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110
Chapter 3 Biometry of the Fetal Brain
Table 3–4. ASSESSMENT OF GESTATIONAL AGE FROM THE BIPARIETAL DIAMETER (CONTINUED)
Gestational Age (weeks + days)
Biparietal Diameter (mm)
42 14 + 6 18 + 0 21 + 0
43 15 + 1 18 + 2 21 + 2
44 15 + 3 18 + 4 21 + 4
45 15 + 6 18 + 6 21 + 6
46 16 + 1 19 + 1 22 + 1
47 16 + 3 19 + 3 22 + 4
48 16 + 5 19 + 5 22 + 6
49 17 + 0 20 + 1 23 + 1
50 17 + 3 20 + 3 23 + 3
51 17 + 5 20 + 5 23 + 6
52 18 + 0 21 + 0 24 + 1
53 18 + 2 21 + 3 24 + 3
54 18 + 5 21 + 5 24 + 5
55 19 + 0 22 + 0 25 + 1
56 19 + 2 22 + 3 25 + 3
57 19 + 5 22 + 5 25 + 6
58 20 + 0 23 + 1 26 + 1
59 20 + 3 23 + 3 26 + 3
60 20 + 5 23 + 6 26 + 6
61 21 + 1 24 + 1 27 + 1
62 21 + 3 24 + 4 27 + 4
63 21 + 6 24 + 6 27 + 6
64 22 + 1 25 + 2 28 + 2
65 22 + 4 25 + 4 28 + 5
66 22 + 6 26 + 0 29 + 0
67 23 + 2 26 + 2 29 + 3
68 23 + 5 26 + 5 29 + 5
69 24 + 0 27 + 1 30 + 1
70 24 + 3 27 + 3 30 + 4
71 24 + 6 27 + 6 30 + 6
72 25 + 1 28 + 2 31 + 2
73 25 + 4 28 + 5 31 + 5
5th Percentile 50th Percentile 95th Percentile
(continued)
Chapter 3 Biometry of the Fetal Brain
Table 3–4. ASSESSMENT OF GESTATIONAL AGE FROM THE BIPARIETAL DIAMETER (CONTINUED)
Gestational Age (weeks + days)
111
Biparietal Diameter (mm)
74 26 + 0 29 + 0 32 + 1
75 26 + 3 29 + 3 32 + 4
76 26 + 6 29 + 6 32 + 6
77 27 + 1 30 + 2 33 + 2
78 27 + 4 30 + 5 33 + 5
79 28 + 0 31 + 1 34 + 1
80 28 + 3 31 + 3 34 + 4
81 28 + 6 31 + 6 35 + 0
82 29 + 2 32 + 2 35 + 3
83 29 + 5 32 + 5 35 + 6
84 30 + 1 33 + 1 36 + 2
85 30 + 4 33 + 4 36 + 5
86 31 + 0 34 + 0 37 + 1
87 31 + 3 34 + 3 37 + 4
88 31 + 6 35 + 0 38 + 0
89 32 + 2 35 + 3 38 + 3
90 32 + 5 35 + 6 38 + 6
91 33 + 2 36 + 2 39 + 2
92 33 + 5 36 + 5 39 + 6
93 34 + 1 37 + 1 40 + 2
94 34 + 4 37 + 5 40 + 5
95 35 + 0 38 + 1 41 + 1
96 35 + 4 38 + 4 41 + 4
97 36 + 0 39 + 0 42 + 1
98 36 + 3 39 + 4 42 + 4
99 37 + 0 40 + 0 43 + 0
5th Percentile 50th Percentile 95th Percentile
From Jeanty P. Fetal biometry. In Fleischer AC, Romero R, et al. The Principles and Practice of Ultrasonography in Obstetrics and Gynecology . 4th ed.
East Norwalk, CT: Appleton & Lange; 1991:100, with permission.
the fetal head shape, (eg, oligohydramnios and breech
presentation
be used.
Hadlock and coworkers
13 , 14
), other parameters, such as the HC, should
12
suggested that the CI is
constant throughout gestation, with a mean value of
78.3 and a standard deviation (SD) of 4.4. A CI > 1 SD
from the mean (< 74 or > 83) was found to be associated with a significant change in the BPD measurement
expected for any given age. Using the CI, certain variations in the shape of the fetal skull, such as dolichocephaly (CI < 74) and brachycephaly (CI > 84), have been
described.
12
112
Chapter 3 Biometry of the Fetal Brain
Gray and collaborators
10
proposed that the CI varies
with advancing age ( Table 3–5 ). These authors also sug-
gested that the normal CI range is within 1 SD of the mean,
with a sensitivity of 84% and a false-positive rate of 35% for
detection of a misleading BPD value.
The head/abdominal circumference ratio was used to
determine growth restriction in fetuses.
15
Table 3–5. CEPHALIC INDEX: MEAN AND
NORMAL RANGE
Mean
Week
14 81.5 77.8 85.3
15 81.0 77.3 84.8
16 80.5 76.8 84.3
17 80.1 76.4 83.9
18 79.7 76.0 83.5
19 79.4 75.7 83.2
20 79.1 75.4 82.9
21 78.8 75.1 82.6
22 78.6 74.9 82.4
23 78.4 74.7 82.2
24 78.3 74.6 82.0
25 78.1 74.4 81.9
26 78.0 74.3 81.8
27 78.0 74.3 81.8
28 78.0 74.3 81.8
29 78.0 74.3 81.8
30 78.1 74.4 81.9
31 78.2 74.5 82.0
32 78.3 74.6 82.1
33 78.5 74.8 82.3
34 78.7 75.0 82.5
35 78.9 75.2 82.7
36 79.2 75.5 83.0
37 79.5 75.8 83.3
38 79.9 76.2 83.7
39 80.3 76.6 84.1
40 80.7 77.0 84.5
From Gray and colleagues, 1989,
Cephalic Index −1 SD +1 SD
10
with permission.
HEAD CIRCUMFERENCE
Definition
The HC represents the outer perimeter of the fetal calvarium measured at the level of the BPD.
How to Measure It
The correct anatomical plane that should be used to measure the HC corresponds to the axial plane described by
Campbell and Thoms,
on BPD. Ideally, the formula for the circumference of an
ellipse should be used.
HC = √(transverse diameter)
Both transverse and longitudinal diameters should be
outer-to-outer distances (as for the CI). Adequate calculation of the HC can also be made using the formula
The HC can also be measured along the outer perimeter of the calvarium, using a map measurer or electronic
digitizer, as originally described by Hadlock’s group.
The calculation of a circumference from two diameters
is equivalent to the electronically digitized perimeter
measurement, although the probability of technical errors
between these techniques exists.
Comments
The HC was originally described as a useful index to estimate fetal age in cases in which variations in head shape
(eg, dolichocephaly or brachycephaly) adversely affected
the accuracy of the BPD.
strated that the HC is a better predictor of fetal age than
the BPD.
pendent, and thus is less prone to be affected by molding
of the fetal head ( Tables 3–6 and 3–7 ).
ability for estimation of age via the HC progressively
increases with advancing menstrual age, ranging from
±1.19 at the 12- to 18-week interval to ±2.70 at the 36- to
42-week interval ( Table 3–8 ).
to estimate fetal weight,
as well as intrauterine growth restriction,
diagnosis of microcephaly ( Table 3–9 ). Microcephaly
is a clinical syndrome characterized by an abnormally
small head. Most authors agree that the diagnosis of
microcephaly should be suspected when the HC is 3
SD below the mean for a given gestational age.
Nevertheless, the antenatal accuracy for the diagnosis of
microcephaly using this parameter has been reported to
be as low as 56.2%.
other measurements, such as the frontal lobe distance
and the thalamic frontal lobe distance, have been proposed.
such as a cone-shaped head, a large face, large ears, and
a sloping forehead (“birdhead”),
20 – 22
This is because the HC is more shape inde-
As with other parameters, such as the BPD, the vari-
The HC has also been used in equations developed
29
Other typical features of microcephalic fetuses,
6
previously delineated in the section
16
2
+ (longitudinal diameter)
2
17
/2 × п
[D1 + D2] × 1.57
19
Several authors have demon-
9
23
to monitor normal fetal growth
28
To overcome this low performance,
29
24 , 25
and for the
as well as associated
17,18
26 – 28
Chapter 3 Biometry of the Fetal Brain
Table 3–6. PREDICTED HEAD CIRCUMFERENCE AT SPECIFIC MENSTRUAL AGES
113
Menstrual Age
(weeks)
12.0 6.8 26.5 25.1
12.5 7.5 27.0 25.6
13.0 8.2 27.5 26.1
13.5 8.9 28.0 26.6
14.0 9.7 28.5 27.1
14.5 10.4 29.0 27.5
15.0 11.0 29.5 28.0
15.5 11.7 30.0 28.4
16.0 12.4 30.5 28.8
16.5 13.1 31.0 29.3
17.0 13.8 31.5 29.7
17.5 14.4 32.0 30.1
18.0 15.1 32.5 30.4
18.5 15.8 33.0 30.8
19.0 16.4 33.5 31.2
19.5 17.0 34.0 31.5
20.0 17.7 34.5 31.8
20.5 18.3 35.0 32.2
21.0 18.9 35.5 32.5
21.5 19.5 36.0 32.8
22.0 20.1 36.5 33.0
22.5 20.7 37.0 33.3
23.0 21.3 37.5 33.5
23.5 21.9 38.0 33.8
24.0 22.4 38.5 34.0
24.5 23.0 39.0 34.2
25.0 23.5 39.5 34.4
25.5 24.1 40.0 34.6
26.0 24.6
After Hadlock and colleagues, 1984,
Head
Circumference (cm)
9
with permission.
Menstrual Age
(weeks)
Head
Circumference (cm)
114
Chapter 3 Biometry of the Fetal Brain
Table 3–7. ASSESSMENT OF GESTATIONAL AGE FROM THE HEAD CIRCUMFERENCE
Gestational Age (weeks + days)
Head Perimeter (mm)
80 10 + 5 12 + 4 14 + 2
84 11 + 0 12 + 5 14 + 4
88 11 + 2 13 + 0 14 + 6
92 11 + 4 13 + 2 15 + 0
96 11 + 6 13 + 4 15 + 2
100 12 + 1 13 + 6 15 + 4
104 12 + 3 14 + 1 15 + 6
108 12 + 5 14 + 3 16 + 1
112 13 + 0 14 + 5 16 + 3
116 13 + 2 15 + 0 16 + 5
120 13 + 4 15 + 2 17 + 0
124 13 + 6 15 + 4 17 + 2
128 14 + 1 15 + 6 17 + 5
132 14 + 3 16 + 1 18 + 0
136 14 + 5 16 + 4 18 + 2
140 15 + 0 16 + 6 18 + 4
144 15 + 3 17 + 1 18 + 6
148 15 + 5 17 + 3 19 + 2
152 16 + 0 17 + 6 19 + 4
156 16 + 3 18 + 1 19 + 6
160 16 + 5 18 + 3 20 + 1
164 17 + 0 18 + 6 20 + 4
168 17 + 3 19 + 1 20 + 6
172 17 + 5 19 + 3 21 + 2
176 18 + 0 19 + 6 21 + 4
180 18 + 3 20 + 1 21 + 6
184 18 + 5 20 + 4 22 + 2
188 19 + 1 20 + 6 22 + 4
192 19 + 3 21 + 2 23 + 0
196 19 + 6 21 + 4 23 + 3
200 20 + 2 22 + 0 23 + 5
204 20 + 4 22 + 2 24 + 1
5th Percentile 50th Percentile 95th Percentile
(continued)
Chapter 3 Biometry of the Fetal Brain
Table 3–7. ASSESSMENT OF GESTATIONAL AGE FROM THE HEAD CIRCUMFERENCE (CONTINUED)
Gestational Age (weeks + days)
115
Head Perimeter (mm)
208 21 + 0 22 + 5 24 + 3
212 21 + 2 23 + 1 24 + 6
216 21 + 5 23 + 3 25 + 2
220 22 + 1 23 + 6 25 + 4
224 22 + 4 24 + 2 26 + 0
228 22 + 6 24 + 5 26 + 3
232 23 + 2 25 + 0 26 + 6
236 23 + 5 25 + 3 27 + 2
240 24 + 1 25 + 6 27 + 4
244 24 + 4 26 + 2 28 + 0
248 25 + 0 26 + 5 28 + 3
252 25 + 3 27 + 1 28 + 6
256 25 + 6 27 + 4 29 + 2
260 26 + 1 28 + 0 29 + 5
264 26 + 4 28 + 3 30 + 1
268 27 + 1 28 + 6 30 + 4
272 27 + 4 29 + 2 31 + 0
276 28 + 0 29 + 5 31 + 3
280 28 + 3 30 + 1 31 + 6
284 28 + 6 30 + 4 32 + 2
288 29 + 2 31 + 0 32 + 6
292 29 + 5 31 + 4 33 + 2
296 30 + 1 32 + 0 33 + 5
300 30 + 5 32 + 3 34 + 1
304 31 + 1 32 + 6 34 + 5
308 31 + 4 33 + 3 35 + 1
312 32 + 1 33 + 6 35 + 4
316 32 + 4 34 + 2 36 + 0
320 33 + 0 34 + 6 36 + 4
324 33 + 4 35 + 2 37 + 0
328 34 + 0 35 + 5 37 + 4
332 34 + 4 36 + 2 38 + 0
5th Percentile 50th Percentile 95th Percentile
(continued)
116
Chapter 3 Biometry of the Fetal Brain
Table 3–7. ASSESSMENT OF GESTATIONAL AGE FROM THE HEAD CIRCUMFERENCE (CONTINUED)
Gestational Age (weeks + days)
Head Perimeter (mm)
336 35 + 0 36 + 5 38 + 4
340 35 + 3 37 + 2 39 + 0
344 36 + 0 37 + 5 39 + 4
348 36 + 4 38 + 2 40 + 0
352 37 + 0 38 + 5 40 + 4
356 37 + 4 39 + 2 41 + 0
360 38 + 0 39 + 6 41 + 4
364 38 + 4 40 + 2 42 + 1
From Jeanty P. Fetal biometry. In Fleischer AC, Romero R, Manning FA, Jeanty P, James AE. The Principles and Practice of Ultrasonography in Obstetrics
and Gynecology . 4th ed. East Norwalk, CT: Appleton & Lange; 1991:102, with permission.
anomalies such as ventricular enlargement, porencephaly,
and cephaloceles,
28
should be carefully searched. Some
investigators have postulated that a reduction in blood
supply to the underdeveloped cerebral hemispheres in
fetuses with microcephaly could be detected with color
Doppler and power Doppler imaging.
As the nomograms for HC require knowledge of
the accurate fetal age, and this information is not always
available, the use of ratios such as the HC-to-femur length
ratios has the advantage of reducing dependence on reliable age evaluation ( Table 3–10 ).
limb growth is not affected in fetuses with microcephaly,
which might not always be the case.
5th Percentile 50th Percentile 95th Percentile
ORBITAL DIAMETERS: INNER ORBITAL
DIAMETER, OUTER ORBITAL DIAMETER,
AND OCULAR DIAMETER
30
28
This ratio assumes that
Definition
The inner orbital, or interorbital, diameter (IOD) is defined
as the distance between the medial border of one orbit and
the medial border of the opposite orbit. The outer orbital,
or biorbital, diameter (OOD) is defined as the distance
between the lateral border of one orbit and the lateral
border of the opposite orbit.
sponds to the distance between the medial border and the
31
The ocular diameter corre-
lateral border of a single orbit.
Table 3–8. VARIABILITY IN PREDICTING MENSTRUAL AGE USING THE BIPARIETAL DIAMETER
AND THE HEAD CIRCUMFERENCE
Subgroup Variability (± 2 SD) in Weeks
Fetal
Parameters
Biparietal
diameter
Head
circumference
Modified from Hadlock and colleagues, 1984,
12–18 Weeks 18–24 Weeks 24–30 Weeks 30–36 Weeks 36–42 Weeks
±1.19 ±1.73 ±2.18 ±3.08 ±3.20
±1.19 ±1.48 ±2.06 ±2.98 ±2.70
9
with permission.
Chapter 3 Biometry of the Fetal Brain
Table 3–9. MEANS AND STANDARD DEVIATIONS OF THE HEAD CIRCUMFERENCE
AS A FUNCTION OF GESTATIONAL AGE
Head Circumference (mm): SD Below Mean
Week Mean −1 −2 −3 −4 −5
20 175 160 145 131 116 101
21 187 172 157 143 128 113
22 198 184 169 154 140 125
23 210 195 180 166 151 136
24 221 206 191 177 162 147
25 232 217 202 188 173 158
26 242 227 213 198 183 169
27 252 238 223 208 194 179
28 262 247 233 218 203 189
29 271 257 242 227 213 198
30 281 266 251 236 222 207
31 289 274 260 245 230 216
32 297 283 268 253 239 224
33 305 290 276 261 246 232
34 312 297 283 268 253 239
35 319 304 289 275 260 245
36 325 310 295 281 266 251
37 330 316 301 286 272 257
38 335 320 306 291 276 262
39 339 325 310 295 281 266
40 343 328 314 299 284 270
41 346 331 316 302 287 272
42 348 333 319 304 289 275
117
SD, standard deviation.
From Chervenak and colleagues, 1984,
28
with permission.
How to Measure It ( Figure 3–3 )
To measure the orbital diameters, an axial plane slightly
caudad to the BPD is commonly used. The criteria used
for this section are (1) a symmetrical section, (2) both eyes
imaged and of equal diameter, and (3) the largest possible
diameter of the eyes.
can also be accomplished using a coronal plane, ~2 cm
posterior to the glabella-alveolar line.
32
Measurements of orbital diameters
31
Comments
The study of the orbital diameters should help in the diagnosis of hypotelorism, hypertelorism, and microphthalmos. Trout and colleagues
hypotelorism, both the IOD and the OOD clearly fall
below 2 SD of the mean. In cases of hypertelorism, the
IOD fell above the 95th percentile, whereas the OOD
measurement fell within normal limits but near the 95th
33
have found that in cases of
118
Chapter 3 Biometry of the Fetal Brain
Table 3–10. MEANS AND STANDARD DEVIATIONS OF THE FEMUR LENGTH: HEAD CIRCUMFERENCE
RATIOS AS A FUNCTION OF GESTATIONAL AGE
SD Below Mean
Week Mean −5 −4 −3 −2 −1
20 0.180 0.107 0.122 0.137 0.152 0.167
21 0.190 0.111 0.126 0.141 0.156 0.171
22 0.190 0.115 0.130 0.145 0.160 0.175
23 0.190 0.118 0.133 0.148 0.163 0.178
24 0.200 0.121 0.136 0.151 0.166 0.181
25 0.200 0.123 0.138 0.153 0.168 0.183
26 0.200 0.125 0.140 0.155 0.170 0.185
27 0.200 0.127 0.142 0.157 0.172 0.187
28 0.200 0.129 0.144 0.159 0.174 0.189
29 0.200 0.130 0.145 0.160 0.175 0.190
30 0.210 0.131 0.146 0.161 0.176 0.191
31 0.210 0.132 0.147 0.162 0.177 0.192
32 0.210 0.134 0.149 0.164 0.179 0.194
33 0.210 0.135 0.150 0.165 0.180 0.195
34 0.210 0.136 0.151 0.166 0.181 0.196
35 0.210 0.138 0.153 0.168 0.183 0.198
36 0.210 0.140 0.155 0.170 0.185 0.200
37 0.220 0.142 0.157 0.172 0.187 0.202
38 0.220 0.144 0.159 0.174 0.189 0.204
39 0.220 0.147 0.162 0.177 0.192 0.207
40 0.230 0.151 0.166 0.181 0.196 0.211
41 0.230 0.155 0.170 0.185 0.200 0.215
42 0.230 0.160 0.175 0.190 0.205 0.220
SD, standard deviation.
From Chervenak and colleagues, 1984,
28
with permission.
percentile. Hypotelorism has been associated with chromosomal anomalies (trisomy 13, trisomy 21, 18p–, 5p–,
and 14q +), holoprosencephaly, Meckel-Gruber syndrome,
microcephaly, maternal phenylketonuria, and others.
32 – 34
Hypertelorism can occur as an isolated defect but has
also been associated with a long list of malformations
and syndromes, such as frontal, ethmoidal, or sphenoidal
meningoencephalocele; median cleft syndrome; and craniosynostosis.
Mayden and associates
orbital measurements as a function of the BPD, which
34
31
developed nomograms of
are taken as a classical reference to which newer data are
compared ( Table 3–11 ). Nomograms for orbital diameters
as a function of age have been published because the
Figure 3–3.
Chapter 3 Biometry of the Fetal Brain
OOD
IOD
OD
Table 3–11. NOMOGRAM FOR EVALUATION OF THE INNER AND OUTER ORBITAL
DIAMETERS IN THE FETUS VERSUS BIPARIETAL DIAMETER
119
Biparietal
Diameter (cm)
1.9 0.5 1.3
2.0 0.5 1.4
2.1 0.6 1.5
2.2 0.6 1.6
2.3 0.6 1.7
2.4 0.7 1.7
2.5 0.7 1.8
2.6 0.7 1.9
2.7 0.8 2.0
2.8 0.8 2.1
2.9 0.8 2.1
3.0 0.9 2.2
3.1 0.9 2.3
3.2 0.9 2.4
3.3 1.0 2.5
3.4 1.0 2.5
3.5 1.0 2.6
3.6 1.0 2.7
3.7 1.1 2.7
3.8 1.1 2.8
Inner Orbital
Diameter (cm)
Outer Orbital
Diameter (cm)
(continued)