• Blood may appear black after exposure to oxygen in your uterus — this is completely normal.
  • Implantation, an object left in your vagina, miscarriage, or an STI can also cause black blood. 
  • If you continue to experience dark bleeding with pain or other symptoms, call a doctor right away.

A small amount of black blood could happen for a number of reasons, including implantation or a missed miscarriage. But as long as the spotting remains minor, you usually don't need to be concerned.

Black blood is simply blood that has been inside your vagina or uterus long enough to oxidize after exposure to oxygen. This turns it darker, giving it the color you perceive as black, says Dr. Alan Lindemann, obstetrician and maternal mortality expert at PregnancyYourWay.com. 

But black blood doesn't always mean you're pregnant. Read on to learn why you might notice blood that appears black and what to do next. 

Causes of black blood during or after pregnancy

Black blood during or after pregnancy happens for four main reasons: 

1. Implantation bleeding

Implantation bleeding, which typically occurs within two weeks after conception, happens when a fertilized egg attaches to the inner lining of your uterus. This bleeding typically lasts less than three days, and you may mistake it for spotting.

This blood will usually range in color from dark brown to light pink, but very dark brown blood could appear black. 

With implantation bleeding, you might also experience some light cramping, swollen or tender breasts, fatigue, and nausea or vomiting. 

What to do next: If you think you could be pregnant, a good next step involves taking a home pregnancy test. A healthcare professional can confirm a positive test result. 

2. Miscarriage

Most miscarriages occur within the first 13 weeks of pregnancy, but many happen before you realize you're pregnant.  

In some cases, black blood can suggest miscarriage, though you'll likely also notice other symptoms, including: 

In some rare cases, black blood could suggest a septic miscarriage, which can be life threatening. 

What to do next: If you notice a large amount of black blood along with other signs of potential miscarriage, you should contact your doctor immediately, says Dr. Aaron Gelfand, Obstetrics & Gynecology Physician at ChoicePoint. 

3. Postpartum lochia

After giving birth, you'll bleed for about four to six weeks. This postpartum bleeding, called lochia, starts out heavy and dark with plenty of clots. It also contains mucus, excess white blood cells, and pieces of your uterine lining. 

The first stage of lochia, which lasts up to several days, may appear black at times. 

What to do next: Lochia is a natural part of giving birth, and it gradually resolves on its own after about six weeks. But if you experience an atypically large amount of bleeding, such as filling one or more pads an hour, make an appointment with your doctor as soon as possible to rule out a possible postpartum hemorrhage (PPH).

4. Placental abruption

Placental abruption, the premature detachment of the placenta, occurs in about one in every 120 pregnancies. If this happens, you'll experience bleeding, typically dark red or almost black in color, though the amount of blood will depend on the size of the area that detached. 

Other symptoms of a placental abruption may include: 

  • Extreme thirst
  • Nausea
  • Feeling dizzy or faint
  • Abdominal pain
  • Uterine contractions
  • Blood in the amniotic fluid

What to do next: Not all placental abruptions cause external bleeding, so it's important to contact your doctor immediately if you experience any of the above symptoms during the second trimester. 

Your doctor may perform a physical exam, ultrasound, and monitor the fetal heartbeat to determine if you have a placental abruption. 

Your specific treatment will depend upon how far along you are and how severe the abruption is. Depending on the circumstances, your care team may suggest close observation or recommend inducing labor immediately.

Other possible explanations for black blood or discharge

Black blood or discharge doesn't always relate to pregnancy. Other potential causes include:

1. The beginning or end of your period

It's pretty common to experience black spotting or discharge on either end of your period. 

Since blood oxidizes over time, and you often shed old blood at the beginning of your period, your initial discharge may appear black, dark brown, or similar in color and texture to coffee grounds, Gelfand says. 

Depending on how slow your flow is, the blood in your uterus may have enough time to oxidize before it leaves your body. But if you notice black blood once your period ends, you should reach out to your doctor as soon as possible — this could signal the presence of an infection or foreign object.

2. A foreign object in your vagina

Black discharge outside of your regular menstrual cycle could suggest a foreign object in your vagina, such as a forgotten tampon, sex toy, condom, or other contraceptive devices. 

Any of these can cause irritation and lead to an infection, which may include black discharge as one possible symptom. 

If you do have an infection, you might also notice: 

  • Discharge that smells foul, fishy, or rotten
  • Discomfort or itching
  • A rash or swelling in your genital area
  • Trouble urinating or pain when urinating
  • Fever
  • Abdominal pain

What to do next: If you've noticed any of the above symptoms, it never hurts to do a quick check and make sure nothing's stuck in your vagina.  

If you can't remove the object yourself, get medical attention right away. Without treatment, the infection could get worse or lead to toxic shock syndrome (TSS), which can be fatal.

3. Sexually transmitted infections (STIs)

Chlamydia and gonorrhea are two of the most common STIs associated with dark vaginal discharge, bleeding, or foul-smelling discharge.

Your symptoms can vary, depending on which STI you have, but common symptoms include:

  • Pain or burning when urinating
  • Vaginal itching
  • Spotting or bleeding between periods
  • Bleeding and pain during or after sex

What to do next: If left untreated, STIs can worsen and may lead to pelvic inflammatory disease (PID) or infertility. 

If you have any of the above symptoms, it's best to make an appointment for testing right away. A healthcare professional can make a diagnosis and prescribe the right treatment.

Treatment for STIs generally includes:

  • A round of antibiotics or antiviral medications
  • Abstaining from sex during the treatment period
  • Testing and preventative treatment, if needed, for your partner(s)

4. Cervical cancer

Black blood could be a possible sign of cervical cancer, although this type of cancer is less common in the United States. The blood can appear as spotting between periods, bleeding after menopause, and longer or heavier periods than usual. With cervical cancer, blood will often appear chunky and have a foul smell.

Cervical cancer often doesn't involve early symptoms, but you could notice:

  • Itching or burning during urination
  • Blood in your urine
  • Pain during sex

What to do next: These symptoms can have a number of causes, so it's always best to make an appointment with your doctor. They can do a pelvic exam and Pap smear and recommend next steps, depending on your results. 

Insider's takeaway

Black blood may suggest implantation bleeding, which can happen as a sign of conception. So, if you notice black spotting and haven't had a period, you may want to consider taking a pregnancy test.

You may also notice black blood during your regular menstrual cycle, usually at the beginning or end of your period. But there's no need for concern — this just means your blood has taken a little longer to leave your uterus. 

If you experience a consistent, heavy flow of dark red or almost-black blood, along with symptoms like pain, fever, nausea, or dizziness, you'll want to get medical attention right away.

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