In response to your letter of the 23rd of Iyar, in which you ask my advice regarding your brother having male children, and healthy children:

.... You should also find out from your brother whether his wife is careful to observe Kisui HaRosh. For the Zoharic statement is known, that a woman's observance of tznius and especially Kisui HaRosh brings about "blessings of above and blessings of below, with wealth, with children and grandchildren, etc."

Excerpt from Igros Kodesh, Vol. VII, p. 259