It is said that women should not work during Lunar Eclipse or Chandra Grahan. It is said that doing so effects the physical health of the baby.
Is there any mention of this in the scriptures, or any specific reason behind this ritual?
It seems that the thoughts during the sexual union for conceiving a child & later during the pregnancy, are important for the mental & physical healths of that child.
From Garbha Upanishada:
Action corresponds to the mental state (of the actor). Hence the child (born) takes after (the thought of) the parents. From parents with minds full of anxieties (at the time of union) are born the blind, the lame, the hunchback, the dwarf, and the limbless. (From impregnation) during the eclipses of the sun and the moon, children are born with defective limbs. Increase or decrease, similarities or dissimilarities of bodies arise (in children) through the influence of time, place, action, ḍravya (substance), and enjoyment. From a well-conducted intercourse (or union), the child being born with the form of the father possesses, his qualities, just as the image in a glass reflects truly the original.
Hence the state of "impregnation" as described above, also could be extended to the state of "pregnancy".