Placenta previa is a complication of pregnancy where a woman's placenta attaches to the uterus so low that it borders or covers the cervix. The placenta is your baby's lifeline - it gives nutrients and oxygen, and takes waste from your baby. Placenta previa is the number one cause of bleeding during the latter half of pregnancy, and is a potentially serious complication. It can prevent a normal, vaginal delivery by blocking the cervix, or can detach during cervical dilation, causing heavy bleeding.

Fortunately, placenta previa often resolves itself as the placenta slowly moves upward during the course of the pregnancy - only 10% of women diagnosed with low lying placenta or placenta previa actually still have the complication by delivery.

There are four different levels of placenta previa: low lying placenta, marginal placenta previa, partial placenta previa, and total placenta previa. Low lying placenta is diagnosed if the placenta is lower than normal, no less than 2 cm. from the cervix. Marginal placenta previa occurs when the placenta is close to the cervix - within 2cm. The cervix is partial covered with partial placenta previa, and completely blocked with total placenta previa.

There are several potential causes and risk factors for developing placenta previa. If you have a larger than usual placenta due to multiples or other factors, it may implant too close to the cervix. If your uterus is shaped abnormally or you have scarring of the uterus, you may have it as well. Other risk factors include:

• Older maternal age - over 35
• Previous placenta previa
• Multiples
• Previous pregnancies, or c-section
• Surgery on uterus
• Smoking

Routine prenatal care will typically reveal placenta previa by 20 weeks. If you are diagnosed with low lying placenta, you typically have no special precautions you need to take since it usually resolves itself. Depending on the severity of your placenta previa, your doctor may recommend bed rest, no sexual intercourse and possibly a planned cesarean delivery. Your doctor will also most likely perform a follow up ultrasound to determine if the placenta previa has resolved itself, or where it is lying during your third trimester.

Complications include heavy bleeding, placenta accreta, when the placenta doesn't detach after delivery, and premature delivery. If you experience bleeding during the second half of your pregnancy - especially if it is bright red and heavy - be sure to contact your doctor immediately.