Vaginal bleeding during pregnancy has many causes. Some causes are serious. But many aren't.

First trimester

Possible causes of vaginal bleeding during the first trimester include:

1. Ectopic pregnancy The fertilized egg implants and grows outside of the uterus, such as in a fallopian tube.
2. Implantation bleeding This happens about 10 to 14 days after conception when the fertilized egg settles into the lining of the uterus.
3. Miscarriage This is the loss of pregnancy before the 20th week.
4. Molar pregnancy Rarely, a fertilized egg grows into unusual tissue instead of a baby.
5. Conditions of the cervix or vagina. These may include a cervical infection, an inflamed cervix or growths in the cervix such as polyps. For the vagina, there may be a wound, vaginal warts or growths.

Second or third trimester

Possible causes of vaginal bleeding during the second or third trimester include:

1. Incompetent cervix Also called cervical insufficiency, this is when the cervix opens too early. It can lead to preterm birth.
2. Miscarriage This is the loss of pregnancy before the 20th week.
3. Placental abruption This is when the placenta comes away from the wall of uterus. The placenta gives nutrients and oxygen to the unborn baby, called a fetus.
4. Placenta previa This is when the placenta covers the cervix. It often causes serious bleeding during pregnancy.
5. Placenta accreta This is when the placenta grows too deep into the uterine wall.
6. Preterm labor Starting labor too early might cause light bleeding.
7. Conditions of the cervix or vagina. These may include a cervical infection, an inflamed cervix or growths in the cervix such as polyps. For the vagina, there may be a wound, vaginal warts or growths.
8. Uterine rupture. The uterus tears open along the scar line from an earlier C-section or other past surgery on the uterus. This is rare but life-threatening.

Typical vaginal bleeding near the end of pregnancy

Light bleeding, often mixed with mucus, near the end of pregnancy could be a sign that labor is starting. This vaginal discharge is pink or bloody. It's called the bloody show.