Shapeshifting during very early pregnancy would be a risk, but not a 100% guarantee of problems. As the pregnancy progresses and the fetus grows more complex, however, the strain that the magic and transformation placed on it would create insurmountable odds of complication or miscarriage. After the 12-week mark, the mother runs significant risk of laying an egg. Literally.

If Pel does any research into the subject once she realizes she's expecting, she'd be able to uncover some vague written accounts of Dalish or "barbarian" shapeshifters whose pregnancies results in stillbirths, severe birth defects, etc., to warn her off of continuing to shapeshift.