What bleeding during pregnancy means and when it's serious

• Approximately one-fourth of women will experience bleeding during the first trimester of pregnancy.
• Some causes of bleeding during pregnancy are harmless, such as implantation bleeding.
• Heavy bleeding may be a sign of complications, as it can indicate a miscarriage or ectopic pregnancy.

There are many reasons women bleed during pregnancy. Some causes are harmless, while others are serious. The cause and severity of the condition will vary depending on whether bleeding occurs in the first, second, or third trimester.

About one-fourth of women will experience bleeding during their first trimester or the first three months of pregnancy. Approximately one in 10 women will experience bleeding during the third trimester.

"The seriousness is all dependent on the reason behind the bleeding," says Julie Lamppa, APRN, CNM, midwife at the Mayo Clinic. "It can be completely benign, or it could be something that could potentially threaten the pregnancy. It's important your provider knows the full situation."

Learn more about the potential causes of bleeding during pregnancy and why it is important to seek treatment.

Causes of bleeding during pregnancy

Though it depends on each individual situation, bleeding after mid-pregnancy is associated with increased risk to both mother and fetus. The seriousness is also determined by the heaviness and duration of bleeding, Lamppa says.

These are the most common causes of bleeding during pregnancy:

Bleeding during the first trimester

• Implantation bleeding: This typically occurs 10 to 14 days after conception and comes in light spotting that lasts one to two days. This is considered normal and usually isn't a cause for worry.
• Early miscarriage: Miscarriage occurs in 15% to 25% of pregnancies. Depending on how early it occurs, bleeding can be heavy and last up to two weeks.
• Ectopic pregnancy: This happens when the fertilized egg implants and grows outside the uterus, such as in a fallopian tube. If it is not detected early enough, severe bleeding may occur and result in dizziness and fainting. An ectopic pregnancy occurs in nearly 20 out of 1,000 pregnancies in North America, and it is a leading cause of maternal death in the first trimester.
• Molar pregnancy: About one in every 1,000 pregnancies is diagnosed as a molar pregnancy, which is an overgrowth of placental cells that can cause mild to heavy bleeding, the passage of cysts, nausea, and vomiting. Because bleeding is a high risk in molar pregnancies, Lamppa says doctors will often perform a dilation and curettage procedure (D&C) to remove the fetal tissue.
• Subchorionic hemorrhage: This is characterized by the bleeding of a membrane surrounding the embryo. Though it often goes away on its own with no permanent damage, a doctor should still be consulted. If the area of bleeding expands, it can sometimes lead to miscarriage.
• Inflammation or infection of cervix: Also known as cervicitis, this condition can be caused by infection or irritation to the cervix, which may lead to bleeding, particularly after intercourse. The severity and the specific cause of the condition range from STIs to pelvic inflammatory disease. If due to an STI, cervicitis carries a risk of miscarriage or premature labor.

Bleeding during the second and third trimesters

• Incompetent cervix: This is a cervical weakness that can lead to preterm birth or pregnancy loss. It can cause light bleeding, along with pelvic pressure and cramps. The condition occurs in approximately 0.5% of pregnant people, generally, and 8% in those with a previous history of miscarriage. Those with cervical weakness may require medication or a surgical procedure to keep the cervix closed until the pregnancy reaches term.
• Placenta previa: It is important in pregnancy to know if your placenta has implanted normally. About 4% of pregnant women receive the diagnosis of placenta previa at their 20-24 week ultrasound. A previa is when the placenta is low and covers all or part of the internal cervix. Most placenta previas resolve on their own and move away from the cervix as the uterus grows. However, bleeding from a previa can be very dangerous for a pregnancy, and persistent previas always require cesarean section for delivery.
• Placental abruption: Most likely to occur in the third trimester, placental abruption is when the placenta partly or completely detaches from the uterus. It happens in about 1% of pregnancies. If it is a serious form of abruption, it can cause heavy bleeding, Lamppa says, and can disrupt the blood supply to the baby.
• Preterm labor: When contractions result in the opening of your cervix after week 20 and before week 37 of pregnancy it is referred to as preterm labor. This often causes mild spotting and can cause symptoms such as abdominal pain or pressure, feelings of tightening, and changes in vaginal discharge.
• Uterine rupture: Though very rare and generally associated with severe pain, uterine rupture can also cause bleeding. It is a separation or tear in the uterus due to injury, multiple pregnancies, large fetus, previous scarring, or obstruction.
• Miscarriage (before the 20th week): Second-trimester miscarriages occur in 2% to 3% of pregnancies. Aside from bleeding, they may be accompanied by loss of fetal movement and cramping.
• Intrauterine fetal death: Another term for stillbirth, this is fetal death in the third trimester. Losses that occur in the final term are often caused by problems with the placenta, birth defects, infections in the fetus or placenta, as well as umbilical cord complications.
• Normal signs of labor: Bleeding right before labor is often normal as the cervix is softening and getting ready, Lamppa says. This includes the loss of the mucus plug, which blocks the cervical opening until the baby is ready for delivery.

When to see a doctor about bleeding during pregnancy

Because each situation is different, any incidence of bleeding should be discussed with a healthcare provider to determine the seriousness of it, Lamppa says. From there, the doctor can use your history and current medical information to assess whether further evaluation is needed.

An ultrasound and an exam are often helpful in determining the cause of bleeding, but sometimes the cause remains unclear.

"Largely it is determined by whatever your provider tells you based on your personal clinical situation," Lamppa says. "Generally speaking, if in the first trimester you know you have a viable intrauterine pregnancy with cardiac activity, that's a good sign."

Insider's takeaway

While bleeding during pregnancy can be scary, it does not always mean there is something urgently wrong. Although it can indicate conditions like miscarriage and ectopic pregnancy, it can also be a normal part of the pregnancy.

However, heavy bleeding may be a sign of danger for the mother or fetus, particularly in the second and third trimesters. Conditions like placental abruption can lead to heavy bleeding and, in severe cases, fetal death.

If you are experiencing vaginal bleeding while pregnant, it is important to tell your doctor, who will determine how best to proceed.

"Always check with your provider," Lamppa says. "Everyone's experience can be different, so report any changes, even if they seem mild."

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