The fetal fibronectin test is supposed to predict with an accuracy of 99.5% (or stats close to that, can't remember exactly) whether you are likely to go into labour within two weeks.
I had the test done three weeks ago after experiencing regular tightenings at 26 weeks pregnant. It was negative and was assured the test was virtually infallible and there was no way I'd be having a baby in the next 14 days.
A week later, at 27 weeks, I had the baby. He weighs 2lbs and is luckily doing well. Due my my panicky hysteria I had the steroids but had I trusted the doctors it could all be different.