Hallow Dear, During masturbation, all the muscles contract the same way they are contracting during intercourse; in fact many times they contract more forcefully. Due to the contractions of the abdominal muscles, you are getting the tightness and soreness in the abdomen. This should not cause any problem to your baby. I would request you to be rather gentle during masturbation. Instead of stimulating whole vulva and perineum, if you concentrate and restrict only to clitoral and labia minora stimulation, you may be successful in limiting vigorous movements of the whole body, particularly abdomen during masturbation. I would advise you to avoid pillow or stuffed animal as a toy for masturbation since their cleanliness cannot be guaranteed. You should not take any chance of introducing any infection in and around vagina. It may prove to be risky for your pregnancy. A clean washed hand or fingers can serve the purpose. Please do not use any latex rubber (condom or gloves are made of it) since its touch to the urinary opening (which is just below the clitoris) causes inflammation of urinary passage. I hope this helps you. The take home message is Be gentle; be clean . Dr. Nishikant