20. Ultrasound Scan.
| a. | gestation assessment in the 1st. trimester is by measurement of the bi-parietal diameter | |
| b. | nuchal fold thickness measurement should not be done until at least 18 weeks | |
| c. | nuchal fold thickness measurement allows identification of 90% of Downs' pregnancies | |
| d. | an 18 week scan will diagnose placenta previa in 90% of cases | |
| e. | a scan at 28 weeks will accurately determine gestational age | |
| f. | scanning for fetal cardiac anomalies is best done between 16 & 18 weeks | |
| g. | ultrasound scan can measure blood flow in umbilical vessels | |
| h. | ultrasound scanning at 18 weeks will identify almost all cases of Potter's syndrome |