Placenta Previa and When It's a Cause for Concern
There are a few different causes for bleeding late in the pregnancy. You might be going into labor. In that case, you may experience crampy abdominal pain (like menstrual cramps or even stronger contractions) and have a bloody, mucous-like discharge known as bloody show. Another cause is where the placenta separates prematurely, called a placental abruption. This could be very mild or heavy, and is usually associated with intense abdominal pain and contractions. Finally, placenta previa, where a portion of the placenta covers the internal part of the cervix, can be a cause of bleeding.
It is not uncommon for placenta previa to be found on a routine ultrasound at the 20-week anatomy scan (up to 6%), but most (90%) of the time, the placenta moves out of the way. However, sometimes it can persist, and be a cause of bleeding and even preterm delivery.
Placenta previa should be considered in any woman who is past 20 weeks and has painless vaginal bleeding, although some women may experience contractions as well as bleeding. Some risk factors include a history of prior placenta previa, carrying twins or more, prior delivery by cesarean section, already having some children, being over age 35, and having had treatment for infertility.
Bleeding may occur when the lower segment of the uterus or cervix changes and cause some detachment of the placenta. Often this is precipitated by a vaginal exam or intercourse.
About one-third of women with placenta previa have bleeding before 30 weeks, with a greater chance of preterm delivery. Another one-third of women have bleeding for the first time between 30–36 weeks, while the rest may not bleed until after 36 weeks.
If placenta previa persists into the latter part of the third trimester, a cesarean delivery is scheduled at about 36–37 weeks (unless multiple episodes of bleeding have occurred).
Don’t forget that placenta previa at 20 weeks is not unusual, and most do not persist. However, if you experience any bleeding during your pregnancy, be sure to speak with your healthcare provider right away.