Placenta previa is a condition in which the placenta lies low in the uterus and partially or completely covers the cervix. The cervix is the opening of the uterus that allows the baby to pass through during delivery. If the placenta blocks this opening, it can interfere with a safe vaginal birth and may cause complications, especially if bleeding occurs.
There are different types of placenta previa:
- Complete previa: The placenta fully covers the cervix.
- Partial previa: The placenta covers part of the cervix.
- Marginal previa: The placenta is near the edge of the cervix but does not cover it.
- Low-lying placenta: The placenta is implanted in the lower part of the uterus, close to but not touching the cervix.
In many cases, placenta previa detected early in pregnancy resolves on its own as the uterus grows and the placenta moves upward. When the condition persists later into the pregnancy, careful monitoring is essential.
What Causes Placenta Previa?
While the exact cause isn’t always clear, several factors may increase your risk of developing placenta previa:
- Previous cesarean delivery
- Previous placenta previa
- Carrying multiples (twins or more)
- Uterine surgery or scarring (including dilation and curettage)
- Smoking during pregnancy
- Advanced maternal age (35 or older)
It’s important to note that placenta previa is not caused by anything you did or didn’t do. It simply means the placenta implanted in a position that now requires additional observation and planning.
How Is Placenta Previa Diagnosed?
Placenta previa is most commonly diagnosed during a routine second-trimester ultrasound, usually around 18 to 20 weeks. If the ultrasound shows the placenta is covering or near the cervix, your provider may schedule additional ultrasounds in the coming weeks to monitor whether the placenta moves upward as the uterus expands.
In many cases, what appears as previa at 20 weeks becomes a non-issue later in pregnancy. However, if the placenta still covers the cervix in the third trimester, it is considered a persistent placenta previa and may require specific care adjustments.
