Opening the Ark in the Ninth Month

Peace and blessing! What is the source for the custom of the husband to open the Holy Ark when his wife enters her ninth month of pregnancy? And is there a point in opening the Ark throughout the ninth month or just once at the beginning of the month? (If possible, please send me the answer by email as well because it seems that NetFree will not allow me to open such a question on the site)

Shalom!
The first source I saw is the Chida in his book 'Moreh BeEtzba', 'And the custom of the city is that when his wife enters her ninth month of pregnancy, he (the husband) is careful to perform the mitzvah of opening the Holy Arc that month and it is a beautiful custom and it has a basis in the path of truth (kabbalistic teachings)'. In these words it seems to be implied that there is a point in doing this throughout the month and not just at the beginning of the month.
However, in another book, LeDavid Emet, the Chida cites this custom phrasing it differently: 'It is customary in some communities that when his wife enters her ninth month of pregnancy, the husband buys the mitzvah of opening the Holy Arc in that month, and it is a beautiful custom and it has a basis in the path of truth (in Kabbala)'. And from his wording there, it seems that the custom is only to do this at the beginning of the month and not throughout the month.

Moreh BeEtzba, section 3, §90; LeDavid Emet, section 2, §3