The Timing of Implantation in Pregnancy

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Generally, implantation—when a fertilized egg, which has divided, multiplied, and turned into a cluster of cells called a blastocyst, attaches to the uterine wall—happens approximately between six to 10 days after ovulation.

This may seem like a detail that only concerns an OB/GYN, but knowing when implantation occurs is important to anyone trying to conceive. Implantation timing influences both how to time sex for pregnancy and when to take a pregnancy test (and ensure the most accurate results).

Ovulation and Implantation Timing

Implantation happens when a fertilized egg burrows into the uterine lining and begins to grow. When this can occur is dependent on overall cycle length, which is not necessarily the same for all women.

Ovulation typically happens 14 days prior to the beginning of menstruation. An egg is released from either the left or right ovary, after which it will live for about 24 hours unless it is fertilized. If it is not, the uterine lining is sloughed off.

This doesn't mean that you have to have sex at the exact moment of ovulation—just close to it.

That's because sperm can live for four to seven days inside the female body and meet up with an egg making its way through the Fallopian tube to the uterus. Sperm then breaks through the barriers surrounding the egg to fertilize it.

The fertilized egg then travels the remaining way to the uterus, a journey that takes several days. Implantation itself usually occurs between six to 10 days after the egg is fertilized.

Cycle Length Ovulation and Fertilization Implantation
28 days Day 14 Day 20 to 24
30 days Day 16 Day 22 to 26
32 days Day 18 Day 24 to 28

Implantation and Pregnancy Tests

Pregnancy tests are very specific about their timing because they test for the presence of a hormone called human chorionic gonadotropin (hCG).

Because hCG is produced by a developing placenta, the body cannot produce it until after implantation happens. This is why the levels of hCG in the body will vary depending on how long after implantation you take a pregnancy test.

In the very early stages of pregnancy, there is likely very little hCG in the urine because there hasn't been enough time between implantation and testing for it to build up in the body.

A pregnancy that has implanted four days prior to the expected start of your period is just beginning to send signals to the body. Testing this early is usually something that is not recommended unless there is a very specific reason, as false-negatives can occur.

Signs and Symptoms of Implantation

Most women do not have any specific signs or symptoms to indicate that implantation has occurred, but a small number of women experience a phenomenon called implantation bleeding around this time.

Implantation bleeding usually involves only very light spotting but occasionally can be confused for a menstrual period because of the timing, or even a first-trimester miscarriage.

For women tracking their basal body temperature (BBT) on a fertility calendar, a brief, one-day drop in BBT can occur during implantation. This is commonly referred to as an implantation dip and can indicate pregnancy in those who chart their BBT.

Typically, signs or symptoms of pregnancy do not occur immediately following implantation. Although not always the case, most women start to experience early pregnancy symptoms like nausea, fatigue, and breast tenderness around the time of their missed period.

Problems With Implantation

Most often implantation of an embryo happens without a hitch, but occasionally a problem may occur.

Ectopic Pregnancy

Occasionally, implantation occurs outside of the uterus. This is considered an ectopic pregnancy.

An ectopic pregnancy is often called tubal pregnancy because many of these pregnancies occur in the Fallopian tube. That said, some of these pregnancies also occur in places like the ovary, abdomen, or cervix.

Sadly, when the egg is not within the confines of the uterus, the pregnancy is not viable. Ectopic pregnancies are also dangerous for the pregnant woman, as they can cause severe hemorrhaging.

Treatment can include medication and/or surgery, which may involve removal of the Fallopian tube. Ectopic pregnancies can occasionally have ramifications in future pregnancies, including recurrence of ectopic pregnancy. However, most women go on to have subsequent successful pregnancies.

Late Implantation

When an embryo implants at the latter end of the six to 10-day implantation window, it is called late implantation. More specifically, late implantation is typically defined as that which occurs between the 8th and 10th day.

Implantation can occur successfully during this period and it is usually not a cause for concern.

However, some studies indicate an incremental increase in the likelihood of miscarriage the later the implantation happens, although the strength of this association is not yet fully understood.

While you can't control when or where an embryo implants, maternal smoking and older maternal age may make later implantation more likely.

Failure to Implant

Another issue that can occur is the failure of the embryo to implant. If this happens during a typical cycle of trying to get pregnant, you will likely have no way of knowing.

However, when using fertility treatments, you may know when an embryo does not successfully implant. When this happens three or more times in failed in vitro fertilization (IVF) attempts it is called recurrent implantation failure (RIF).

The causes of failure to implant are not always known but are thought to be a combination of uterine abnormalities (such as endometriosis, polyps, or infection) and/or embryonic abnormalities (often chromosomal).

Additional risk factors related to the parents may include smoking, age, body mass index, and stress.

A Word From Verywell

Implantation is a key milestone of the pregnancy journey, and understanding how and when it occurs can help you conceive and test.

The process of conception can seem daunting (and exciting), but know that as long as you regularly have sex, your chances of getting pregnant within a year are generally very high. In fact, 85% or more of couples conceive within one year of trying, with rates even higher for those younger than 30.

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Article Sources
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Additional Reading
  • Obstetrics: Normal and Problem Pregnancies. Gabbe, S, Niebyl, J, Simpson, JL. Fifth Edition.