Are alcohol tests for expectant mothers a good idea?

Expectant mothers are told not to drink, but many will take a sip or two of something over the course of a pregnancy.
Since alcohol can pose a serious risk to foetal development, Homerton Hospital in east London has for the past year been trialling a blood test for pregnant women that claims to show how much they have been drinking. The problem is that research on CDT blood tests has assessed mostly male heavy drinkers. There has been precious little work done on women, though we do know that the test becomes unreliable in females using oral contraceptives and in people who are overweight and obese.