What is implantation bleeding, and when does it occur?

Implantation bleeding 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. Implantation bleeding typically takes place between 7 and 14 days after conception.

Here is a closer look at a general timeline of ovulation, fertilization, and implantation:

  • Day 1. First day of menstrual period.
  • Days 14 to 16. Ovulation occurs (this can vary).
  • Days 18 to 20. Fertilization occurs.
  • Days 24 to 26. Implantation happens (about 6-10 days after ovulation), and implantation bleeding may occur for a few days.

How can you tell if what you’re experiencing is implantation bleeding? And when is vaginal bleeding something to be concerned about?

Implantation bleeding is fairly common and occurs in up to 25 percent of pregnancies. In many cases, it’s the first sign of pregnancy.

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 some major differences.

Regular period

  • Normal menstruation typically lasts less than 8 days and varies by age.
  • Bleeding often starts out heavy and lightens up toward the end.
  • Your period may be accompanied by severe uterine cramping, which can happen before bleeding and may continue for several days.

Implantation bleeding

  • does not usually last for more than 24 to 48 hours
  • bleeding is usually very light
  • much milder (or nonexistent) uterine cramping

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

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

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

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 patients who are Rh-negative and have vaginal bleeding during pregnancy, including in the first trimester. If you are unsure, you should 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.

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

  • bright red vaginal bleeding
  • heavy bleeding with clotting
  • significant pain or cramps.

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.

However, you should seek care immediately if you’re experiencing vaginal bleeding or pain.

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

  • dizziness
  • weakness
  • inability to keep down liquids

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

Unlike a normal period, implantation bleeding usually only lasts around 1 to 2 days.

Implantation bleeding occurs when a fertilized egg (blastocyst) 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 your 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.