My dearest daughter since your pregnancy prevents you from making your usual long mental prayer, make your prayer short and fervent. Make up for the loss by frequently lifting your heart up to God; often read from some good spiritual book, but only a little at a time; when you go for a walk, often turn your thoughts to God; pray often and briefly; offer your listlessness and weariness to our crucified Lord. After your delivery, quietly resume your usual devotions, and discipline yourself to use the subject matter presented in some spiritual book, so that when it is time to go to prayer you are not at a loss, like the person who, when it is time for dinner, has nothing ready. If sometimes you don�t have a book to turn to, meditate on a mystery rich in meaning, like the death and passion [of our Lord], or whatever first comes to your mind.
from a letter of spiritual direction, found in the book Francis De Sales, Jane De Chantal: Letters of Spiritual Direction
thanks to Jennifer at Conversion Diary for pointing me toward this book.