At what week of gestation does implantation bleeding typically occur?

From the Guidelines

Implantation bleeding typically occurs around 10 to 14 days after conception, which is usually during weeks 3-4 of pregnancy. To clarify the timing:

• Week 1-2: Ovulation and fertilization occur
• Week 3-4: Implantation takes place Implantation bleeding is usually light spotting that lasts only a day or two. It's often mistaken for a light period, but it's generally lighter in flow and color (pink or brown rather than red). Not all women experience implantation bleeding. Although the provided studies 1 discuss first-trimester vaginal bleeding, they do not specifically address implantation bleeding. However, based on general medical knowledge, implantation bleeding is a common phenomenon that occurs when the fertilized egg attaches to the uterine lining. If you suspect you're pregnant and notice light spotting during this timeframe, it could be implantation bleeding. However, take a home pregnancy test or consult your healthcare provider for confirmation. Remember that any heavy bleeding or severe pain during early pregnancy should be reported to a doctor immediately. The bleeding occurs as the fertilized egg attaches to the lining of the uterus, causing minor disruption to blood vessels in the area. This process is crucial for establishing the pregnancy, as it allows the developing embryo to begin receiving nutrients from the mother's body.

From the Research

Implantation Bleeding

• Implantation bleeding typically occurs around 6-12 days after ovulation, which is approximately 1-2 weeks after fertilization 2.
• A study found that among pregnancies that lasted six weeks or more, the first appearance of chorionic gonadotropin (indicating implantation) occurred 6-12 days after ovulation, with 84% of women having implantation on day 8,9, or 10 2.
• Another study found that the median ovulation and implantation days were 16 and 27, respectively, with an ovulation to implantation interval of 11 days 3.
• In terms of gestational age, implantation typically occurs around 1-2 weeks after fertilization, which corresponds to around 3-4 weeks of gestation 4.

Gestational Age and Implantation

• A study found that early implantation leads to a larger crown-rump length (CRL) and late implantation to a smaller CRL at 10-14 weeks, independent of CRL growth rate 3.
• The same study found that gestational age estimated from CRL at 10-14 weeks was on average 1.3 days greater than that derived from ovulation timing 3.
• Another study found that the risk of early pregnancy loss increases with later implantation, with implantation on day 11 or later being associated with a higher risk of loss 2.

Vaginal Bleeding and Implantation

• A study found that vaginal bleeding during early pregnancy is generally light and not likely to be mistaken for a menstrual period 5.
• The same study found that bleeding tended to occur around the time when women would expect their periods, although rarely on the day of implantation 5.
• Another study found that early pregnancy bleeding is a common symptom, with 20-40% of pregnant women experiencing bleeding during the first trimester 6.