Final answer:
A pregnant woman is at increased risk for vasa previa if she has a history of previous vasa previa, is carrying multiple fetuses, or if she has a placenta previa, where the placenta partially or completely covers the cervix.
Step-by-step explanation:
A pregnant woman may be at increased risk for vasa previa if she has a history of previous vasa previa, she is carrying multiple fetuses, or she has a placenta that partially or completely covers the cervix (placenta previa). Vasa previa is a condition where fetal blood vessels cross or run near the internal os of the cervix beneath the fetal presenting part. If the blood vessels are ruptured, it can result in severe fetal hemorrhage.
Placenta previa occurs when an embryo implants close to the cervix and, as the fetus grows, the placenta can partially or completely cover the cervix. This condition is the leading cause of antepartum hemorrhage. Increased risks are associated with multiple pregnancies, where the development of the placenta might be affected, and a previous history of vasa previa, which may suggest a recurring issue with placental positioning. Other factors like low BMI and history of smoking are also risk factors for pregnancy complications, but they are not specifically linked to increased risk for vasa previa as per the provided context.