While bleeding during pregnancy in the first trimester is quite common and usually not cause for concern, most of the cases later in pregnancy are far more rare, but also often less benign unfortunately.
You may also find these posts on early bleeding during pregnancy that may be mistaken for a period or bleeding or spotting during the first trimester helpful. Some reasons for light bleeding in the first trimester covered in the above linked post also apply later in pregnancy such as cervical changes or damage, sub chronic hematoma, and infection.
Causes of bleeding during pregnancy:
Placenta abruption: Placenta abruption occurs when the placenta partially or completely separates from the uterine wall before birth. This can deprive your baby of nutrients and oxygen. Minor abruptions can be managed with rest.
Uterine rupture: Uterine rupture is most common in women who have previously had a c-section and is rare even in that case. Usually during early labor contractions, the uterine wall tears causing uterine rupture. Uterine rupture is life threatening to both mother and child and requires emergency c-section.
Placenta Previa: Placenta previa occurs when the placenta partially or completely covers the cervix (the opening from your womb to the vaginal canal.) Depending on the severity of placenta previa, treatment may range from bed rest at home without physical exertion or sex to emergency c-section.
Vasa previa: Note that this condition is quite rare occurring in 1 in every 2000 pregnancies, but is seen more in those who also have placenta previa. Vasa previa occurs when the blood vessels in the umbilical cord block the cervix. It is harmless during pregnancy, but can prove fatal to your child during delivery as the rupture of these vessels will cause blood loss from the baby.
Incompetent cervix: Incompetent cervix occurs when the cervix is weak and attempts to open or does open before the end of your pregnancy. This condition is present throughout pregnancy, but isn’t typically symptomatic causing bleeding during pregnancy until the baby becomes large enough to begin placing weight on the cervix. It is one of the most common causes of second trimester losses. You may notice increased pressure, as if your baby has dropped into the pelvis, a change in discharge prior to spotting or bleeding, back pain, or contractions. An incompetent cervix can be treated by stitching the cervix closed if caught before preterm labor has occurred.
Miscarriage or Premature labor: Before 20 weeks an attempted loss or loss is still referred to as a threatened miscarriage or miscarriage, after 20 weeks it is referred to as premature labor. All of the above mentioned causes of bleeding during pregnancy can also be a cause of miscarriage or preterm labor. Certain infections, abdominal trauma, and chromosomal abnormalities can also be to blame, but in other cases no cause is known. Take heart, however, in knowing the current rate of miscarriage after a heart beat is seen at 8 weeks is a mere 1 percent.
As mentioned in the other installments of this series on bleeding during pregnancy, any bleeding, no matter how slight, should be reported to your doctor right away. Light bleeding during pregnancy is very likely no cause for concern, heavy bleeding can be more serious, but either way, better safe than sorry.