Hey guys
Here is an interesting study from Obstetrics and Gynecology that interviewed 1900 women in their 7th month of pregnancy. What they found was that in about 9 percent of the women who worked nights in their first trimester had a 50 percent increased risk of premature labor.
Now obviously we need more studies to examine this issue but it does raise an important issue about avoiding grave-yard shifts during pregnancy.

Obstet Gynecol, December 2005