Multiple. Placental abruption, placenta previa , local lesions and unidentified cause, are the commonest reason behind bleeding in the third trimester.
Variety of causes. First of all consider calling your OB about bleeding while pregnant. The most common reason is a recent office exam or sex. Concerning reasons include preterm labor, abruption, placenta previa and vasa previa. Its always a good idea to call your OB and discuss bleeding and i would do it as soon as possible.
Needs evaluation. Bleeding during pregnancy should always be investigated. In the third trimester, causes may be non harmful cervical changes to more concerning placental issues. Their effect on the baby really depends entirely in the cause. If it is noted after sex, and it is light, it may just be due to cervical irritation. That is ususally ok. Heavier bleeding requires an ultrasound and/or blood tests. Visit ob. Read more...