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Mani Montazemi, RDMS
Obstetrical Measurements
Obstetrical
Measurements
Mani Montazemi, RDMSDirector of Ultrasound Education & Quality Assurance
Baylor College of Medicine
Division of Maternal-Fetal Medicine
Department of Obstetrics and Gynecology
Texas Children’s Hospital, Pavilion for Women
Houston Texas
Mani Montazemi, RDMS
Obstetrical Measurements
First Trimester Ultrasound
• Mean Gestational Sac Diameter
• Crown Rump Length
• Embryonic Cardiac Activity
• Yolk Sac
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Anembryonic Gestation “Blighted Ovum”
MSD ≥ 25mm “No embryonic pole”
Peter M. Doubilet, Carol B Benson et al,
N Engl J Med 2013; 369:1443-51
Early Pregnancy Failure
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Crown-Rump Length
• Embryonic length
• Most accurate US measurement for estimation
of gestational age (+/- 5-7 days)
– especially between 6 - 9 weeks
Crown-Rump Length
**
Mani Montazemi, RDMS
Obstetrical Measurements
**
Mani Montazemi, RDMS
Obstetrical Measurements
Avoid Inaccurate CRLCaution
*
*
*
*
?
Mani Montazemi, RDMS
Obstetrical Measurements
1st Trimester (GS & CRL)
• Qualitative
– Small, tight GS relative to size of embryo
• Quantitative
– MSD-CRL
• Normal if > 5 mm (92%)
• Abnormal if < 4mm (94% miscarriage)
Mani Montazemi, RDMS
Obstetrical Measurements
• Qualitative
– Small, tight GS relative to size of embryo
• Quantitative
1st Trimester (GS & CRL)
Mani Montazemi, RDMS
Obstetrical Measurements
• Qualitative
– Small, tight GS relative to size of embryo
• Quantitative
1st Trimester (GS & CRL)
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Mani Montazemi, RDMS
Obstetrical Measurements
1st Trimester (GS & CRL)
Mani Montazemi, RDMS
Obstetrical Measurements
• Qualitative
– Small, tight GS relative to size of embryo
• Quantitative
– ( MSD – CRL )
• Normal if > 5 mm (92%)
• Abnormal if < 4mm (94% miscarriage)
Peter M. Doubilet, Carol B Benson et al,
N Engl J Med 2013; 369:1443-51
Bromley, et. al. 1991
Kurtz et. al. 1992
1st Trimester (GS & CRL)
CRL Measurements
TRV vs. SAG
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
ML
Mani Montazemi, RDMS
Obstetrical Measurements
ML
RT
Mani Montazemi, RDMS
Obstetrical Measurements
RT
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Mani Montazemi, RDMS
Obstetrical Measurements
1st Trimester
• Estimates of CRL which are poor estimates should be excluded from the mean CRL
• Gestational age should not be an average of that based on MSD and CRL
• EDD is determined on the initial first trimester ultrasound based on CRL and SHOULD NOT BE CHANGED based on subsequent ultrasounds
Mani Montazemi, RDMS
Obstetrical Measurements
CRL = 6.2 mm
Mani Montazemi, RDMS
Obstetrical Measurements
Embryonic Cardiac Activity
• Should have visible heart beat CRL ≥ 7mm
Peter M. Doubilet, Carol B Benson et al,
N Engl J Med 2013; 369:1443-51
Embryonic Cardiac Activity
• Bradycardia < 80 bpm: poor prognosis
• Absence may be NL in embryos < 4 mm
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Embryonic Cardiac Activity
Mani Montazemi, RDMS
Obstetrical Measurements
Embryonic Cardiac Activity
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Caution
In keeping with the ALARA principle, M-mode
should be used instead of spectral Doppler
to document embryonic heart rate
Mani Montazemi, RDMS
Obstetrical Measurements
Time-averaged acoustic intensity
delivered to the fetus is lower
with M-mode than with spectral Doppler
Mani Montazemi, RDMS
Obstetrical Measurements
“Don’t”
Mani Montazemi, RDMS
Obstetrical Measurements
Diagnostic Challenge
Mani Montazemi, RDMS
Obstetrical Measurements
Embryonic Yolk Sac
•
Normal
Aust. N Z J Obstet Gynaecol 2006 Oct;46(5):413-8
J Perinat Med. 1999;27(4):316-20
Radiology April 1992 183:1 115-118
Mani Montazemi, RDMS
Obstetrical Measurements
Embryonic Yolk Sac
Mani Montazemi, RDMS
Obstetrical Measurements
Embryonic Yolk Sac
“Don’t”
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Embryonic Yolk Sac
“Outer To Outer”
* *
Aust. N Z J Obstet Gynaecol 2006 Oct;46(5):413-8
J Perinat Med. 1999;27(4):316-20
Radiology April 1992 183:1 115-118 Mani Montazemi, RDMS
Obstetrical Measurements
Increased NT
• Chromosome abnormalities
– (T13, T18, T21, XO)
• Cardiac defects
• Genetic syndromes
• Skeletal dysplasias
• Miscarriage
• Discordance of NT in monochorionic twins is
an early marker for TTTS
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Embryonic Yolk Sac
Mani Montazemi, RDMS
Obstetrical Measurements
Embryonic Yolk Sac 2nd & 3rd Trimester Measurements
• Biparietal diameter
• Head circumference
• Lateral atrial ventricular diameter
• Transverse cerebellar diameter
• Cisterna magna
• Nuchal fold (16 to 20 weeks)
• Abdominal circumference (including skin)
• Femur diaphysis length
• Humerus diaphysis length
Mani Montazemi, RDMS
Obstetrical Measurements
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Mani Montazemi, RDMS
Obstetrical Measurements
• Determine Gestational Age
– BPD / HC
– AC
– FL
– HL
Imaging Parameters
For a Standard Fetal Examination
2nd & 3rd Trimester
How does this age compare to menstrual dates?
How the head, body & femur correspond to each other?
Measurements & ultrasound age need to be correlated
Mani Montazemi, RDMS
Obstetrical Measurements
Head Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Biparietal Diameter
• After CRL, BPD is next most reliable US
parameter for age prediction
• Accuracy decreases as pregnancy advances,
especially after 26 weeks
Thalamic View
Mani Montazemi, RDMS
Obstetrical Measurements
Abnormal Head Shape
DolicocephalicBrachycephalic
(larger BPD) (smaller BPD)
Mani Montazemi, RDMS
Obstetrical Measurements
Cephalic Index“Ratio used to evaluate head shape”
Mani Montazemi, RDMS
Obstetrical Measurements
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Cephalic Index
• CI = BPD/FOD x 100
– Normal range
• At 1SD = 74-83
• At 2SD = 70-86
– Dolicocephalic CI < 70
– Brachycephalic CI > 86
Short
AxisLong
Axis
Hadlock et al AJR 137 1981
“Ratio used to evaluate head shape”
BPD
FOD
Mani Montazemi, RDMS
Obstetrical Measurements
“Cephalic Index”
* *
BPD / FOD x 100
MidMid
Mani Montazemi, RDMS
Obstetrical Measurements
Caution
Mani Montazemi, RDMS
Obstetrical Measurements
Caution
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
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BPD / FOD x 100
BPD 3.17cm
FOD 4.11cm
BPD / FOD x 100
Mani Montazemi, RDMS
Obstetrical Measurements
Abnormal Head Shape
• What should you use?
– Area corrected BPD
– Head circumference
Mani Montazemi, RDMS
Obstetrical Measurements
Area Corrected BPD
• Calculate when CI is ≤ 70 or ≥ 86
• Corrects BPD to an ideal head shape
Doubilet PM, Greenes RA, AJR, 142:797-800, 1984
Mani Montazemi, RDMS
Obstetrical Measurements
Head Circumference
• HC takes into account the shape of the head
• When properly done, HC is a reliable measurement
for gestational dating
• HC is measured at the same level a BPD, around the
outer perimeter of the bony calvarium, excluding
subcutaneous tissues of the skull
Mani Montazemi, RDMS
Obstetrical Measurements
Head Measurements
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Mani Montazemi, RDMS
Obstetrical Measurements
Diagnostic Challenge
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
How to Locate the Atrium?
Mani Montazemi, RDMS
Obstetrical Measurements
How to Locate the Atrium?
• The glomus of the choroid plexus…
– Easy to identify but not a reliable anatomic landmark to
locate atrium
• Location of the glomus may change depending
– On the shape of choroid plexus
– On the degree of dilatation of ventricle
• Neuro-anatomy suggest a more reliable landmark
– Internal parieto-occipital sulcus
Mani Montazemi, RDMS
Obstetrical Measurements
How to Locate the Atrium?
• The glomus of the choroid plexus…
– Easy to identify
• Location of the glomus may change depending
– On the shape of choroid plexus
– On the degree of dilatation of ventricle
• Neuro-anatomy suggest a more reliable landmark
– Internal parieto-occipital sulcus
Mani Montazemi, RDMS
Obstetrical Measurements
How to Locate the Atrium?
• The glomus of the choroid plexus…
– Easy to identify but not a reliable anatomic landmark to
locate atrium
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How to Locate the Atrium?
• Location of the glomus may change depending
– On the shape of choroid plexus
– On the degree of dilatation of ventricle
Guibaud - ISUOG
Ultrasound Obstet Gynecol.2009; 34: 127–130
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
How to Locate the Atrium?
• Location of the glomus may change depending
– On the shape of choroid plexus
– On the degree of dilatation of ventricle
• Neuro-anatomy suggest a more reliable landmark
– Internal parieto-occipital sulcus
Guibaud - ISUOG
Ultrasound Obstet Gynecol.2009; 34: 127–130
• Anterior landmark: cavum septi pellucidi or columns of fornix
• Posterior landmark: ambient cistern (echogenic triangular area)
• Measurement: performed opposite the internal parieto-occipital sulcus
T
T
Internal Parieto-occipital Sulcus
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Internal Parieto-occipital Sulcus Transcerebellar Plane
Mani Montazemi, RDMS
Obstetrical Measurements
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Cerebellar View – Cerebellum Shape
Mani Montazemi, RDMS
Obstetrical Measurements
Cerebellar View – Cisterna Magna
• Size: 2-10 mm
< 2 mm spina bifida (ACII)
> 10 mm Dandy-Walker
T
T
P
P
CSP
FH
FH
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
land marks are not well visualized
column of fornix instead of CSP
too much atrium of the LV seen
Mani Montazemi, RDMS
Obstetrical Measurements
scanning plane is off axis
orbits are visualized
Mani Montazemi, RDMS
Obstetrical Measurements
land marks are not well visualized
Mani Montazemi, RDMS
Obstetrical Measurements
land marks are not well visualized
scanning plane is off axis
orbits are visualized
petrous & sphenoid bones are seen
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Mani Montazemi, RDMS
Obstetrical Measurements
Abdominal Circumference
• Not used for dating a pregnancy
• Used for estimation of fetal weight
– Detection of growth restriction & macrosomia
• Compared to fetal head size for symmetry
Mani Montazemi, RDMS
Obstetrical Measurements
Abdominal Circumference
• Measure across entire abdomen
• Perpendicular to spine
– Do not oblique
How to measure?
Mani Montazemi, RDMS
Obstetrical Measurements
Abdominal CircumferenceHow to measure?
Mani Montazemi, RDMS
Obstetrical Measurements
Junction of the Umbilical Vein
and Portal Sinus Not Demonstrated
Mani Montazemi, RDMS
Obstetrical Measurements
Abdominal CircumferenceScanning Techniques
Mani Montazemi, RDMS
Obstetrical Measurements
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Mani Montazemi, RDMS
Obstetrical Measurements
?
Mani Montazemi, RDMS
Obstetrical Measurements
Abdominal Circumference
Mani Montazemi, RDMS
Obstetrical Measurements
Abdominal Circumference
Mani Montazemi, RDMS
Obstetrical Measurements
HC:AC Ratio
• Varies with gestational age
• Ratio is approximately 1:1
– Range of means: from 1.23 at 13-14 weeks to 0.96
at 41-42 weeks
• Ratio decreases with age
• BPD growth slows
• Abdominal growth continues
Mani Montazemi, RDMS
Obstetrical Measurements
If you are certain of GA based on the earlier
study then the ratio is valuable
HC/AC Ratio
GA (weeks) Mean 5th to 95th percentile
13 – 14 1.23 1.14 to 1.31
15 – 16 1.22 1.05 to 1.39
17 – 18 1.18 1.07 to 1.29
19 – 20 1.18 1.09 to 1.39
21 – 22 1.15 1.06 to 1.25
------ ----- -----
33 – 34 1.04 0.96 to 1.11
35 – 36 1.02 0.93 to 1.11
37 – 38 0.98 0.92 to 1.05
39 – 40 0.97 0.87 to 1.06
41 – 42 0.96 0.93 to 1.00
Campbell Br J Obstet Gynecol 84:165-174, 1977 Mani Montazemi, RDMS
Obstetrical Measurements
Abdominal Circumference
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Mani Montazemi, RDMS
Obstetrical Measurements
Femoral Length
• Length of femoral shaft (diaphysis)
• Do not include distal “epiphyseal spur”
Knee
Hip
Mani Montazemi, RDMS
Obstetrical Measurements
Femur Length
1. Focal zone @ appropriate level
2. Image magnified appropriately
3. Whole femur diaphysis imaged
4. US beam perpendicular to long axis of femur
5. Caliper placed @ each end of ossified diaphysis
6. Longest visible diaphysisis measured
7. Spur artifacts on end of diaphysis not included in
measurement
Mani Montazemi, RDMS
Obstetrical Measurements
Humerus
Mani Montazemi, RDMS
Obstetrical Measurements
Humerus Length
Mani Montazemi, RDMS
Obstetrical Measurements
Mani Montazemi, RDMS
Obstetrical Measurements
Fetal Weight
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Mani Montazemi, RDMS
Obstetrical Measurements
Estimated Fetal Weight
• Should include at least the following three
fetal parameters
– Head, Abdomen & Femur
Mani Montazemi, RDMS
Obstetrical Measurements
Estimated Fetal Weight
• In general US accuracy is 15-20% (95 %
confidence range)
• Remember that you are not dealing with an
absolute number
Mani Montazemi, RDMS
Obstetrical Measurements
Estimated Fetal Weight
• In general US accuracy is 15-20% (95 %
confidence range)
• Remember that you are not dealing with an
absolute number
– (± 15% of 4000 gm is 600 gm (3400-4600 gm)
Mani Montazemi, RDMS
Obstetrical Measurements
Estimated Fetal Weight
For estimated fetal weight
to have clinical value,
one must know the
gestational age to obtain
weight percentile
Very Important!
Mani Montazemi, RDMS
Obstetrical Measurements
Neonatal Weight
GA
(week)
5th 10th 25th 50th 75th 90th 95th
33 1422 1519 1696 1918 2169 2421 2587
34 1608 1714 1906 2146 2416 2687 2865
35 1804 1919 2125 2383 2671 2959 3148
36 2006 2129 2349 2622 2927 3230 3428
37 2210 2340 2572 2859 3177 3493 3698
38 2409 ( 2544 2786 3083 3412 3736 ) 3947
39 2595 2735 2984 3288 3622 3952 4146
40 2762 2904 3155 3462 3798 4127 4340
Weight Percentile (g)
Doubilet et al, J Ultrasound Med 16: 241-249, 1997 Mani Montazemi, RDMS
Obstetrical Measurements
Interval Growth Rate
Scans for growth evaluation
can typically be performed
at least 3 weeks apart
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Mani Montazemi, RDMS
Obstetrical Measurements
Fetal Growth
Mani Montazemi, RDMS
Obstetrical Measurements
Fetal Growth
Mani Montazemi, RDMS
Obstetrical Measurements
Fetal Growth
Mani Montazemi, RDMS
Obstetrical Measurements
Fetal Growth
Mani Montazemi, RDMS
Obstetrical Measurements
Fetal Growth
Mani Montazemi, RDMS
Obstetrical Measurements
Obstetrical
Measurements
Thank You