Have never considered this before. Can't think of a reason there should be any significance in it. What prompted the question?
A face book freind asked the question and as you I never considered it before, and did a little searching on it and came up with a very interesting view,
Why did Jesus never call Mary mother
Because He did not want us to worship her or to look at her as though she was a goddess.
Luke
11:27 And it came to pass, as he spake these things, a certain woman of the company lifted up her voice, and said unto him, Blessed [is] the womb that bare thee, and the paps which thou hast sucked.
11:28 But he said, Yea rather, blessed [are] they that hear the word of God, and keep it.
Matthew
2:46 While he yet talked to the people, behold, [his] mother and his brethren stood without, desiring to speak with him.
12:47 Then one said unto him, Behold, thy mother and thy brethren stand without, desiring to speak with thee.
12:48 But he answered and said unto him that told him, Who is my mother? and who are my brethren?
12:49 And he stretched forth his hand toward his disciples, and said, Behold my mother and my brethren!
12:50 For whosoever shall do the will of my Father which is in heaven, the same is my brother, and sister, and mother.
Catholic Answer Jesus is using all due respect and love for His mother. She plays a very important part in the economy of salvation. After all, we would not have been saved were it not for her "Fiat" at the Annunciation, when the Archangel, Gabriel, asked her to bear the Son of God, and she replied, "Fiat" - Be it done to me according to your word. She is replacing Eve, who as mother of the entire human race, gave us only sin and death. Mary, in her humble obedience, is granting to the entire human race grace and salvation. Jesus acknowledges this role for her, and gives her to all of us, through the apostle, John, as our mother. She is the "woman" who gives the world its Savior who will crush the head of Satan (Gen. 3:15). Remember that the language you are reading in the Bible is a translation of another language that is recording a culture that is over twenty centuries removed from our own. You can not color the word "woman" with the way it is used on the television in the twenty-first century and expect to understand what Jesus is saying.