26. The
following are true of second trimester biochemical screening e.g. the "Bart
| a. | it screens for all chromosomal abnormalities | |
| b. | it screens for Down's syndrome but not neural tube defects | |
| c. | it is best done at 12 - 14 weeks | |
| d. | it is close to 100% accurate in detecting Down's syndrome | |
| e. | it is based on the assay of maternal AFP, HCG and thyroid hormones | |
| f. | it shows a unique pattern in the presence on Trisomy 18 | |
| g. | will be the recommended method of screening from April 2010 |