Normally, your uterus does not compress your colon. When a woman gets pregnant, her uterusÂ expands. When this happens, pressure is constantly applied to your large intestine and rectum.Â This impedes the normal contraction of that part of your digestive tract. This results to constipation, wherein you cannot defecate. This is accompanied by constant urination because the expanded uterus also compresses the urinary bladder. When youâ€™re pregnant and you urinate a lot, very little water is reabsorbed in your colon. This event also contributes in your constipation as well.