Making the Diagnosis
The condition may be diagnosed by an ultrasound showing the position of the placenta. If it is detected late in the first or second trimester, often the placenta's location will shift as the uterus enlarges. This can be followed by ultrasound. Some women may even remain undiagnosed until delivery, especially in cases of marginal placenta previa. Painless bleeding from the vagina during the third trimester of pregnancy may also indicate the condition.
In many cases, a diagnosis of placenta previa in the early weeks (usually before week 20) may correct itself as the pregnancy progresses. In other cases, placenta previa may be missed if the placenta is located behind the baby's head.
Digital (using the fingers) examination of the vagina and the cervix is avoided in cases of placenta previa, as this could cause the placenta to tear and lead to heavy bleeding.
In addition to painless vaginal bleeding, other signs that your doctor may look for to confirm a diagnosis of placenta previa include:
- a soft and relaxed uterus
- the fetus is positioned either horizontally in the uterus or at a sideways angle (in 15% of the cases)
- abdominal ultrasound during the second trimester showing the low placement of the placenta
- low lying placenta revealed by transvaginal or transperineal ultrasound