I think the article was generalizing. Much of birthweight is genetic,and not all low birth weight or preemies are at a disadvantage (both of my older brothers were premature and low weight and spent time in an incubator-and both are sucessful judges,and one of them is a law professor as well, and they came from an extremely poor immigrant family).It also doesn't really depend on the size of the mother. The largest baby I have ever seen was over 14 pounds and delivered by a four foot ten Vietnamese woman in her early twenties who gained 17 pounds during her pregnancy. I was almost 9 pounds,my mom only gained 8 pounds while pregnant. Unless a mother is an alcoholic,ill or on drugs,a baby will get what it needs. Certain lifestyles can cause prematurity. On the other hand,I have taken care of mothers who went full term and found out they were pregnant less then 2 weeks before delivery and had perfect infants.One woman I worked with,age 26,overweight to start and gaining too much during her pregnancy had a large Down syndrome infant. She had excellent prenatal care,but she did have gestational diabetes-and she had a large baby.
I do think (as a nurse and a scientist) that there are too many factors-beyond environment and heredity-to generalize.

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Russian/Chinese, from planet NARS, age 45. "If its pink and sparkley I will shoot it...."