Symptoms

Symptoms of placenta previa include one or both of the following:

• Sudden, painless vaginal bleeding that ranges from slight to heavy. The blood is often bright red. Bleeding can occur as early as the 20th week of pregnancy but is most common during the third trimester.
• Symptoms of preterm labor, such as regular, menstrual-like cramps, or a feeling of pressure in your lower abdomen. The bleeding from placenta previa can cause the uterus to contract.

Bleeding from placenta previa may taper off and even stop for a while. But it nearly always starts again days or weeks later.

Some women with placenta previa do not have any symptoms. In this case, placenta previa may only be diagnosed by an ultrasound done for other reasons.

Exams and Tests

An ultrasound test is used to diagnose a low-lying placenta or placenta previa, in which the placenta partially or fully covers the cervix. But ultrasound does not always provide a clear picture of the placenta's location.

Unless an immediate cesarean delivery is planned, a pelvic (vaginal) examination is not done because of the risk of further injuring the placenta, causing heavier bleeding.

Electronic fetal heart monitoring is used to check the fetus's condition.

When an early delivery is needed, an amniocentesis may be done. It is used to find out whether the fetus's lungs are ready to breathe well after birth. For an amniocentesis, a needle is inserted into the mother's belly to take a small sample of amniotic fluid from inside the uterus. This fluid is made by the fetus's lungs. A lab test of the fluid can test for signs that the lungs are well developed.