Implantation Bleeding

Reviewed by Dr. Temeka Zore OB/GYN, REICheckmark
Published: October 15, 2016

What Does Implantation Bleeding Mean?

Implantation bleeding is a name often attributed to mild bleeding that occurs in very early pregnancy that is said to be caused by the burrowing of a fertilized egg into the blood-rich uterine lining. This theory hasn't been proven in scientific studies and isn't probable based on the microscopic size of an embryo.

It is important to note that there is not a lot of scientific data surrounding implantation or implantation bleeding as it is difficult to study in human pregnancies. A lot of times implantation bleeding is a “diagnosis of exclusion” meaning a woman with bleeding in early pregnancy may get a work-up to determine the cause of bleeding and if no specific reason is discovered then it may be referred to as implantation bleeding.

Implantation bleeding may be referred to as early pregnancy bleeding.

FertilitySmarts Explains Implantation Bleeding

During the luteal phase of the menstrual cycle, the lining of the uterus typically increases in thickness and blood supply, in preparation for an embryo if fertilization of an egg occurs.

If an embryo is formed, it burrows into this blood-rich lining around day 5 when a blastocyst makes contact with the endometrium to 12 days after ovulation when it is fully implanted.

It is this burrowing of the embryo that is thought to cause a break in the maternal blood vessels and some blood may escape into the uterine cavity and out through the cervix, ultimately appearing as vaginal spotting.

What do we know about bleeding in very early pregnancy?

  • Bleeding that stops and then resumes is more likely to be detrimental to an ongoing pregnancy.
  • Studies on bleeding in very early pregnancy have not been able to confirm that bleeding in early pregnancy is a sign of implantation.

When does implantation bleeding occur?

  • One small study indicates bleeding in very early pregnancy is most likely to occur five days after implantation. Implantation was recorded as occurring from 27-31 days from the last menstrual period (LMP).
  • Bleeding is more likely around the start of the next expected menstrual period.

Implantation bleeding or period?

Early bleeding can be distinguished from menstrual bleeding by:

  • Length of Time. Implantation bleeding typically does not last more than three days while a period can be up to 7 days long.
  • Volume of Blood. Early pregnancy bleeding is typically light bleeding (defined as requiring 1 or 2 pads or tampons) in the first 8 weeks of pregnancy.

How common is implantation bleeding?

  • One small study showed 9% of pregnancies reporting light bleeding in the first 8 weeks of pregnancy.
  • First trimester bleeding of any kind is thought to occur in around 15-25% of pregnancies.

Other Potential Causes of Early Pregnancy Bleeding

Other potential causes of bleeding in early pregnancy or the first trimester include:

  • Anembryonic pregnancy or blighted ovum. A miscarriage where the fertilized egg implants but does not continue to grow.
  • Threatened miscarriage. A fetus is still inside a uterus but bleeding has occurred and the outcome of the pregnancy is questionable.
  • Ectopic pregnancy. When the embryo implants outside of the uterus, pelvic pain, nausea, and dizziness. It is a medical emergency.
  • Molar pregnancy. Abnormal development of the placenta leading to a mass within the uterus instead of a normal pregnancy
  • Low progesterone. One study suggests that early bleeding can be the result of a drop in levels of progesterone that may occur during the time period when the hormone stops being produced by the corpus luteum and when the placenta takes overproduction of the hormone.

Experiencing more than mild symptoms could be an indication of a more serious condition that requires medical attention.


Implantation Spotting

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