020 Oct 19;128(2):195–206. doi: 10.1111/1471-0528.16519

Table 2.

Discriminative ability of shortest endocervical length (distance A‐B) measured at 21 + 0 to 23 + 6 gestational weeks (C×2, n = 6288) with regard to predicting spontaneous preterm birth

sPTB	No. sPTB (%)	AUC [95% CI]	Cervical length
<28 GW	3 (0.05)	0.96 [0.92–1.00]	1/3 (33.3%) [0.8–90.6]	6272/6285 (99.8%) [99.7–99.9]	13; 6288	1/3 (33.3%) [0.8–90.6]	6215/6285 (98.9%) [98.6–99.1]	70; 6288	1/3 (33.3%) [0.8–90.6]	6012/6285 (95.7%) [95.1–96.2]	273; 6288	3/3 (100%) [29.2–100]	5778/6285 (91.9%) [91.2–92.6]	169; 2096	27 (n = 510; 8.1%)
<29 GW	5 (0.08)	0.98 [0.95–1.00]	3/5 (60.0%) [14.7–94.7]	6272/6283 (99.8%) [99.7–99.9]	4; 2096	3/5 (60.0%) [14.7–94.7]	6215/6283 (98.9%) [98.6–99.2]	23; 2096	3/5 (60.0%) [14.7–94.7]	6012/6283 (95.7%) [95.2–96.2]	90; 2096	5/5 (100%) [47.8–100]	5778/6283 (92.0%) [91.3–92.6]	101; 1258	27 (n = 510; 8.1%)
<30 GW	10 (0.16)	0.86 [0.69–1.00]	5/10 (50.0%) [18.7–81.3]	6269/6278 (99.9%) [99.7–99.9]	2; 1257	6/10 (60.0%) [26.2–87.8]	6213/6278 (99.0%) [98.7–99.2]	11; 1048	6/10 (60.0%) [26.3–87.8]	6010/6278 (95.7%) [95.2–96.2]	45; 1048	8/10 (80.0%) [44.4–97.5]	5776/6278 (92.0%) [91.3–92.7]	63; 786	27 (n = 510; 8.1%)
<31 GW	15 (0.24)	0.85 [0.72–0.99]	6/15 (40.0%) [16.3–67.7]	6265/6273 (99.9%) [99.8–99.9]	1; 1048	8/15 (53.3%) [26.6–78.7]	6210/6273 (99.0%) [98.7–99.2]	8; 786	8/15 (53.3%) [26.6–78.7]	6007/6273 (95.8%) [95.2–96.2]	33; 786	11/15 (73.3%) [44.9–92.2]	5774/6273 (92.0%) [91.4–92.7]	45; 572	27 (n = 510; 8.1%)
<32 GW	18 (0.29)	0.81 [0.68–0.93]	6/18 (33.3%) [13.3–59.0]	6262/6270 (99.9%) [99.8–99.9]	1; 1048	8/18 (44.4%) [21.5–69.2]	6207/6270 (99.0%) [98.7–99.2]	8; 786	8/18 (44.4%) [21.5–69.2]	6004/6270 (95.8%) [95.2–96.2]	33; 786	11/18 (61.1%) [35.8–82.7]	5771/6270 (92.0%) [91.3–92.7]	45; 572	27 (n = 510; 8.1%)
<33 GW	26 (0.41)	0.76 [0.65–0.87]	6/26 (23.1%) [9.0–43.7]	6254/6262 (99.9%) [99.8–99.9]	1; 1048	9/26 (34.6%) [17.2–55.7]	6200/6262 (99.0%) [98.7–99.2]	7; 699	10/26 (38.5%) [20.3–59.4]	5998/6262 (95.8%) [95.3–96.3]	26; 629	14/26 (53.8%) [33.4–73.4]	5766/6262 (92.1%) [91.4–92.7]	35; 449	27 (n = 510; 8.1%)
<34 GW	41 (0.65)	0.71 [0.63–0.80]	6/41 (14.6%) [5.6–29.2]	6239/6247 (99.9%) [99.8–99.9]	1; 1048	10/41 (24.4%) [12.4–40.3]	6186/6247 (99.0%) [98.8–99.3]	6; 629	12/41 (29.3%) [16.1–45.5]	5985/6247 (95.8%) [95.3–96.3]	22; 524	16/41 (39.0%) [24.2–55.5]	5753/6247 (92.1%) [91.4–92.8]	31; 393	27 (n = 510; 8.1%)
<35 GW	69 (1.10)	0.71 [0.65–0.77]	7/69 (10.1%) [4.2–19.8]	6212/6219 (99.9%) [99.8–100.0]	1; 898	13/69 (18.8%) [10.4–30.1]	6161/6219 (99.1%) [98.8–99.3]	5; 484	17/69 (24.6%) [15.1–36.5]	5962/6219 (95.9%) [95.3–96.4]	15; 370	53/69 (76.8%) [65.1–86.1]	3346/6219 (53.8%) [52.6–55.1]	54; 119	35 (n = 2926; 46.5%)
<36 GW	114 (1.81)	0.67 [0.61–0.72]	7/114 (6.1%) [2.5–12.2]	6167/6174 (99.9%) [99.8–100.0]	1; 898	15/114 (13.2%) [7.6–20.8]	6118/6174 (99.1%) [98.8–99.3]	4; 419	23/114 (20.2%) [13.2–28.7]	5923/6174 (95.9%) [95.4–96.4]	11; 273	81/114 (71.1%) [61.8–79.2]	3329/6174 (53.9%) [52.7–55.2]	35; 78	35 (n = 2926; 46.5%)
<37 GW	225 (3.58)	0.63 [0.59–0.67]	7/225 (3.1%) [1.3–6.3]	6056/6063 (99.9%) [99.8–100.0]	1; 898	18/225 (8.0%) [4.8–12.4]	6010/6063 (99.1%) [98.9–99.3]	3; 349	34/225 (15.1%) [10.7–20.5]	5823/6063 (96.0%) [95.5–96.5]	7; 185	144/225 (64.0%) [57.4–70.3]	3281/6063 (54.1%) [52.9–55.4]	19; 44	35 (n = 2926; 46.5%)

sPTB

No. sPTB (%)

AUC

[95% CI]

Cervical length

0–15 mm (n = 14; 0.22%)

0–20 mm (n = 71; 1.1%)

0–25 mm (n = 274; 4.4%)

Best cut‐off^*

Sensitivity

[95% CI]

Specificity

[95% CI]

FP/TP;

NNS

Sensitivity

[95% CI]

Specificity

[95% CI]

FP/TP;

NNS

Sensitivity

[95% CI]

Specificity

[95% CI]

FP/TP;

NNS

Sensitivity

[95% CI]

Specificity

[95% CI]

FP/TP;

NNS

<28 GW

(0.05)

0.96

[0.92–1.00]

1/3

(33.3%)

[0.8–90.6]

6272/6285

(99.8%)

[99.7–99.9]

13;

6288

1/3

(33.3%)

[0.8–90.6]

6215/6285 (98.9%)

[98.6–99.1]

70;

6288

1/3

(33.3%)

[0.8–90.6]

6012/6285 (95.7%)

[95.1–96.2]

273;

6288

3/3

(100%)

[29.2–100]

5778/6285 (91.9%)

[91.2–92.6]

169;

2096

(n = 510; 8.1%)

<29 GW

(0.08)

0.98

[0.95–1.00]

3/5

(60.0%)

[14.7–94.7]

6272/6283

(99.8%)

[99.7–99.9]

2096

3/5

(60.0%)

[14.7–94.7]

6215/6283 (98.9%)

[98.6–99.2]

23;

2096

3/5

(60.0%)

[14.7–94.7]

6012/6283 (95.7%)

[95.2–96.2]

90;

2096

5/5

(100%)

[47.8–100]

5778/6283 (92.0%)

[91.3–92.6]

101;

1258

(n = 510; 8.1%)

<30 GW

(0.16)

0.86

[0.69–1.00]

5/10

(50.0%)

[18.7–81.3]

6269/6278 (99.9%)

[99.7–99.9]

1257

6/10

(60.0%)

[26.2–87.8]

6213/6278 (99.0%)

[98.7–99.2]

11;

1048

6/10

(60.0%)

[26.3–87.8]

6010/6278 (95.7%)

[95.2–96.2]

45;

1048

8/10

(80.0%)

[44.4–97.5]

5776/6278 (92.0%)

[91.3–92.7]

63;

786

(n = 510; 8.1%)

<31 GW

(0.24)

0.85

[0.72–0.99]

6/15

(40.0%)

[16.3–67.7]

6265/6273 (99.9%)

[99.8–99.9]

1048

8/15

(53.3%)

[26.6–78.7]

6210/6273 (99.0%)

[98.7–99.2]

786

8/15

(53.3%)

[26.6–78.7]

6007/6273 (95.8%)

[95.2–96.2]

33;

786

11/15

(73.3%)

[44.9–92.2]

5774/6273 (92.0%)

[91.4–92.7]

45;

572

(n = 510; 8.1%)

<32 GW

(0.29)

0.81

[0.68–0.93]

6/18

(33.3%)

[13.3–59.0]

6262/6270 (99.9%)

[99.8–99.9]

1048

8/18

(44.4%)

[21.5–69.2]

6207/6270 (99.0%)

[98.7–99.2]

786

8/18

(44.4%)

[21.5–69.2]

6004/6270 (95.8%)

[95.2–96.2]

33;

786

11/18

(61.1%)

[35.8–82.7]

5771/6270 (92.0%)

[91.3–92.7]

45;

572

(n = 510; 8.1%)

<33 GW

(0.41)

0.76

[0.65–0.87]

6/26

(23.1%)

[9.0–43.7]

6254/6262 (99.9%)

[99.8–99.9]

1048

9/26

(34.6%)

[17.2–55.7]

6200/6262 (99.0%)

[98.7–99.2]

699

10/26

(38.5%)

[20.3–59.4]

5998/6262 (95.8%)

[95.3–96.3]

26;

629

14/26

(53.8%)

[33.4–73.4]

5766/6262 (92.1%)

[91.4–92.7]

35;

449

(n = 510; 8.1%)

<34 GW

(0.65)

0.71

[0.63–0.80]

6/41

(14.6%)

[5.6–29.2]

6239/6247 (99.9%)

[99.8–99.9]

1048

10/41

(24.4%)

[12.4–40.3]

6186/6247 (99.0%)

[98.8–99.3]

629

12/41

(29.3%)

[16.1–45.5]

5985/6247 (95.8%)

[95.3–96.3]

22;

524

16/41

(39.0%)

[24.2–55.5]

5753/6247 (92.1%)

[91.4–92.8]

31;

393

(n = 510; 8.1%)

<35 GW

(1.10)

0.71

[0.65–0.77]

7/69

(10.1%)

[4.2–19.8]

6212/6219 (99.9%)

[99.8–100.0]

898

13/69

(18.8%)

[10.4–30.1]

6161/6219 (99.1%)

[98.8–99.3]

484

17/69

(24.6%)

[15.1–36.5]

5962/6219 (95.9%)

[95.3–96.4]

15;

370

53/69

(76.8%)

[65.1–86.1]

3346/6219 (53.8%)

[52.6–55.1]

54;

119

(n = 2926; 46.5%)

<36 GW

114 (1.81)

0.67

[0.61–0.72]

7/114

(6.1%)

[2.5–12.2]

6167/6174 (99.9%)

[99.8–100.0]

898

15/114

(13.2%)

[7.6–20.8]

6118/6174 (99.1%)

[98.8–99.3]

419

23/114

(20.2%)

[13.2–28.7]

5923/6174 (95.9%)

[95.4–96.4]

11;

273

81/114

(71.1%)

[61.8–79.2]

3329/6174 (53.9%)

[52.7–55.2]

35;

(n = 2926; 46.5%)

<37 GW

225 (3.58)

0.63

[0.59–0.67]

7/225

(3.1%)

[1.3–6.3]

6056/6063 (99.9%)

[99.8–100.0]

898

18/225

(8.0%)

[4.8–12.4]

6010/6063 (99.1%)

[98.9–99.3]

349

34/225

(15.1%)

[10.7–20.5]

5823/6063 (96.0%)

[95.5–96.5]

185

144/225

(64.0%)

[57.4–70.3]

3281/6063 (54.1%)

[52.9–55.4]

19;

(n = 2926; 46.5%)

Positive and negative predictive values and positive and negative likelihood ratios are shown in Table S9.

GW, gestational weeks; sPTB, spontaneous preterm birth; AUC, area under receiver operating characteristic curve; CI, confidence interval; FP, false positive; TP, true positive; NNS, number needed to screen, i.e. number of women needed to screen to detect one true positive test result.

Best cut‐off is the cut‐off associated with the largest number of correctly classified cases, calculated using Youden’s index. ²¹