Can implantation bleeding happen the day your period is due

Implantation bleeding is light bleeding that may happen about six to 12 days after conception. It may be caused by a fertilized egg implanting in the blood-rich lining of your uterus. Implantation bleeding can be an early sign of pregnancy, but some women mistake it for menstrual blood because it may happen around the time they expect their period.

Implantation bleeding

Implantation bleeding is light bleeding that a small percentage of pregnant women have at about six to 12 days after fertilization. Here's the theory behind why it happens:

After the sperm fertilizes the egg, it starts the three- or four-day trip from the fallopian tube to your uterus. During this time, it divides into hundreds of identical cells. Meanwhile, your ovaries release estrogen that causes the lining of the uterus (the endometrium) to thicken and develop more blood vessels. The uterine lining is preparing to host the quickly growing egg that will soon become an embryo.

Once the egg enters the uterus, it's called a blastocyst, a tiny ball of several hundred cells. A day or two later, it begins burrowing into the blood-rich lining of your uterus, where it continues to grow and divide. As it burrows into the endometrium, the blastocyst may cause little blood vessels to burst, resulting in a small amount of vaginal bleeding.

Implantation bleeding symptoms

In addition to light bleeding, some women also have these other implantation symptoms:

• Light cramping (less than with a normal period)
• Nausea
• Breast tenderness
• Lower back pain
• Mood swings
• Headaches

Note that these symptoms are no guarantee that you're pregnant – they can also be signs of ovulation or PMS. Taking a home pregnancy test is the best way to find out if you're pregnant. (Though you may have to wait a few more days to get an accurate result.)

If you do get your period instead of a positive pregnancy test, and haven't yet scheduled a preconception visit with a midwife or doctor, now is a good time to do so.

When does implantation bleeding occur?

Implantation bleeding tends to occur during the week before you would expect your period, or about six to 12 days after conception. This is around the same time a fertilized egg would be attaching itself to the uterine lining.

How long does implantation bleeding last?

Unlike a regular menstrual period, implantation bleeding usually lasts no more than a day or two. This is the amount of time it takes for the fertilized egg to become implanted into the lining of the uterus.

How common is implantation bleeding?

By some estimates, about 15 to 25 percent of women experience implantation bleeding. Some women may think they’re having a light period when they see the spotting. They may not realize they're pregnant.

How can I tell if it's implantation bleeding or my period?

Here's how to tell whether your bleeding is more likely to be implantation bleeding or your period:

• Amount of blood. Implantation bleeding is a lot lighter than a typical period. It's usually just a little spotting.
• Length of time. Most women bleed for three to seven days during their period. Implantation bleeding often lasts only one to three days.
• Color. Menstrual blood is usually bright red or dark red, but implantation bleeding tends to be a light pink, brown, or rust discharge.
• Clotting. Many women bleed enough during their period that some of the blood clots or becomes like a gel. Implantation bleeding is too light to clot.

When to see a doctor for bleeding in early pregnancy

If you continue spotting even after a positive pregnancy test, or if you develop other symptoms (such as pelvic or abdominal pain, dizziness, or lightheadedness), call your provider immediately.

You may need an exam to make sure you don't have an ectopic pregnancy. This happens when the fertilized egg grows outside the uterus, usually in a fallopian tube. (It's possible to have an ectopic pregnancy even if you don't get a positive result on a pregnancy test.)

Bleeding or cramping in early pregnancy may also be a sign of an impending miscarriage. But many women spot in the first trimester for no apparent reason and go on to have a completely normal pregnancy.

Learn more:

Quiz: Am I pregnant?

Video: What is implantation bleeding?

During pregnancy, your body goes through all kinds of changes. Some are obvious and expected, like a growing belly or the stoppage of your menstrual cycle. But did you know that very early on, you may experience some bleeding that could be mistaken for your period? This is called implantation bleeding, and we sat down with Heather Reed, MD, an obstetrics and gynecology physician and medical director of labor and delivery at Banner – University Medical Center Tucson, to learn what it is and when you should be concerned.

Q: What is implantation bleeding? Is it normal?

A: Pregnancy starts when an egg is fertilized in the fallopian tube and then makes its way to the uterus. When the fertilized egg reaches the uterus, it attaches to the uterine wall. When this attachment happens, you may experience a small amount of bleeding. This is called implantation bleeding and it is completely normal.

Q: How much bleeding is normal?

A: The amount of bleeding at implantation can vary between women. Some women may not experience any bleeding with implantation, while other women may have bleeding that compares to a light period and lasts two or three days. Anything on that continuum – from no bleeding to bleeding resembling a light period – can be considered normal.

Q: I’m experiencing bleeding that is heavier than a light period. Should I be worried?

A: Because implantation can be the same time as you might be expecting your period, it can be hard to tell the difference between implantation bleeding and your regular menstrual bleeding. It’s tough to know when you should be worried because every woman’s circumstance is different. However, any time bleeding saturates a pad in less than two hours it should be considered too much vaginal bleeding, and you should consult a physician.

Q: Are there other symptoms associated with implantation bleeding?

A: Some women experience slight cramping or nausea during implantation, in addition to light bleeding. Because implantation occurs so early in pregnancy it can be difficult to tell if the symptoms are from implantation or your regular monthly menstrual cycle.

Q: How do I know the difference between implantation bleeding, my menstrual period, and a miscarriage?

A: Unfortunately, there’s no way to tell the difference between implantation bleeding and menstrual bleeding. Implantation occurs 6-12 days after conception, which is around the same time you may be expecting your monthly period, and both can produce the same amount of bleeding.

If you think you may be pregnant, your best bet is to take a home pregnancy test. The level of human chorionic gonadotropin (hCG), a pregnancy hormone, can vary between women but most home pregnancy tests can detect pregnancy. However, it’s important to know that a home pregnancy test can produce a false negative because everyone’s hormone level is slightly different. While it’s possible to become pregnant and lose the pregnancy this early on – resulting in light bleeding that could be confused with implantation bleeding – a pregnancy loss this early isn’t considered a miscarriage.

If you think you’re pregnant, it’s best to make an appointment with an OBGYN. An OBGYN can provide a pregnancy blood test and if you are pregnant, start important prenatal care right away.

For additional information, check out these related articles: Is My Period Normal? — 7 Signs You Might Be Pregnant — Things You Should Know About Well-Women Visits. And for other helpful advice regarding pregnancy, visit the Banner Health blog. 

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