Does Luke 1:34 suggest that Mary took a vow of perpetual virginity?

Roman Catholics and other advocates of Mary's perpetual virginity often claim that Luke 1:34 implies that Mary had taken a vow of perpetual virginity. Why else would she ask Gabriel how she was to conceive? These same Catholics (and others) often cite the second-century apocryphal work The Protevangelium Of James to support their view that Mary was a perpetual virgin. Go here and do a Ctrl F search for "apocryphal document" to read about some of the problems with that sort of appeal to the document. The Protevangelium has Mary needing to be corrected by Gabriel about becoming pregnant the same way other women do (11). It doesn't seem that the author of the Protevangelium interpreted Luke 1:34 the way these modern Catholics interpret the passage. Here are some other observations on Luke 1:34, which I wrote in correspondence with a friend on Facebook last year:

One factor to keep in mind is that Mary wouldn't have to think a pregnancy in the near future was likely in order to take it seriously as a possibility. She could have been asking Gabriel for confirmation that the pregnancy would happen in the usual manner without thinking it was probable that anything other than the normal scenario would occur. All she would need is some reason for thinking that a potential unusual scenario should be taken seriously as a possibility. And she had some reason for that.

For one thing, Gabriel was appearing to her long before the wedding. The timing of Gabriel's visit may have raised a question in Mary's mind about why she was receiving the annunciation so early if the pregnancy wasn't to occur until a few months or more later. And there may have been one or more other nonverbal factors involved that raised doubts in her mind about conceiving in a normal way (e.g., an intuition, maybe even a Divinely-inspired one; something in Gabriel's original language that suggested imminency, even though that isn't discernable in the Greek of what Luke recorded). There's also a verbal factor we should take into account. Notice the reference to how "you will conceive in your womb" in verse 31, which is an unusual way to refer to a pregnancy. That may have raised a question in Mary's mind, even though the work of the Holy Spirit hadn't been discussed yet. Since that unusual language was being used to describe the conception, might it occur in an unusual way?

In the larger context, there's a pattern of people not fully understanding what's going on (Luke 1:18, 1:59-63, etc.), including Mary (2:35, 2:48-50). In the more immediate context, Mary's response is contrasted to what Gabriel said. We're told that she was "very perplexed" and "kept pondering" Gabriel's greeting. He then tells her to not be afraid, which may mean that she was being corrected in some manner. If she kept pondering in response to Gabriel's greeting, there's a good chance she also did so in response to what he went on to say. If so, her question in verse 34 might be shaped by her thinking of multiple ways Gabriel's comments could be interpreted. Luke goes out of his way in verse 29 to tell us how much Mary was perplexed and pondering, so the text explicitly encourages us to think along those lines.

If you're interested, you can read Eric Svendsen's comments on the perpetual virginity vow issue on page 104 and following in his doctoral thesis on Mary at:

https://repository.nwu.ac.za/handle/10394/10309