If your concern is whether or not I believe Jesus was God at conception - He was. And before then.
Saying she gave him his beginning as man, I can partially agree with (in that she didn't do it alone. Only God could have performed this miracle. He used Mary's body to do so, and she was humbled that he would choose her).
I just dislike the term mother of God, because of what it implies on the surface. Theology can be difficult to grasp at times, without using terms that need to be carefully qualified in order to be understood properly. Mother of God is not the only confusing term that is used. But it would be just as easy to call her Mother of Christ or Mother of the Son of God. Or even to a point Mother of the God-Man Jesus Christ. Mother of God implies she preexisted God and is just an innecessarily confusing term. IMHO
The Church does not draft her documents for those who don't know theology, those misinformed and uneducated folks who might misunderstand a term if they came across it. She drafts her documents for her bishops and priests, those knowing the theology and tradition of the Church. The Council of Ephesus in 431 declared Mary to be the "Mother of God" specifically in response to the Nestorian heresy, and after the doctrine of the Trinity had been hammered out in the first two councils. The Catholic clergy would in no way misinterpret "mother of God" to mean that Mary was the source of the divine nature. And as I showed above, denying that Mary is "the mother of God" logically entails one of three heresies, and therefore the Church must affirm it.
-A8
That's exactly what the Nestorians and Arians wanted to do. Those are attacks on the *deity* of Christ.
Christians are called "sons of God". See John 1:12, Rom 8:14,19; Philippians 2:15; 1 John 3:1-2. So if Mary is merely the mother of the "son of God", then that makes Christ no more divine you or me.
And to be "Christ" does not necessarily mean to be "God". So, to call Mary merely the "mother of Christ" makes it possible that Christ was a mere man.
The Council knew what they were doing. Christ's divinity was at stake. And if you cave on "mother of God", you are giving away Christ's deity.
-A8
Do read the acta of the Third Ecumenical Council. They are available on line in the Eerdmans translation.
'Christotokos' was the title Nestorius insisted on, and it was precisely because the title introduced a distinction between 'the one from the Virgin' and the Divine Logos that the Church has inisted on the title Theotokos as a guard of sound Christology.