There's a lot of research out there about factors that seem correlated to risk of miscarriage, and in most cases, researchers have not quite sorted out which risk factors actually cause miscarriage and which risk factors merely have statistical associations with miscarriage.
A good example of this is the occasional media frenzy over the association between drinking coffee during pregnancy and miscarriage. The truth could be that caffeine causes miscarriages or women who are likely to miscarry are more likely to drink coffee during pregnancy.
With that in mind, let's take a look at the subject of body weight and miscarriage. There has been a lot of research on the link, and it seems fairly clear that obesity is a risk factor for miscarriage. Does obesity, though, actually cause miscarriage? That's certainly up for debate.
Body weight is a sensitive subject for most people. Very few women in the United States are satisfied with their bodies. Many women struggle with their weight for their entire lives, sometimes facing depression, anxiety and low self-esteem, because of the ceaseless internal and external pressure to lose weight. Almost everyone who is overweight is well aware of the matter and does not need to be told about the health risks of being overweight.
In addition, many women are tempted to blame themselves for their miscarriages in the absence of a clear cause -- so a link between obesity and miscarriage makes an already emotionally charged issue even more so.