Which of the following is a risk factor for placenta previa?

A risk factor for placenta previa is being older than 35 years. This is relevant because as a woman ages, various physiological and hormonal changes can occur, which may affect the placement of the placenta in relation to the cervix during pregnancy. Older maternal age can lead to a higher likelihood of certain complications, including abnormal placental implantation, which is a key feature of placenta previa.

In terms of pregnancy, advanced maternal age is associated with an increased risk of several conditions that can complicate pregnancy, including placental abnormalities. Therefore, recognizing age as a significant risk factor is essential for healthcare professionals in managing pregnancies and planning for potential complications.

The other factors listed may or may not contribute to complications in pregnancy but are not established risk factors for placenta previa in the same way that age is.