From Mulieris Dignitatem (On the Dignity and Vocation of Women) by John Paul II:
Motherhood implies from the beginning a special openness to the new person: and this is precisely the woman’s “part”. In this openness, in conceiving and giving birth to a child, the woman “discovers herself through a sincere gift of self”. The gift of interior readiness to accept the child and bring it into the world is linked to the marriage union, which — as mentioned earlier — should constitute a special moment in the mutual self-giving both by the woman and the man.