Implantation Bleeding: Everything You Need to Know

Implantation bleeding is a normal physiological event, which occurs 10 days after fertilization. It doesn't indicate a pregnancy problem.

Written and verified by el biólogo Samuel Antonio Sánchez Amador.

Last update: 30 May, 2021

Implantation bleeding (commonly known as a false period) is a type of vaginal bleeding that can occur in pregnant women during the early stages of pregnancy. This bleeding is very scarce, it is considered a normal physiological event, and isn’t associated with risks in fetal evolution and development.

Normally, it occurs 10 to 14 days after fertilization of the ovum, but implantation bleeding has been recorded up to 8 weeks from gestation. If you want to know everything about this common (but innocuous) event, we encourage you to continue reading!

Implantation and the miracle of life

As indicated by the ORG Assisted Reproduction portal, embryo implantation is the process by which the embryo, which is approximately one week old, adheres to the maternal endometrium and enters the gestation period. The endometrium is the inner part of the uterus, which allows the formation and development of the placenta in pregnancy.

The steps from the fertilization of the ovum to the definitive implantation can be described as follows:

1. Day 1: Fertilization occurs (union of the egg and sperm, haploid gametes) and the zygote is formed. The zygote is a cell resulting from fertilization, but, unlike gametes, it has 2 complete sets of chromosomes (one from the father and one from the mother).
2. Days 2 and 3: Segmentation of the zygote into several cells, from 2 to 32 units, occurs through mechanisms of mitosis. The structure derived from this process is known as a morula.
3. Days 4 and 5: When the morula reaches a content of 32 cells, on day 4 the formation begins to differentiate. The morula is considered to transform into a blastula when it reaches a content of 64 cells. In the blastocyst, there is a liquid internal cavity (blastocele) surrounded by 2 cell layers.
4. Days 5 and 6: The blastocyst attaches to the posterior wall of the uterus.
5. Days 7 and 8: The blastocyst is superficially implanted in the endometrium, a tissue that lines the inner wall of the uterus, highly vascularized and thickened. When it isn’t implanted (when there’s no fertilization), the walls of the endometrium shed, leading to menstrual bleeding.
6. From 9 to 13 days: The blastocyst undergoes multiple morphological changes and adhesion occurs. We aren’t going to focus on the specifics of the process today.
7. Day 14: Implantation is fully completed. The blastocyst has completely entered the endometrium.

Although it’s a very interesting process, we haven’t told you all this information for pleasure. According to the Mayo Clinic, it appears that implantation bleeding takes place, as the name suggests, when the blastocyst implants in the endometrium. This event is conceived between 10 and 14 days after fertilization, and it’s totally normal.

What is implantation bleeding?

As the American College of Obstetricians and Gynecologists (ACOG) indicates, vaginal bleeding during pregnancy has many possible causes. In general, if this is mild and occurs during the first few weeks, the patient shouldn’t worry. On the other hand, false periods during late pregnancy have a worse prognosis.

As we have said, implantation bleeding is suspected to occur when the blastula implants into the endometrium, a normal event necessary for the pregnancy to run its course. It’s estimated that it occurs in 25% of pregnant women and, on some occasions, it’s the first sign that the female is pregnant.

Before continuing, we must clarify what we can class as mild bleeding, and what is severe. In the following list, we will clarify both terms and more:

1. Spotting or spots: as the name suggests, spotting manifests itself in the form of spots or spots on underwear. It is brownish in color and appears outside the menstrual phase. For many women, it’s quite a normal occurrence.
2. Light bleeding: Bleeding outside the menstruation period is considered light when it involves a blood loss of less than 50 milliliters.
3. Heavy bleeding: 50 to 1,000 milliliters of blood lost, but no signs of circulatory shock.
4. Massive blood loss: When the pregnant woman loses more than 1,000 milliliters of blood, with or without signs of circulatory shock. Typical symptoms of circulatory shock are hypotension, tachycardia, and signs of poor peripheral perfusion. This is a medical emergency.

Implantation bleeding usually occurs in the form of spotting, although it can also be a minor bleeding that requires the use of a tampon. Be that as it may, it should never manifest as heavy bleeding.

Symptoms of an implantation bleeding

The most common symptoms of implantation bleeding are mild spotting episodes. Many women say that this blood is different from the normal period, because it has a darker tone. Additionally, some patients may experience mild cramps, mild dizziness, slightly swollen breasts, and a headache.

On the other hand, it’s also common for women to confuse implantation bleeding with the start of a normal period, when they don’t know they’re pregnant. Unfortunately, there’s no way to reliably differentiate between the two events with the naked eye, so the only thing that clears this up is a normal pregnancy test.

The difference between light and heavy bleeding

When there’s noticeable bleeding beyond 20 days of gestation, it’s time to get a little more pessimistic. According to the MSD Manuals portal, in almost all cases this is an indication that a preventable miscarriage is going to occur (threatened abortion) or that, failing that, the death of the fetus is completely certain (inevitable abortion).

A miscarriage is considered as such when the fetus dies before the 20th week of pregnancy. Many people suffer this type of loss because, without going any further, 10 to 20% of pregnancies end in this way. It’s normal to have feelings of grief and loss at this stage, but it’s necessary to understand that it’s quite normal.

When the fetus has cells with an abnormal number of chromosomes, and the mother has serious diseases (such as diabetes or aggressive infections) or uterine abnormalities, then miscarriage is common. As indicated by the Las Condes Clinic, 70% of spontaneous abortions find their cause in embryonic genetic alterations.

In any case, implantation bleeding doesn’t usually last more than 48 hours, while the normal period is conceived in an interval of 3 to 7 days in duration. Also, uterine cramps are always less severe (or not even experienced).

Danger signs

However, miscarriage doesn’t have to pose a danger to the mother if it’s managed correctly in the medical setting.

If you think you are experiencing copious episodes of implantation bleeding, look out for the following symptoms, as it may be a miscarriage that requires immediate medical attention:

• Fainting, dizziness, and palpitations – These are indicative of hypotension, one of the most typical signs of circulatory shock. In general, fainting is caused by too low blood pressure.
• Very high blood loss or blood ejection with large tissues and/or thrombi… these aren’t signs of implantation bleeding, but worse. They can indicate an ectopic pregnancy, that is, an implantation of the fetus outside the main cavity of the uterus.
• Very current abdominal pain, which worsens when changing position or making minimal effort.
• Fever, chills, and vaginal discharge containing blood mixed with pus. The presence of pus is often indicative of a bacterial infection, which in this case has become severe.

In all these scenarios, we can assure you that the patient isn’t facing normal implantation bleeding. The most probable case is that something has gone wrong during the pregnancy and, therefore, it’s essential to go quickly to the emergency center.

The threat of ectopic pregnancy

According to the Elsevier medical portal, 1 to 2% of all pregnancies are ectopic, despite the figures having stabilized in recent years. As the incidence increases, mortality increases, but this serious event continues to be the cause of the death of 15% of pregnant mothers.

The most common implantation site of the fetus (98% of cases) is the fallopian tubes. These are the places where the eggs travel from the ovaries to the uterus. If the fertilized egg grows inside one of these ducts, it can break it and cause very profuse internal abdominal bleeding in the mother. If left untreated, this is deadly.

With these data we do not want to scare anyone: implantation bleeding is never a symptom of ectopic pregnancy. However, it’s necessary to differentiate the milder stages of the last event with normal bleeding. When in doubt, it’s always best to see a medical professional.

A normal event

As we have said before, up to 25% of women suffer implantation bleeding during the first week or week and a half after fertilization of the ovum. It’s quite normal and doesn’t cause any harm to the mother, as it occurs in the form of a slight drip and doesn’t last more than 48 hours. Therefore, it isn’t a cause for concern.

On the other hand, if the bleeding becomes chronic or copious, it’s necessary to go quickly to a medical professional in all cases. Whether this is a sign of an ectopic pregnancy or a spontaneous miscarriage, it should always be dealt with in the emergency room.