I say, and with God's success: There is no sin on one who breaks their fast after starting the fast of Dhul-Hijjah; because it is a voluntary fast, and there is no sin for one who breaks their fast after fasting in a voluntary manner. However, they must make up this day regardless of whether they have an excuse, such as being pregnant, or without an excuse; because it is obligatory on the soul after starting. It is disliked to break the fast if there is no excuse, and if there is an excuse, the dislike is removed. God knows best.