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:
