Woe to the one who says to his father, "What will you engender?" or to a woman, "What will you writhe over in labor?" [Isaiah 45:10]
John Oswalt (Isaiah 40-66: New International Commentary on the Old Testament) comments on the last part of the above verse as follows:
Commentators have questioned why woman is used in the second bicolon instead of the expected parallel, "mother." The solutions offered have generally been inconclusive, but this may be another example of the Bible's careful refusal to give even the appearance of labeling God as Mother. Once that equation is permitted to stand it becomes all but impossible to maintain the doctrine of transcendence on which all biblical revelation stands or falls. This is so for two reasons: (1) because there is a physical continuity between mother and child, and (2) because of the total association of mother goddesses in the ancient Near East with fertility and reproduction.
I think Oswalt is right that the biblical authors are reluctant to make explicit statements about God as mother. This is worth contrasting with using clear feminine imagery about God, which they certainly do, albeit not as often as they use masculine imagery. But they don't speak of God as mother.
I'm curious what it means if Oswalt is right about the reasons for avoiding such a conclusion. Oswalt's reasoning seems to me to be friendly to some feminist views, in at least one respect. The reason for not using explicit mother language is at least in part culturally-conditioned, since his second explanation involves something true only of the immediately surrounding cultures.
But it does also involve something universal, even if it is contingent. The close physical continuity between mother and child is not culturally-relative. Only in science fiction scenarios with artificial wombs can you minimize that continuity, and even then it doesn't remove it entirely, since an egg has a little more connection with a mother than a sperm cell does with a father, and the fertilized egg has more connection with the egg than the sperm cell that fertilized it.
Yet both explanations do not rely on any sense of God being male, and thus the usual view that God is neither male nor female but has chosen male language to be more revealing of his nature seems to make sense on Oswalt's account.