It can be disconcerting to find yourself bleeding when you're trying to get pregnant. Is what you're seeing your period? Or are you actually pregnant, and that blood is an indication of implantation bleeding — the light bleeding that can happen after fertilization?
In this piece, we'll supply you with all you need to know about implantation bleeding, including why it happens, for how long, and how to tell the difference between implantation bleeding and your period. But here are the biggest takeaways first:
- Implantation bleeding about 10-14 days after an egg is fertilized is normal, but not everyone experiences it.
- If implantation bleeding happens, it's likely around the same time you'd get your period — and about one day after your body starts producing the pregnancy hormone that tests pick up on.
- Doctors diagnose implantation bleeding by first ruling out pregnancy complications like ectopic pregnancy or miscarriage.
- The best way to know for sure that you're pregnant is to take a pregnancy test two weeks after ovulation — though you can start using early pregnancy tests, like ours, as early as six days before your missed period.
- If you find out you're pregnant, reach out to your healthcare provider within 24 hours if you have bleeding that lasts longer than a day — and immediately if you have moderate to heavy bleeding, if you pass tissue from your vagina, or if you have cramping, fever, chills, or abdominal pain along with any amount of vaginal bleeding.
Now that we've covered the TL;DR, let's dive deeper!
What is implantation bleeding?
Once an egg has been fertilized by sperm and becomes an embryo, it travels to the uterus and embeds itself into your endometrium (aka uterine lining) about 1-2 weeks after fertilization — this is what's known as implantation.
"Implantation bleeding is defined as a small amount of spotting that occurs 10-14 days after fertilization and just happens to correspond to the first day of the missed menstrual period," explains OB-GYN and Modern Fertility medical advisor Dr. Eva Luo, MD, MBA. Implantation bleeding may also occur about one day after your body starts producing human chorionic gonadotropin (hCG), the pregnancy hormone that home pregnancy tests look for.
How do you know if you're experiencing implantation bleeding?
You might see implantation bleeding when you wipe after going to the bathroom, or it might appear in your underwear. It's possible that this bleeding will be accompanied by mild cramping, as well as other early pregnancy symptoms, such as:
- Nausea (with or without vomiting)
- Tender breasts/chests
Because not everyone experiences implantation bleeding, has pregnancy symptoms (or has them to the degree that they recognize them as pregnancy symptoms), and because implantation bleeding generally occurs around the time of your period, the best way to assess whether or not you're pregnant is to take a test. hCG begins increasing around two weeks after ovulation if that released egg is fertilized, so that's the best time to start testing. (You can start using our Pregnancy Test as early as six days before your missed period!)
Why can implantation bleeding happen?
"We think implantation into the endometrial lining causes some bleeding," says Dr. Luo. The endometrium has thickened during the menstrual cycle in preparation for a potential pregnancy — and it's possible that the embryo (aka fertilized egg) implanting itself into that lining could trigger spotting. But as we'll explain in the next section, the importance of implantation bleeding is more about what it isn't than what it is.
All that said, it's worth noting that one 2003 study that looked at the bleeding patterns of 211 women who were trying to get pregnant found no connection between the act of implantation and bleeding. So think of implantation bleeding as more of a science-backed hypothesis than a hard-and-fast truth.
Do you need to have implantation bleeding for a healthy pregnancy?
No, you don't need to experience implantation bleeding for a healthy pregnancy — and not experiencing implantation bleeding doesn't mean your pregnancy isn't viable (i.e., whether or not the fetus will go to full term).
"Implantation bleeding is what we call a diagnosis of exclusion. Meaning, only when everything else has been ruled out do we consider implantation bleeding," explains Dr. Luo. "What I want to ensure is that this is a viable intrauterine pregnancy — and that means ruling out an ectopic pregnancy and miscarriage," which bleeding during a pregnancy may indicate in some cases (more on this in a bit).
The big question: Is it implantation bleeding or your period?
So how can you tell if what you're seeing in your underwear or on toilet paper is an early sign of pregnancy or your period? Let's break down the differences.
Everyone's period may look a little different, so keep in mind what "normal" means for you when considering whether or not you could be experiencing implantation bleeding.
What else could cause bleeding during pregnancy?
It's totally normal to be concerned if you're bleeding while pregnant, but it doesn't always mean anything is wrong. According to the American College of Obstetricians and Gynecologists (ACOG), 15%-25% of pregnant people experience bleeding during the first trimester.
"Depending on when the bleeding occurs, this can ultimately mean close monitoring with blood labs every 48 hours and ultrasounds," says Dr. Luo. However, "the vast majority of bleeding, if not miscarriage or ectopic, often goes unexplained and the pregnant person ends up with a lovely term delivery."
Let's take a look at some reasons for bleeding in the first 12 weeks of pregnancy:
- Spotting after penetrative sex when you're pregnant may happen. Your cervix is developing blood vessels during pregnancy, so it's extra sensitive.
- Subchorionic hematoma or hemorrhage is a common cause of bleeding in early pregnancy. It occurs when there's bleeding under one of the membranes that surrounds the embryo inside the uterus. Most of the time, this condition goes away on its own, but follow-up is important for a healthy pregnancy.
- Ectopic pregnancy is a rare (2 out every 100 pregnancies) but urgent condition that requires medical attention. It occurs when an embryo implants outside of the uterus, often in the fallopian tube. An ectopic pregnancy cannot be carried to term, and can cause internal bleeding (which could be life-threatening) if it's not treated. Vaginal bleeding is one indication of an ectopic pregnancy; others are cramps, dizziness, weakness, and pain in your lower back, abdomen, and pelvis.
- Chemical pregnancy, or very early pregnancy loss, often occurs before someone even knows they're pregnant. Chemical pregnancies make up 8%-33% of all pregnancies, and 18%-22% of in vitro fertilization (IVF) pregnancies. Bleeding and cramps may be signs of early pregnancy loss.
If you're in early pregnancy, the Mayo Clinic recommends contacting your healthcare provider within 24 hours if you have vaginal bleeding that lasts longer than a day, and contacting them immediately if you have moderate to heavy bleeding, if you pass tissue from your vagina, or if you have cramping, fever, chills, or abdominal pain along with any amount of vaginal bleeding.
Implantation bleeding is an early sign of pregnancy that, when identified, rules out complications like an ecoptic pregnancy or miscarriage. It's light, stops on its own, and usually goes away within a day or two — if it's as long as your period, it's not implantation bleeding. Not everyone experiences it, and if you don't, it doesn't mean anything about your pregnancy.
There are a lot of reasons you might be bleeding or spotting other than pregnancy, though, so when in doubt, take a pregnancy test and don't hesitate to contact your healthcare provider. It can be overwhelming not to know what's going on, but Modern Fertility and your healthcare provider are always here to help you get to the bottom of things.
This article was medically reviewed by Dr. Eva Marie Luo, MD, MBA, OB-GYN at Beth Israel Deaconess Medical Center and Clinical Lead for Value at the Center for Healthcare Delivery Science at Beth Israel Deaconess Medical Center.