Hi & Welcome. Yes, it may cause harmful effects to your unborn baby. Primolut-N is a Progesterone (Norethisterone) which is mainly used to treat heavy irregular menstrual bleeding or delayed periods. It should be stopped once the pregnancy is confirmed by the transvaginal ultrasound. It is known to hinder endometrial changes and implantation of the embryo resulting in fetal deformities in case of pregnancy or suspected pregnancy. If taken in high dose it may also cause virilization of female unborn babies especially after 45 days of pregnancy. But there s nothing to worry about it since you have used it for short period of time (4 weeks), the chances of serious consequences are less. However, it is necessary to undergo periodic regular ultrasound scans to monitor your baby if you want to continue the pregnancy. I advise you to consult gynecologist at the earliest and start taking iron & folic acid and multivitamin capsules. Hope this answers your query. A feedback is appreciated.