Menstruation is one of the events of the menstrual cycle : It consists of the shedding of the inner lining of the uterus (the endometrium) through the vagina, accompanied by bleeding. Throughout each menstrual cycle, the sex hormones estrogen and progesterone prepare the uterine lining for a possible pregnancy. If fertilization and implantation of an embryo in the uterus do not occur, pregnancy does not happen and the uterine lining is no longer needed. The lining is then shed during menstruation, and a new menstrual cycle begins. If fertilization and implantation do occur, the endometrium is not shed: It is needed for the development of the embryo and the continuation of the pregnancy. Menstrual cycles stop for the duration of the pregnancy. Therefore, a woman cannot be pregnant and have a true menstrual period at the same time. For this reason, menstruation is different from any vaginal bleeding or blood loss that occurs during pregnancy , and such bleeding does not always mean that something is wrong. Is it possible to have menstruation even at the very beginning of pregnancy? No. If a woman thinks she may be pregnant (but the pregnancy has not yet been confirmed) and experiences vaginal bleeding: Either it is a true menstrual period and there is no pregnancy; Or, if a pregnancy exists, the bleeding has another cause. Is vaginal bleeding during pregnancy serious? Vaginal bleeding during pregnancy can have many causes. Depending on the cause, it may be harmless and resolve on its own, or it may indicate a problem requiring urgent medical attention. For this reason, any pregnant woman who experiences vaginal bleeding should seek medical advice. What causes bleeding during pregnancy? Vaginal bleeding is more common during early pregnancy. The most common causes are benign, and the bleeding often resolves on its own. Small amounts of bleeding during the first weeks of pregnancy are sometimes associated with implantation of the embryo into the endometrium: They occur around the time when a menstrual period would otherwise be expected; They usually appear as a light reddish-brown discharge and last only a short time; They do not occur in all pregnancies. Minor bleeding caused by small injuries after sexual intercourse or gynecological examinations is also common because the cervix and uterine area become more sensitive and have an increased blood supply during pregnancy. In some cases, no specific cause can be identified, particularly when the bleeding is light and occurs only once. Other possible causes of vaginal bleeding during pregnancy, which may indicate more serious conditions, include: Miscarriage; Ectopic pregnancy, meaning a pregnancy that develops outside its normal location within the uterus; Molar pregnancy (hydatidiform mole), in which there is no viable embryo and abnormal placental tissue develops instead; Placental problems, such as placenta previa or placental abruption, which usually occur later in pregnancy; Infections. When should medical care be sought? Any pregnant woman who experiences vaginal bleeding should seek medical advice. Medical attention is particularly important and urgent when the bleeding is: Persistent; Heavy; Accompanied by blood clots or tissue; Accompanied by severe and persistent abdominal pain; Accompanied by dizziness or fainting; Associated with a general feeling of being unwell. In short There is no true menstrual period during pregnancy. Some women may experience vaginal bleeding, most often light bleeding in early pregnancy. In most cases, this bleeding is not serious. However, it is important to speak with a healthcare professional so that the cause can be identified and treatment provided if necessary. Author: Claudia Guerra (gynecologist) Meet the Gynecology-Obstetrics team at Hospital da Luz and schedule your appointment. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
