Stillbirth is a major problem in wealthy nations, and overweight or obese women have higher risks than lean women. 
Consistent with the evidence indicating that high fat diets increase blood coagulation activity, researchers have found that a high fat diet probably decreases blood flow to the placenta, increasing the risk of stillbirth (abstract).
The high fat diet produced a 38-56% decrease in blood flow from mother to placenta. It also increased inflammatory markers.
Do you think this could also cause other pregnancy complications? The authors of this study think so.
OK, I know some will object that this was done on Japanese macques, not humans. The researchers chose macques because they have a placental structure similar to humans. Genetically, macques have DNA 93% similar to humans.