The book "Them Good Old Wild Greens: Borderline Starvation was a Way of Life in the 1930's," contains this quotation from a Dr. John Clifford, "Thousands of individuals died during the great depression of the 1930's because of the lack of nourishing food. This weakened the body's resistance, causing it to be unable to fight off sicknesses and diseases. The cause of these deaths was seldom listed as starvation." The book was compiled by a Mr. James T. Carrier, copyright 1998, E.U.L.A. Publishers, 907 N. Noble St., Greenfield, Indiana 46140. No reference is given for the Clifford quote, although it is dated to 1980.
Carrier's book tells how he and other boys approximately age 10 and older were sent to live off the land each summer during the depression to reduce their family's food shortage. He also describes families gathering wild greens each spring for nourishment.
It would seem this lack of nourishment would produce the type of birth defects you describe. And, if Dr. Clifford is right, if family's would not attribute death to starvation, they would no doubt not attribute birth defects to poverty. Would state health departments of that day have kept records of the birth defects. It seems some record would have been kept if it had been an epidemic--even if the defects were not attributed to malnutrition.

Oh cool. Does your novel also take place in some parts on the planet Zebulon in 2069? :D