What Is Implantation Bleeding?

Implantation bleeding is spotting or slight bleeding that occurs in early pregnancy, right around or just after you would normally expect your monthly period. Occurring in nearly 25% of pregnancies, implantation bleeding signals that a fertilized egg has implanted, or attached to the wall of a woman's uterus.

Implantation bleeding is not a sign that something is wrong; it does not affect the viability of a pregnancy. It does, however, indicate that you might be pregnant, so it's important to contact your gynecologist and discontinue activities that may affect your developing baby, such as drinking alcohol, smoking, or taking certain medications.

Why It Happens

Implantation bleeding is thought to be caused when a fertilized egg, or blastocyst, attaches to the lining of the uterine wall. The uterine lining is rich with blood vessels. At implantation, the fertilized egg pushes into the lining, breaking some blood vessels and causing a small amount of bleeding. That blood then leaves your body through your cervix.

Types of Spotting

Some women will mistake this blood as the beginning of their menstrual cycle or period. This is one of the reasons that your practitioner will ask you if your last period was normal.

If you have seen spotting or some bleeding and assumed it was your period, you may have miscalculated your due date, meaning you are further along than you originally thought. This can be a fairly common occurrence and one that doctors and midwives will screen for during your early prenatal visits.

Implantation bleeding can also be confused with other types of spotting, including bleeding near ovulation and an early miscarriage or chemical pregnancy (a nonviable pregnancy).

• Ovulation bleeding: Spotting that lasts one or two days and occurs about 14 days after the start of your period, when you ovulate and release an egg from the ovary
• Early miscarriage: Heavier flow with visible clots and a dark red color, as well as cramping and passing tissue through the vagina, that can occur five weeks after ovulation

Other reasons for spotting besides implantation bleeding include:

• Ectopic pregnancy
• Endometriosis
• Fibroids or polyps
• Infection
• IUI or IVF procedures
• Starting, stopping, or missing oral contraceptives
• Sexual intercourse
• Side effects of fertility drugs
• Thyroid disease
• Polycystic ovary syndrome (PCOS)

What to Look For

In general, implantation bleeding will be light and short (lasting no more than 48 hours) and occur between seven to 10 days after fertilization, or about a week after ovulation.

If you have a 28-day menstrual cycle and ovulate on day 14, for example, implantation would occur between day 20 and 24 of your cycle. If your cycle is longer, implantation would occur between four and eight days before your next expected period.

Depending on how long it takes for the blood to leave the body, it can be a range of colors, including:

• Light or dark red
• Pink or orange, if mixed with cervical mucus
• Brown

For some women, implantation bleeding is accompanied by mild cramps. In addition, you may experience early signs of pregnancy including:

• Fatigue
• Heartburn
• Insomnia
• Morning sickness
• Sore breasts

The only way to distinguish implantation bleeding from inter-menstrual bleeding or early miscarriage is by visiting your gynecologist, who will likely give you a physical exam along with an hCG blood test, which measures levels of the pregnancy hormone human chorionic gonadotrophin (hCG). At around week 6 to 8 of pregnancy, they may also perform an early pregnancy ultrasound to look for signs of pregnancy, including a yolk sac, fetal pole, and fetal heartbeat.

Next Steps After Implantation Bleeding

If you have unusually light bleeding around the time of your menstrual period and the bleeding does not turn into a heavier, normal flow, it's a good idea to take a pregnancy test and make an appointment with your gynecologist to confirm the pregnancy and begin your prenatal care. They may have you repeat the test to diagnose your pregnancy for their medical records.

Since implantation bleeding is a normal sign of early pregnancy, it does not require treatment. Your healthcare provider, however, will likely recommend avoiding the use of tampons during this time.

If the bleeding persists, becomes heavy or contains clots, you’ll need to contact your doctor right away, as this may indicate an early miscarriage.