What increases my risk for placenta previa?

Placenta previa occurs when the zygote implants in the lower uterine segment. Usually the zygote implants in the fundus or upper portion of the uterus. When the zygote implants itself in the lower portion of the uterus, the placenta might grow over the cervix, causing placenta previa. While the exact cause of placenta previa is not know, there are a number of factors that increase the woman’s risk for having a placenta previa. These risk factors include:

• Previous surgery that alters the lining of the uterus (i.e. D& C, myomectomy
• Previous cesarean birth
• History of placenta previa in a previous pregnancy
• History of five or more pregnancies
• Maternal age 35 or older
• Multiple gestation pregnancy
• Smoking
• Using cocaine

Basically these risk factors include events that change the integrity of the uterine lining due to either scarring of decreased blood flow and conditions that require more surface area for placental attachment and function.

While the reasons are unclear there has been a higher incidence of placenta previa found in women of Asian descent and in women carrying male fetuses. 

Placenta previa cannot be prevented. You cannot control where your placenta positions itself or where it may shift to. There is no definitive cause for placenta previa, but it seems that there are a few factors that may have some influence on it. Whether the uterus has any scrapes or scar tissue from a c-section or other surgery seems to affect placenta placement. Also, a larger than average placenta (from carrying identical twins or other multiples) or an atypical uterus may play a role in causing placenta previa. You may be able to prevent some bleeding, though, by avoiding sexual intercourse and too much activity (through bed rest).

Placenta previa is when the placenta completely or partially covers the uterine cervix. It occurs in approximately 1/200 pregnancies and places the pregnancy at risk for bleeding, premature delivery and other comlications. The mechanism leading to a placenta previa is unknown, but there are several known risk factors for this including:

• Advanced maternal age
• Multiparity (or multiple previous deliveries)
• A history of prior abortions (spontaneous or elective) and uterine surgeries
• A previous C-Section
• A history of placenta previa in a prior pregnancy
• Multiple gestations
• Male sex
• Cocaine use
• Cigarette smoking (and there appears to be a dose-dependent relationship for this)

Placenta previa occurs when the placenta partially or completely covers the opening of the uterus (cervix). The risk for placenta previa is greater for women who:

• Are older than 35
• Have had more than one previous delivery
• Have had uterine surgery (D&C, myomectomy, etc.)
• Are carrying twins
• Have had a previous cesarean section
• Have had a previous placenta previa