[Sherman Logan]

If Joseph and Mary were married—and they were—and they were planning the normal course, Mary would have known full and well how she could and would have a baby. As St. Augustine said, the question reveals the fact that this was not just your average, ordinary marriage. They were not planning to consummate their union.

Neither the Bible nor Jewish custom of the time had anything at all in them about a celibate marriage. Would have been viewed as weird if not obscene.

The Bible itself also says nothing about the couple having for some obscure reason planned such a "union." In fact, there is nothing at all in the text to indicate they planned anything other than a normal Jewish marriage till first Joseph and then Mary were visited by angelic messengers.

[GeronL]

I don’t remember anything in the Bible about them not having a normal marriage.