J Clin Gynecol Obstet

Journal of Clinical Gynecology and Obstetrics, ISSN 1927-1271 print, 1927-128X online, Open Access

Article copyright, the authors; Journal compilation copyright, J Clin Gynecol Obstet and Elmer Press Inc

Journal website https://www.jcgo.org

Original Article

Volume 10, Number 2, June 2021, pages 46-50

Choosing the Equation for Estimated Gestational Age With Crown-Rump Length

**Table 1.** Main Characteristic of Sonographies
	N	%
CRL: crown-rump length; BPD: biparietal diameter.
CRL at first sonography (mm)
10 - 20	147	30.4
20 - 30	161	33.3
30 - 40	134	27.7
40 - 50	42	8.7
Total	484	100
CRL at second sonography (mm)
40 - 50	39	8.1
50 - 60	276	57.0
60 - 70	152	31.4
> 70	17	3.5
Total	484	100
BPD at second sonography (mm)
15 - 20	239	49.3
20 - 25	229	47.3
25 - 30	12	2.5
Not available	4	0.8
Total	484	100

Table 1. Main Characteristic of Sonographies

CRL: crown-rump length; BPD: biparietal diameter.

CRL at first sonography (mm)

10 - 20

147

30.4

20 - 30

161

33.3

30 - 40

134

27.7

40 - 50

8.7

Total

484

100

CRL at second sonography (mm)

40 - 50

8.1

50 - 60

276

57.0

60 - 70

152

31.4

> 70

3.5

Total

484

100

BPD at second sonography (mm)

15 - 20

239

49.3

20 - 25

229

47.3

25 - 30

2.5

Not available

0.8

Total

484

100

**Table 2.** The Equations
CRL: crown-rump length; GA: gestational age; sqrt: square root.
1. Robinson [2]	GA = (8.052 × sqrtCRL + 23.73)
2. Papaiouannou [4]	GA = (39.811963 + 1.155896 × CRL - 0.006429 × CRL²)
3. Constant a [5]	GA = ((19.1732 + 6.0266 × sqrtCRL + 0.0955 × CRL) + 14)
4. Constant b [5]	GA = ((18.0739 + 5.6925 × sqrtCRL + 0.1549 × CRL) + 14)
5. Constant c [5]	GA = ((17.8994 + 5.7617 × sqrtCRL + 0.1471 × CRL) + 14)
6. Constant d [5]	GA = ((19.2702 + 5.7804 × sqrtCRL + 0.1271 × CRL) + 14)
7. Papageorghiou [6]	GA = 40.9041 + (3.21585 × CRL^1/2) + (0.348956 × CRL)

Table 2. The Equations

CRL: crown-rump length; GA: gestational age; sqrt: square root.

1. Robinson [2]

GA = (8.052 × sqrtCRL + 23.73)

2. Papaiouannou [4]

GA = (39.811963 + 1.155896 × CRL - 0.006429 × CRL²)

3. Constant a [5]

GA = ((19.1732 + 6.0266 × sqrtCRL + 0.0955 × CRL) + 14)

4. Constant b [5]

GA = ((18.0739 + 5.6925 × sqrtCRL + 0.1549 × CRL) + 14)

5. Constant c [5]

GA = ((17.8994 + 5.7617 × sqrtCRL + 0.1471 × CRL) + 14)

6. Constant d [5]

GA = ((19.2702 + 5.7804 × sqrtCRL + 0.1271 × CRL) + 14)

7. Papageorghiou [6]

GA = 40.9041 + (3.21585 × CRL^1/2) + (0.348956 × CRL)

**Table 3.** Gestational Age (Days) Obtained by the Seven Equations (CRL Range: 10 - 90 mm at Intervals of 5 mm)
CRL (mm)	Gestational age (days) by seven equations	Extreme values difference (days)
*P < 0.001. R: correlation coefficient between gestational age and CRL measurement. CRL: crown-rump length.
10	49	51	53	52	52	53	55	6
15	55	56	58	56	56	58	59	4
20	60	60	62	61	61	62	62	2
25	64	65	66	64	64	65	66	2
30	68	69	69	68	68	69	69	1
35	71	72	72	71	71	72	72	1
40	75	76	75	74	74	75	75	2
45	78	79	78	77	77	78	78	2
50	81	81	81	80	80	81	81	1
55	83	84	83	83	83	84	84	1
60	86	86	86	85	85	86	87	2
65	89	88	88	88	88	88	90	2
70	91	89	90	90	90	90	92	3
75	93	90	92	93	93	93	95	5
80	96	91	95	95	95	95	98	7
85	98	92	97	98	97	97	100	8
90	100	92	99	100	100	99	103	11
R	0.990*	0.966*	0.993*	0.994*	0.995*	0.995*	0.999*

Table 3. Gestational Age (Days) Obtained by the Seven Equations (CRL Range: 10 - 90 mm at Intervals of 5 mm)

CRL (mm)

Gestational age (days) by seven equations

Extreme values difference (days)

1. Robinson [2]

2. Papaiounnou [4]

3. Constant a [5]

4. Constant b [5]

5. Constant c [5]

6. Constant d [5]

7. Papageorghiou [6]

*P < 0.001. R: correlation coefficient between gestational age and CRL measurement. CRL: crown-rump length.

100

103

0.990*

0.966*

0.993*

0.994*

0.995*

0.999*

**Table 4.** Initial CRL and CRL Growth
First CRL (mm)	N	Growth rate (mm/day), mean (SD)	95% CI
R² = 0.333 (P < 0.001). CI: confidence interval; CRL: crown-rump length; SD: standard deviation.
10 - 15	60	1.46 (0.22)	1.40 - 1.52
15 - 20	87	1.53 (0.24)	1.48 - 1.58
20 - 25	71	1.64 (0.24)	1.58 - 1.70
25 - 30	90	1.72 (0.28)	1.66 - 1.78
30 - 35	73	1.80 (0.38)	1.71 - 1.89
35 - 40	61	1.72 (0.37)	1.62 - 1.81
> 40	42	1.86 (0.73)	1.63 - 2.01
Total	484

Table 4. Initial CRL and CRL Growth

First CRL (mm)

Growth rate (mm/day), mean (SD)

95% CI

R² = 0.333 (P < 0.001). CI: confidence interval; CRL: crown-rump length; SD: standard deviation.

10 - 15

1.46 (0.22)

1.40 - 1.52

15 - 20

1.53 (0.24)

1.48 - 1.58

20 - 25

1.64 (0.24)

1.58 - 1.70

25 - 30

1.72 (0.28)

1.66 - 1.78

30 - 35

1.80 (0.38)

1.71 - 1.89

35 - 40

1.72 (0.37)

1.62 - 1.81

> 40

1.86 (0.73)

1.63 - 2.01

Total

484

**Table 5.** Sonography Interval and CRL Growth
Interval (days)	N	Growth rate (mm/day), mean (SD)	95% CI
R² = 0.363 (P < 0.001). CI: confidence interval; CRL: crown-rump length; SD: standard deviation.
7 - 14	121	1.82 (0.52)	1.73 - 1.91
14 - 21	142	1.73 (0.31)	1.68 - 1.78
21 - 28	125	1.60 (0.24)	1.56 - 1.64
28 - 35	84	1.47 (0.18)	1.43 - 1.51
≥ 35	12	1.31 (0.17)	1.20 - 1.42
Total	484

Table 5. Sonography Interval and CRL Growth

Interval (days)

Growth rate (mm/day), mean (SD)

95% CI

R² = 0.363 (P < 0.001). CI: confidence interval; CRL: crown-rump length; SD: standard deviation.

7 - 14

121

1.82 (0.52)

1.73 - 1.91

14 - 21

142

1.73 (0.31)

1.68 - 1.78

21 - 28

125

1.60 (0.24)

1.56 - 1.64

28 - 35

1.47 (0.18)

1.43 - 1.51

≥ 35

1.31 (0.17)

1.20 - 1.42

Total

484

**Table 6.** Maternal BMI and CRL Growth
BMI (kg/m²)	N	Growth rate (mm/day), mean (SD)	95% CI
R² = 0.009 (P > 0.05). CI: confidence interval; BMI: body mass index; CRL: crown-rump length; SD: standard deviation.
20 - 25	237	1.63 (0.33)	1.59 - 1.67
25 - 30	130	1.70 (0.49)	1.61 - 1.67
30 - 35	43	1.69 (0.35)	1.58 - 1.79
≥ 35	21	1.66 (0.26)	1.54 - 1.77
Not available	53
Total	484

Table 6. Maternal BMI and CRL Growth

BMI (kg/m²)

Growth rate (mm/day), mean (SD)

95% CI

R² = 0.009 (P > 0.05). CI: confidence interval; BMI: body mass index; CRL: crown-rump length; SD: standard deviation.

20 - 25

237

1.63 (0.33)

1.59 - 1.67

25 - 30

130

1.70 (0.49)

1.61 - 1.67

30 - 35

1.69 (0.35)

1.58 - 1.79

≥ 35

1.66 (0.26)

1.54 - 1.77

Not available

Total

484

**Table 7.** The Difference of GA (Days) Between First and Second Sonography (Ʃ (%) of Summaries of Previous Results of the Row)
(days of difference)	0	1	-1	Ʃ (%)	2	-2	Ʃ (%)	3	-3	Ʃ (%)	4	-4	5	-5	Ʃ (%)	≥ 6	≤ -6	R²	Chi-square
R²: regression on the interval of the two CRL measurements and the differences in gestational age, P < 0.01. Chi-square of GA distribution: equation 6 reference, P < 0.01. GA: gestational age; CRL: crown-rump length.
1. Robinson [2]	16	7	27	50 (10.3)	1	51	102 (21.1)	2	67	171 (35.3)	1	68	0	59	299 (61.8)	0	185	0.000	307*
2. Papaiounnou [4]	14	6	34	54 (11.2)	3	50	107 (22.1)	2	69	178 (36.8)	1	66	0	56	301 (62.2)	0	183	0.087*	295*
3. Constant a [5]	75	52	76	203 (41.9)	26	68	297 (61.4)	22	48	367 (75.8)	11	34	8	27	447 (91.7)	5	32	0.107*	16*
4. Constant b [5]	80	66	60	206 (42.6)	45	50	301 (62.2)	37	37	375 (77.5)	18	25	13	16	449 (92.3)	17	20	0.052*	14*
5. Constant c [5]	66	70	51	187 (38.6)	72	33	292 (60.3)	55	25	372 (76.8)	30	16	19	6	443 (91.5)	33	8	0.227*	20*
6. Constant d [5]	81	92	57	230 (47.5)	55	57	342 (70.7)	41	25	408 (84.3)	20	19	14	9	470 (97.1)	5	9	0.000	Reference
7. Papageorghiou [6]	71	62	56	189 (39.0)	47	58	294 (60.7)	31	27	352 (72.7)	20	33	13	18	436 (90.0)	19	29	0.121*	26*

Table 7. The Difference of GA (Days) Between First and Second Sonography (Ʃ (%) of Summaries of Previous Results of the Row)

(days of difference)

-1

Ʃ (%)

-2

Ʃ (%)

-3

Ʃ (%)

-4

-5

Ʃ (%)

≥ 6

≤ -6

R²

Chi-square

R²: regression on the interval of the two CRL measurements and the differences in gestational age, *P < 0.01. Chi-square of GA distribution: equation 6 reference, *P < 0.01. GA: gestational age; CRL: crown-rump length.

1. Robinson [2]

50 (10.3)

102 (21.1)

171 (35.3)

299 (61.8)

185

0.000

307*

2. Papaiounnou [4]

54 (11.2)

107 (22.1)

178 (36.8)

301 (62.2)

183

0.087*

295*

3. Constant a [5]

203 (41.9)

297 (61.4)

367 (75.8)

447 (91.7)

0.107*

16*

4. Constant b [5]

206 (42.6)

301 (62.2)

375 (77.5)

449 (92.3)

0.052*

14*

5. Constant c [5]

187 (38.6)

292 (60.3)

372 (76.8)

443 (91.5)

0.227*

20*

6. Constant d [5]

230 (47.5)

342 (70.7)

408 (84.3)

470 (97.1)

0.000

Reference

7. Papageorghiou [6]

189 (39.0)

294 (60.7)

352 (72.7)

436 (90.0)

0.121*

26*