The aim of this study was to examine the association between biological, behavioural and lifestyle risk factors and risk of miscarriage. Six hundred and three women aged 18–55 years whose most recent pregnancy had ended in first trimester miscarriage (<13 weeks of gestation; cases) and 6116 women aged 18–55 year whose most recent pregnancy had progressed beyond 12 weeks (controls) were questioned about socio-demographic, behavioural and other factors in their most recent pregnancy. Consumption of chocolate daily or on most days was associated with reduced odds of miscarriage (odds ratio = 0.81).
http://onlinelibrary.wiley.com/doi/10.1111/j.1471-0528.2006.01193.x/pdf
Alcohol, Dairy, Dietary Fat, Eggs, Fiber, Fruit, L-Arginine, Meat, Methionine, Soy, Vegetables
For a concise list of qualities found to affect one's risk of miscarriage, see: Causes of Miscarriage