The current maternal blood-screening test is called the triple screen because:

The current maternal blood-screening test is also known as the triple screen test because of the testing of the three substances in the blood of a pregnant woman. These three tested components are the hCG (Human Chorionic Gonadotropin), AFP (Alpha-feto protein), and the estriol.

For the purpose of this triple screen test, the blood is drawn for the expectant mother and then this drawn blood is tested for the listed three components.

Hence, the correct answer is 'it tests for three substances in the maternal blood'.

Transcription doesn't have to be as accurate as replication. The answer is simple that transcripts can not be store permanently. And so it is not accurate. as far as the question of the accuracy of replication concern, it is consider more accurate because of the following steps taking place in this process:
1) high selectivity of DNA polymerase 
2) exonucleatic proofreading