Not every case of spotting shortly after ovulation means your period is on its way. It could be implantation bleeding.

Implantation bleeding is a harmless sign that one of your eggs was fertilized during your last ovulation and has attached itself to the lining of your uterus.

In this article, we take a look at when and why implantation bleeding occurs, symptoms, and how you can tell it apart from other common causes of vaginal bleeding.

Early pregnancy bleeding is fairly common and may occur in up to 25 percent of the population. In many cases, it’s the first sign of pregnancy.

Implantation bleeding typically occurs within days of conception, when the embryo (or blastocyst) attaches to the uterine lining.

Some people mistake it for their regular period because it can look similar and occur near the time you’d expect your normal cycle. However, it’s typically lighter than a period and often happens sooner than your regularly scheduled menstruation, taking place between 7 and 14 days after conception.

Here’s a closer look at a general timeline of ovulation, fertilization, and implantation based on a regular 28-day cycle:

  • Day 1. First day of menstrual period.
  • Days 14. Ovulation occurs 14 days before your next menstruation.
  • Days 14 to 15. Fertilization occurs 0 to 1 day after ovulation (typically within hours of ovulation).
  • Days 20 to 24. Implantation happens about 6 to 7 days after fertilization, and implantation bleeding may occur for a few days.

The most common symptom associated with implantation bleeding is light bleeding or spotting, which typically lasts a few days.

Other symptoms are similar to those you may experience during your period or in the first trimester of pregnancy. These may include:

It can be difficult for people to know the difference between implantation bleeding and a regular period because symptoms can be similar enough to be mistaken.

Here are the primary differences:

Regular periodImplantation bleeding
Normal menstruation typically lasts less than 8 days and varies by age.Bleeding doesn’t usually last longer than 24 to 48 hours.
Bleeding often starts out heavy and lightens up toward the end.Bleeding is usually very light.
Your period may be accompanied by severe uterine cramping, which can happen before bleeding and may continue for several days.Uterine cramping is much milder or nonexistent.

When an egg has been fertilized, it begins traveling down a fallopian tube toward your uterus. The fertilized egg, called a “zygote,” typically enters the uterine cavity 3 days after fertilization. The zygote implants itself into the uterine wall about 3 to 4 days after it has entered the uterine cavity.

Implantation bleeding, if it happens, usually only lasts around 1 to 2 days.

As the fertilized egg embeds itself into the uterine wall to grow, it can rupture a small amount of blood vessels in the lining. This is why you might experience some bleeding.

There are many possible causes for vaginal bleeding during pregnancy. Doctors take it seriously and encourage pregnant people to report it.

If you’re not pregnant but also not 100 percent confident that your bleeding can be easily explained (by, say, your period), then you should report that to your doctor, too!

Here’s some more info on making the decision.

What symptoms should you call about?

Any unexplained bleeding or abdominal cramping is worth a visit to your doctor. In other words, unless you’re expecting your period, vaginal bleeding and pain are typically warning signs that something could be up.

Other symptoms can indicate a more serious issue, too. You should also talk with your doctor if you have symptoms like:

  • dizziness
  • weakness
  • inability to keep down liquids
  • fever

What symptoms should you get immediate medical attention for?

Although first trimester spotting is common, it could be serious if you experience:

These could be signs of miscarriage or an ectopic pregnancy, both of which require immediate medical attention.

Ideally, a person should seek preconception care and pre-pregnancy counseling if possible. You should seek care immediately if you’re experiencing severe or unusual vaginal bleeding or pain.

A healthcare professional will ask questions about your symptoms and medical history to determine the best course of treatment for you.

Your doctor may recommend blood tests, such as your blood type and Rhesus (Rh) factor, to determine if you need Rho(D) immune globulin. This is an injection given to those who are Rh-negative routinely between 27 and 28 weeks, and usually again within 72 hours of delivery. It’s also given to those who experience bleeding during pregnancy. If you are unsure about your blood type, talk with your doctor.

Even though not all bleeding is an emergency or a sign of complications, your doctor will likely want to perform tests, such as a vaginal ultrasound, to confirm if you’re pregnant and to make sure the fertilized egg has implanted in the uterus and isn’t ectopic.

Implantation bleeding occurs when a fertilized egg (zygote) attaches to the lining of your uterus. It may be confused with a regular period because of the symptoms it causes and the time it typically occurs. However, implantation bleeding is often much shorter and lighter than a regular period.

Although implantation bleeding is not usually a cause for concern, you should talk with a doctor if you experience symptoms like:

  • persistent bleeding
  • vaginal blood clots or bleeding that saturates a pad every 30 minutes
  • tiredness
  • dizziness
  • pain

Your doctor can help determine the cause of your symptoms and evaluate whether treatment is necessary.