I fail to see how John the Baptist leaping in Elizabeth's womb correlates to the Virgin Mary having a "normal" pregnancy.
We are told that it happened at what was probably the 5-6 month mark of Elizabeth's pregnancy. In any case, we are told that Jesus was already in Mary's womb at that time.
Therefore, we know that there was some amount of gestation taking place because Mary stayed with Elizabeth for 3 months. She then returned home. It was some time after that that she gave birth to Jesus.