In recent years I've noticed a trend towards referring to Christ's "virgin conception," rather than His "virgin birth." I headed the same way, myself.
My preference for the former expression grew out of a desire to emphasize the Biblical affirmation that life does not begin at birth, but at conception. So Christ's human life did not begin at birth, but at His conception.
But as I was recently preparing a sermon on Matthew 1:18-25, something occurred to me. It can be put very simply.
Theoretically, one could have a virgin conception, but not a virgin birth.
However, if there is a virgin birth, there was, by necessity, a virgin conception.
And since the Bible equally insists on both (Matthew 1:18, 20, 23, 25), the latter phrase is the better one, inasmuch as it alone necessarily affirms both truths.
(If my reasoning is unclear to you, perhaps your mother could fill in the details.)