August 31, 2026 Placenta previa is a pregnancy complication . It occurs when the placenta implants in the lower part of the uterus and may lie close to, or covering all or part of the internal opening of the cervix. The cervix is the passage through which the baby leaves the uterus during a vaginal birth. When the placenta covers this passage, vaginal delivery is not possible. In any pregnancy, placenta previa increases the risk of preterm birth and cesarean section. When the placenta reaches the internal opening of the cervix, delivery must be performed by cesarean section. In many women, a placenta that is initially low-lying tends to move away from the cervix as the pregnancy progresses, meaning that a cesarean section may not be necessary. What is the placenta and which pregnant women are at greater risk? The placenta is a temporary organ that develops during pregnancy . It attaches to the wall of the uterus, usually in its upper region, and is connected to the baby through the umbilical cord. Through the placenta, oxygen and nutrients are supplied to the baby, and waste products are removed. Placenta previa , which is the implantation of the placenta in the lower part of the uterus, close to or covering all or part of the internal opening of the cervix, can occur in any pregnancy . Its cause is unknown, but the risk is higher in women who: Become pregnant at an advanced maternal age, especially after 35 years of age; Have a previous history of placenta previa; Have had multiple pregnancies; Have had previous cesarean sections, particularly more than one; Have undergone uterine surgery; Conceived through medically assisted reproduction techniques; Smoke; Use certain illicit substances. Placenta previa can cause severe bleeding during pregnancy, delivery, and the postpartum period. Diagnosis of placenta previa The diagnosis of placenta previa is made by ultrasound following complaints of vaginal bleeding or during a routine ultrasound examination. The main symptom that may be associated with placenta previa is painless vaginal bleeding with bright red blood, usually occurring during the second half of pregnancy . It may not be possible to identify a trigger for this bleeding. Bleeding occurs because uterine growth and changes in the cervix can cause small separations of the placenta from the uterine wall, resulting in bleeding. The second-trimester ultrasound (performed at 20-22 weeks) may raise suspicion of placenta previa. In such cases, additional ultrasound examinations are usually recommended, beyond the routine monitoring scans of a normal pregnancy, to determine whether the condition resolves on its own as the pregnancy progresses, which often happens. In addition to more frequent ultrasounds and depending on the location of the placenta and whether bleeding episodes occur, the doctor may recommend certain restrictions, such as avoiding strenuous physical exertion, vigorous exercise, or sexual intercourse. If, close to the expected delivery date, the placenta still covers the cervix, the baby will need to be delivered by cesarean section . Warning signs A pregnant woman, whether or not placenta previa has been diagnosed , should immediately contact her doctor or go to a hospital obstetric emergency department if she experiences: Any vaginal bleeding during the second or third trimester of pregnancy; Contractions; Reduced fetal movements; Dizziness, weakness, or a feeling of faintness associated with blood loss. 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. English translation generated with AI and reviewed by the editorial team.
