For Expecting Moms: to Yo-Yo Is a No-no
A study in Ireland has determined that weight fluctuation in either direction can endanger pregnancies. In this case, the doctors acknowledge that the conflicting messages sent forth by the media and the health industry are damaging and confusing people. Clearly, aggressive dieting or complete disregard for food intake and exercise does some harsh things to the body, and a child conceived in that particular internal environment will suffer for it. That makes sense.
This does not give an indication whether an overweight mother conceiving who maintains the same weight between pregnancies would be harmful or helpful to the baby.