John Lightfoot on Luke 1:24

[She hid herself five months.] "She hid herself five months, saying, Thus hath the Lord dealt with me, in the days wherein he looked on me, to take away my reproach among men."

She was big with child, it is plain, because God had looked on her, and taken away her reproach among men. She hid herself, because the Lord had dealt so with her, till he had taken away her reproach; giving her so remarkable a son, one who was to be so strict a Nazarite, and so famous a prophet. Lest therefore she should any way defile herself by going up and down, and thereby contract any uncleanness upon the Nazarite in her womb, she withdraws, and sequesters herself from all common conversation. Consult Judges 13:4.

There were several amongst the Jews that were wont to take upon them the sect of the Nazarites by their own voluntary vow. [Three hundred at once in the days of Jannaeus the king came together to Simeon Ben Shetah.] But there were but two only set apart by divine appointment, Samson and the Baptist: whom the same divine appointment, designing to preserve untouched from all kind of pollution even in their mothers' wombs, directed that the mothers themselves should keep themselves as distant as might be from all manner of defilement whatsoever. Elizabeth obeys; and for the whole time wherein she bore the child within her, she hid herself, for her more effectually avoiding all kind of uncleannesses; although it is true we have the mention but of five months, by reason of the story of the sixth month, which was to be immediately related, verse 26.