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.