Hi, It is quite common for bowels to get constipated during pregnancy. You should take plenty of fluids and fiber diet for easy stool. Miralax can be used during pregnancy only if clearly indicated, in fact, any laxative or purgative is not advisable during pregnancy. Intake of milk, figs, prunes, carrot juice, regular bowel training, walking, pelvic floor muscle exercise and intake of the herb isabgol are some of the methods of treating constipation in pregnancy. Prenatal vitamins may cause constipation but they need not be stopped if the other methods mentioned are followed. Please get further advice from your doctor. Good luck.