Ultrasonic Assessment of Fetal Size and Growth
with particular reference to
fetal biometry and measuring accuracy in the first and third trimester of pregnancy
and
a comparison of fetal size in Caucasian and Chinese immigrant women both with and without gestational diabetes mellitus.
A Thesis
Submitted to the Faculty of Medicine
at the
University of Sydney
by
Susan Lyn Campbell Westerway MAppSc (MRT)
0054087 KB
In fulfilment of the requirements for the award of
Doctor of Philosophy
“ Knowledge of fetal size has two main applications in obstetric practice. The first is to compare the size of a fetus of unknown gestational age with normal figures and so obtain an estimate of the maturity of the fetus. The second application is to compare the size of a fetus of known gestational age with known normals either as a single reading to tell whether the fetus in question is larger or smaller than normal or, better, as a series of readings. A series of readings is to be preferred since it not only checks the accuracy of a single reading but also gives most useful information as to the rate of growth of the fetus.”
William Garrett and Dave Robinson (1971)
Pioneers of Australian Ultrasound
ABSTRACT
This work investigates a number of issues. Firstly it examines ultrasonic fetal biometry, the parameters and techniques for accurate measuring and reviews the procedure adopted for graph formation and application of regression analysis for a mathematical model to describe the relationship between fetal size and weeks of gestation. Next it establishes new Australian fetal measurement charts for the crown rump length, head circumference and abdominal circumference, based on an Australian population, to replace the charts currently in use that are over 20 years old and relate to middle class white American and British women. The new graphs, along with previous work completed by the author in 1999 on the BPD, OFD femur and humerus length, were subsequently accepted by the Australasian Society for Ultrasound in Medicine (ASUM) in 2001 as the new Australian standard for ultrasonic fetal measurements. The accuracy of first trimester ultrasound dating is also investigated, displaying the variations seen in the crown-rump length due to fetal flexion and the implications of inaccurate measuring. The third study examines inter- and intra-sonographer ultrasonic fetal measurement reproducibility in the final 6 weeks of pregnancy. The study highlights the importance of sonographer competence, standardised measuring protocols, image planes and reference charts, particularly for patients undergoing ultrasound examinations for fetal growth assessment at different practices.
The fourth study looks at the incidence of fetal macrosomia and birth complications in Chinese women and Caucasian women in two time periods, 1992 and 1999/2000. The results showed a rise in macrosomic babies born to Chinese immigrants from 4% of total Chinese births in 1992 to 9.8% in 1999/2000. There was also a rise in the rate of macrosomia among Caucasian women with respective rates of 11 and 14% for the same periods. The incidence of post partum haemorrhage increased significantly over this time in both Chinese immigrant and Caucasian women. Interventions declined in all Caucasian birth-weight ranges whilst interventions for Chinese births remained stable except between 3500grams and 4000grams, where interventions rose from 35.7% to 60.5%.
Fetal macrosomia is a complication of pregnancy that is increasing in incidence. One of the causes of fetal overgrowth is uncontrolled gestational diabetes mellitus and so if women thus diagnosed are closely monitored, the risks of a macrosomic baby and associated birth complications may be reduced. The final study examines the effect of gestational diabetes mellitus (GDM) on fetal growth. GDM is a complication of mid to late pregnancy caused by glucose intolerance. In the Australian population up to 8% of all pregnancies can be affected. In the Australian Chinese community the GDM rate is as high as 15% compared with 4% in Caucasian women. The risks to the fetus as a result of GDM include increased perinatal mortality, large for gestational dates, macrosomia and prematurity. The aim of this study was to determine whether the fetuses of women diagnosed with GDM were significantly larger for dates for any of the commonly ultrasonically measured fetal parameters, than in the general pregnant population. The results show that if the glycaemic levels are properly controlled, fetal size should not be compromised. The abdominal circumference measurement appears to be the important marker for fetal macrosomia, particularly in the Chinese population. The study also assessed fetal weight gain from 36 weeks gestation to term in Caucasian women with GDM and Chinese pregnancies both with and without GDM. No statistically significant difference was seen in daily weight gain between the groups investigated.
DECLARATION
I hereby declare that this thesis is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person except where due acknowledgment is made in the text of this thesis.
Signature ………………………………………………
Dated this …………………………… day of ……………….…………
Two thousand and five
PUBLISHED ARTICLES & PRESENTATIONS AT SCIENTIFIC MEETINGS ARISING FROM THIS THESIS
1 Ultrasonic Fetal Measurements: New Australian standards for the new millennium.
Original Article:
Australian and New Zealand Journal of Obstetrics and Gynaecology 2000; 40 (3): 297-302.
2 Fetal Biometry in Australia
Original work – invited speaker - presented at:
The 11th Annual Conference of the Australian Sonographers Association
Melbourne, Vic, May 2004.
3 Crown Rump Length Measurements for Accurate Dating (Appendix 1)
Original work presented at:
a. 32nd Annual Scientific Meeting Australasian Society of Ultrasound in Medicine, Brisbane Queensland, September 2002.
b. 12th Annual Conference of the Australian Sonographers Association
Brisbane, Queensland, May 2005.
4 Crown Rump Length Measurements for Accurate Dating
Original Article:
Ultrasound Bulletin 2002 5,4:17.
5 The Accuracy of Dating Ultrasound in the First Trimester
Original work – invited speaker - presented at:
12th Annual Conference of the Australian Sonographers Association
Brisbane, Queensland, May 2005.
6 Third Trimester Measurements - Inter/Intra-Sonographer Evaluation of Accuracy.
Co-authors: Rob Heard, Jonathan Morris.
Original work presented at:
a. 9th World Congress of Ultrasound in Obstetrics and Gynaecology,
Melbourne, Victoria, October 2001.
b. Medical Imaging Australasia Interprac
Guest Speaker
Sydney October 2001.
c. 9th Annual Conference of the Australian Sonographers Association, Sydney, NSW, May 2002.
7 Incidence of Fetal Macrosomia and Birth Complications in Chinese Immigrant Women.
Co-authors: Jonathan Morris, John Keogh and Rob Heard.
Original Article:
Australian and New Zealand Journal of Obstetrics and Gynaecology 2003; 43 (1): 46-49.
8 Third Trimester Measurements for Weight Evaluation
Co-authors: Rob Heard, Jonathan Morris.
Original Article:
Sound Effects: Volume 3, 2004
9 Incidence of Fetal Macrosomia and Birth Complications in Chinese Immigrant Women. (Appendix 2)
Co-authors: Jonathan Morris, John Keogh and Rob Heard.
Original work presented at:
a. 10th Annual Scientific Meeting of the Australian and New Zealand Perinatal Society, Canberra, March 2001 (Appendix 3).
b. 35th Annual Scientific Meeting Australasian Society of Ultrasound in Medicine, Adelaide, SA, September 2005.
10 The Effect of Gestational Diabetes Mellitus on Fetal Growth. (Appendix 3)
Co-authors: Rob Heard, Jonathan Morris.
Original work presented at:
a. 33rd Annual Scientific Meeting of Australasian Society of Ultrasound in
Medicine. Perth, WA, September 2003.
b. 11th Annual Conference of the Australasian Sonographers Association, Melbourne, Victoria, May 2004.
c. 7th Congress of the Asian Federation of Societies for Ultrasound
in Medicine and Biology:
77th Annual Scientific Meeting of the Japan Society of Ultrasound.
29th Annual Meeting of the Japanese Society of Sonographers.
Utsunomiya, Tochigi, Japan. May 2004.
11 Comparison of the Incidence of Fetal Macrosomia, Birth Complications,
Birth Weight Differences and Fetal Growth Patterns Between Caucasians and Chinese Pregnancies.
Original work – invited speaker - presented at:
35th Annual Scientific Meeting of Australasian Society of Ultrasound in Medicine. Adelaide, South Australia, September 2005.
12 How Are Fetal Biometry Graphs Formulated?
Original Article:
Sound Effects: Volume 4, 2005
ACKNOWLEDGEMENTS
Medical research by a sonographer can be very difficult without the co-operation of employers and supervisors. This project would not have been possible had it not been for Professor Jonathan Morris from the Northern Clinical School at Royal North Shore Hospital, agreeing to take on a non-medical student and guide me through a most daunting experience. His dedication to all his students makes him an exceptional person. My gratitude must also go to my other supervisor, Dr Rob Heard for his invaluable statistical input with suggestions, checking and rechecking of figures and graphs and the ability to help me calmly reply to adverse reviewers comments for journal articles.
I would particularly like to thank the midwives at the antenatal clinics at both the Hornsby Ku-Ring-Gai Hospital and the Royal North Shore Hospital for their patience and acceptance of an extra body, and ultrasound machine, in already cramped clinics. Dr John Keogh and Carolyn Smith for inspiration for the macrosomia work and Rosemary Hitchman who helped recruit GDM patients at RNSH. Catriona Andronicos from the OBSTET Data base gave freely of her time to download countless requested statistics. North Shore Obstetric and Gynaecologic Ultrasound, Medical Imaging Australasia (MIA) and Philips Medical Systems assisted me financially by way of sponsorship to attend conferences where I presented works in progress. This invaluable experience would not have been possible without their assistance.
To my precious family - Gary, Kate and Amy, who have been my inspiration and kept me focused over the years of research and made it all worthwhile – my love, devotion and gratitude.
TABLE OF CONTENTS
Chapter 1 BACKGROUND & LITERATURE REVIEW
1.1 Introduction 1
1.2 Fetal Growth 2
1.2.1 The Small for Gestational Age Fetus 4
1.2.2 The Large for Gestational Age Fetus 5
1.3 Clinical Evaluation of Fetal Size and Growth 6
1.3.1 Predictors and Consequences of Excessive Growth 7
1.3.2 Maternal Risks 9
1.3.3 Fetal Complications 10
1.3.4 Neonatal Risks 11
1.4 Macrosomia 11
1.5 Fetal Growth and Gestational Diabetes Mellitus 13
1.6 Ultrasonic Evaluation of Pregnancy 19
1.7 Safety of Ultrasound 23
1.8 Variability in Gestational Age and Fetal Growth 24
1.9 Ultrasonic Determination of Macrosomia 29
1.10 Fetal Size / Growth and Ethnicity 32
1.11 Measurements of Fetal Parameters for Growth/Weight Assessment
1.11.1 The BPD, OFD and Head Circumference 36
1.11.2 Abdominal Circumference 39
1.11.3 The Femur and Humerus 40
1.11.4 Fetal Weight Assessment 42
1.12 Importance of Ultrasound in the Third Trimester of Pregnancy 44
1.12.1 The Placenta and Umbilical Cord Doppler 45
1.13 Mathematical Modelling 47
1.14 Summary of the Literature 49
1.15 Justification for the Study 51
1.16 Objectives of the Study 53
Chapter 2 ULTRASONIC FETAL BIOMETRY
2.1 Introduction 55
2.2 Measurement of Fetal Parameters 59
2.2.1 Sac Volume 60
2.2.2 The Crown Rump Length 61
2.2.3 The Biparietal Diameter, Occipito Frontal Diameter
And Head Circumference 62
2.2.4 The Abdominal Circumference 66
2.2.5 The Femur and Humerus Lengths 67
2.3 Data Analysis and Graph Creation 69
2.3.1 Longitudinal versus Cross Sectional Analysis 70
2.3.2 Raw Data 71
2.3.3 Regression Analysis 72
2.3.4 Standard Deviations and Confidence Intervals 74
2.4 Establishing New Fetal Measurement Charts 76
2.4.1 2000 CRL Data 77
2.4.2 2000 Head Circumference Measurements 83
2.4.3 2000 Abdominal Circumference Measurements 86
2.5 2001 ASUM Fetal Measurement Charts 90
2.6 ASUM Graph Comparisons 92
2.6.1 BPD Comparison ASUM 2001/Hadlock 1984 93
2.6.2 Head Circumference Comparison
ASUM 2001/Hadlock 1984 94
2.6.3 Abdominal Circumference Comparison
ASUM 2001/Deter 1982 95
2.6.4 Humerus Length Comparison ASUM 2001/Jeanty 1984 96
2.6.5 Femur Length Comparison ASUM 2001/Hadlock 1984 97
2.7 The Accuracy of Dating Ultrasound in First Trimester 98
2.7.1 First Trimester Dating Accuracy Protocol 99
2.7.2 Crown Rump Length Measurement 100
2.7.3 First Trimester Head, Abdominal
and Long Bone Measurements 101
2.7.4 First Trimester Measurements Accuracy Results 102
2.7.5 CRL Measuring Problems 105
2.7.6 CRL, Fetal Flexion and Nuchal Translucency 108
2.7.7 First Trimester Measuring Accuracy Summary 109
2.8 Chapter Summary 110
Chapter 3 THIRD TRIMESTER MEASUREMENTS -
an Inter/Intra Sonographer Evaluation of Accuracy
3.1 Introduction 111
3.2 Aims of Objective Two 114
3.3 Methodology 114
3.4 Results 115
3.4.1 BPD, OFD and Head Circumference 116
3.4.2 Abdominal Circumference 118
3.4.3 Femur Length 119
3.4.4 Fetal Weight Estimation 120
3.4.5 Intra-Sonographer Results 121
3.5 Discussion 122
3.6 Quality Control in the Third Trimester 126
Chapter 4 The Incidence of Fetal Macrosomia and Birth Complications
in Caucasian and Chinese Immigrant Women
4.1 Introduction 127
4.2 Aims of Objective Three 129
4.3 Methodology – Inclusion Criteria and Definitions 129
4.3.1 OBSTET Data Base 130
4.4 Results
4.4.1 Birth Weight and Macrosomia 131
4.4.2 Post Partum Haemorrhage and Intervention 131
4.4.3 Haemoglobin Levels 136
4.5 Discussion 137
Chapter 5 Ultrasound Prediction of At Risk Birth Weight in Chinese
and Caucasian Fetuses in Normal Pregnancy and those
Complicated by Gestational Diabetes Mellitus
5.1 Introduction……………………………………………………..140
5.2 ASUM Vs Queen Mary Abdominal Circumference………….…142
5.3 Aims of Objective Four………………………………………....144
5.4 Patient Selection Criteria………………………………………. 144
5.5 Subject Information Statement and Patient Consent……………146
5.6 The Patient Questionnaire………………………………………146
5.7 Choosing the Ultrasonic Fetal Parameters……………………...147
5.8 Safety of Repeated Ultrasound Scans…………………………..149
5.9 Methodology……………………………………………………150
5.9.1 Fetal Parameters…………………………………………..151
5.9.2 The Data Collection Sheet Design………………………..152
5.9.3 Statistical Analysis………………………………………..153
5.10 Results…………………………………………………………..154
5.10.1 Chinese with and without GDM………………………...156
5.10.2 Caucasians with GDM…………………………………..158
5.10.3 Graph Comparison – Caucasians/Chinese………………159