fertilization and implantation timeline?

Implantation symptoms: Signs, timeline, and testing

How implantation works
Symptoms
Other early symptoms
Timeline
Other causes
Taking a test
Summary

Implantation is a critical early stage in every pregnancy.

This article explores the signs that implantation has happened. It also reviews a few false signs of early pregnancy and suggests when to take a pregnancy test.
Some signs of implantation include cramping and spotting.
How implantation works

An egg is fertilized by a sperm in one of the two fallopian tubes. These connect the uterus with the ovaries, which sit to either side.

The fertilized egg is called a zygote, and it travels down the tube toward the uterus. As it moves, it divides and grows, becoming a multicellular structure called a blastocyst.

The first stage of implantation occurs when the blastocyst attaches to the lining of the uterus, a mucous membrane called the endometrium. The blastocyst then buries itself in the uterine wall.
Timing

Implantation is a complex process with a brief window — it happens about 6–10 daysTrusted Source after ovulation.

One factor influencing the timing is that the endometrium changes, thickening and shedding, throughout the menstrual cycle. It is only receptive to a blastocyst for a few days in each cycle.

Even if the timing is right, implantation may not happen. According to researchersTrusted Source, a lack of implantation is a common cause of early pregnancy loss.
Implantation symptoms

Indications that implantation has happened can include bleeding and cramping.

Implantation bleeding is spotting or light bleeding that takes place about 1–2 weeks after fertilization. It is usually short-lived and lighter than a normal period. The blood is often paler than menstrual blood or can be a rusty brown.

There has been little research about implantation cramping, but it may affect the lower abdomen or back and feel like:

light pulling
tingling
pricking

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Other early pregnancy symptoms

Early pregnancy can cause additional symptoms, which may start a short time after implantation and continue for the first trimester and sometimes beyond. They can include:

tiredness
feeling very emotional
nausea
vomiting, especially in the mornings, often from around 6–9 weeks
a headache
heartburn
having enlarged or tender breasts, sometimes with the nipples sticking out
needing to pee more frequently
constipation
a strange taste in the mouth
food cravings and aversions
changes in weight

Some pregnant people experience many of these symptoms, while others experience none.
Implantation timeline

A timeline of implantation and early pregnancy includes the following events, based on a 28-day menstrual cycle:

Day 1: the first day of a period
Day 14: ovulation
Day 15: fertilization — the egg can be fertilized for about 24 hours after ovulation
Day 20–24: implantationTrusted Source of the blastocyst in the uterus

Other causes of similar symptoms

The following symptoms can indicate implantation, but they can also have very different causes, including pregnancy loss.
Bleeding

Vaginal bleeding occurs during 15–25% of early pregnancies, according to The American College of Obstetricians and Gynecologists. It can be a sign of implantation, but it can instead point to:

a miscarriage
an ectopic pregnancy
bleeding from the cervix, due to increased blood flow to the area
an infection

Also, bleeding sometimes happens due to a pelvic examination, sex, or a Pap smear.
Cramping

Cramping or lower back pain can indicate implantation, but it can also occur with early pregnancy loss.

Because pregnancy tests are now so sensitive, some people know when they have experienced a very early pregnancy loss, known as a chemical pregnancy. The loss occurs at just around 5 weeks.

Also, a person might confuse implantation bleeding and cramping with a period, though any symptoms of implantation usually take place a week or so before a period is due.

Often, light bleeding, spotting, and cramping in early pregnancy resolve with no problems.

However, anyone experiencing bleeding or more serious pain should consult a doctor. These may be, for example, symptoms of an ectopic pregnancy, which is a medical emergency.

In addition, pregnant people with rhesus-negative blood may need an injection of rhesus immune globulin after any bleeding, to prevent the fetus from developing health issues such as hemolytic anemia, according to the National Heart, Lung, and Blood InstituteTrusted Source.
When to take a pregnancy test

Home pregnancy tests detect the hormone human chorionic gonadotropin (hCG) in urine.

The pregnant body starts producing this hormone before implantationTrusted Source. Levels in the blood and urine double about every 24 hours Trusted Sourcefor 8 weeks, peaking at about 10 weeks.

Home pregnancy tests can detect hCG in the urine about 12–15 daysTrusted Source after ovulation, in people with 28-day menstrual cycles.

A positive pregnancy test result may be possible on the day a missed period is due. However, the tests are not so reliable that a negative result at this stage definitely means that the person is not pregnant.

The American Association for Clinical Chemistry suggest that in this case, a person should test again about 10 days after the period was due.
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Summary

Implantation is a complex process essential to the establishment of a pregnancy.

It is sometimes accompanied by spotting or light bleeding, and the blood may be pale pink or rusty brown. Some people experience cramping.

However, bleeding and cramping can indicate a range of issues, including pregnancy loss, and are not a reliable indicator of implantation.

For greater certainty, use a home pregnancy test at least 10 days after a missed period, though some tests can detect pregnancy earlier, on the first day a period was due.