Women are naturally heavier now, and while I have known one woman who actually lost weight while pregnant, it was in part because she was a bigger lady who had a significant amount of weight to lose.  This being said, apparently 2/3 of women are overweight at this point in time.  This means that pregnant women are also heavier than ever, and frankly there are already enough risks with pregnancy in general.  But the excess weight is linked to heart disease, diabetes, and high blood pressure, which are often also more likely during pregnancy. 

Studies are actually showing now that it’s riskier than ever.  Even those women who gain just 15 to 25 pounds of excess weight have a higher risk of Cesarean sections and obese babies in general terms than those who had gained less than 15 pounds in the whole process.  It also has been shown that obese mothers are more likely to have to stay in the maternity ward due to cesareans and other complications, and they require greater testing during pregnancy.  Likewise, blood clots are more likely to form, and otherwise you are more likely to have basic complications in general.  Obese patients at this point are advised to actually avoid gaining any weight during pregnancy while the normal woman would naturally gain about 20-25 pounds.