All you need to know about embryo implantation

A major milestone in pregnancy, implantation remains, even today, quite unknown to the general public. What is it, what’s its purpose…?

We explain it all!

What is embryo implantation?

Once upon a time in the fascinating story of pregnancy: embryo implantation. When the sperm meets the egg, a small bundle of cells forms and travels along the fallopian tubes to implant in the uterus and settle into the endometrium. This is called implantation.

The endometrium is the highly vascularized layer of mucous membrane that forms and thickens each month in your uterus to welcome a potential embryo.

This implantation often causes slight bleeding at the beginning of pregnancy, known as “implantation bleeding”: the future placenta attaches to the endometrial vessels thanks to small projections that nibble into the endometrium, somewhat like Velcro.

When does implantation occur?

As we’ve seen, fertilization happens when the sperm, having successfully traveled up the tubes, meets the egg. The fertilized egg then becomes a “blastocyst” and migrates for about a week until it reaches the endometrium where it will implant. During this time, the little bundle of cells continues to divide.

The implantation process thus occurs about a week after ovulation, around 3 weeks of amenorrhea. The egg then divides into two distinct parts: one that will become the embryo and one that will become the placenta.

During an ultrasound, there’s not much to see yet, except for a small bubble: this is the gestational sac that will soon contain the embryo.

What are the symptoms of embryo implantation?

It’s not uncommon for implantation to cause slight vaginal bleeding at the time of implantation. This implantation bleeding can be more or less regular, making it difficult to distinguish from menstruation (especially true for women with irregular cycles or those who have just stopped taking the pill).

While missed periods are a good indicator of pregnancy, bleeding doesn’t necessarily mean you’re not pregnant. To be sure, it’s better to take a test 15 days after ovulation.

In general, other symptoms may indicate the start of pregnancy and therefore implantation, usually felt towards the end of the first month of pregnancy (or right after conception—these symptoms and how they are felt vary from woman to woman):

• a missed period (often the “little” detail that raises suspicion),
• an increase in vaginal discharge: under the effect of hCG hormones (which develop during pregnancy), the vaginal mucosa renews faster, increasing discharge,
• frequent urges to urinate,
• a feeling of breast tenderness (swelling and/or pain),
• digestive problems (diarrhea, constipation, heartburn, bloating),
• acne (caused by high estrogen and progesterone production),
• extreme fatigue, even drowsiness (especially after meals),
• nausea and vomiting (especially in the morning),
• a strong aversion to certain smells or foods,
• cravings or loss of appetite,
• noticeable weight gain or loss…

❗Most of these symptoms can also be associated with the menstrual cycle; only reliable tests and/or a blood test can precisely determine if a pregnancy has started.

Want to learn more? Feel free to download the May app, where you’ll find plenty of resources to support and guide you throughout your pregnancy.

What are the implantation success rates after IVF?

In the case of IVF, sperm are directly brought into contact with the eggs in a lab, and then the embryo is placed into the uterine cavity. Unfortunately, this technique doesn’t guarantee implantation.

In its latest national report, the Biomedicine Agency published the 2017/2018 evaluation results of medically assisted reproduction centers performing IVF in France. The national average live birth rate after a fresh or frozen embryo transfer is 28.4%.

How to confirm the start of pregnancy?

While the symptoms mentioned earlier are good indicators, they cannot confirm pregnancy on their own. Confirmation requires medical tests (which also help ensure that everything is progressing well for you and your potential future baby).

If you notice a missed period, you can first take a urine pregnancy test, available over the counter in pharmacies, grocery stores, supermarkets…

This test should preferably be done with the first urine of the morning, after the expected date of your period.

It detects the presence of beta-hCG, a hormone that appears about ten days after fertilization (the quintessential pregnancy hormone that ensures the secretion of estrogen and progesterone for the first 3 months). A test done too early may not be reliable.

If the test is positive, consult your doctor. A blood test can confirm or refute the urine test result. Your doctor may also prescribe a dating ultrasound.

This ultrasound is not necessary for all women. It’s mainly for women:

• with irregular cycles (who therefore do not fit the assumption that pregnancy starts 14 days after the first day of the last period), which creates a discrepancy in the estimated start date of pregnancy.
• with a history of ectopic pregnancy to check that the embryo has implanted in the right place.
• with a history of miscarriage.

It allows visualization of the gestational sac (or sacs) and potentially the presence of a hematoma or detachment. A hematoma or detachment does not necessarily endanger the pregnancy, but it’s important to be monitored by a healthcare professional.

What complications can occur during implantation?

Sometimes implantation does not happen or happens poorly, leading to a spontaneous pregnancy loss, commonly called a “miscarriage” (though this term is not very appropriate!).

Another implantation complication is an ectopic pregnancy (EP). There are about 16,000 cases per year, or 2% of pregnancies. In an EP, the egg implants outside the uterine cavity, most often in one of the fallopian tubes.

An ectopic pregnancy cannot result in a viable child. It must be stopped, whether spontaneously, medically, or surgically.

An ectopic pregnancy can be hard to identify early on: a woman with an EP may be asymptomatic, or her symptoms may resemble those of a “normal” pregnancy.

However, some women with an EP may experience abdominal pain (diffuse in the lower abdomen or localized to the lower right/left side) and brown or even blackish bleeding.

An EP can lead to tubal rupture if not identified quickly. This is internal bleeding, a medical emergency, requiring urgent care at gynecological emergency services.

Associated symptoms can include fainting (with or without loss of consciousness), severe abdominal pain, vomiting, shoulder pain radiating from the abdomen…

However, external bleeding is not necessarily a sign of tubal rupture or internal bleeding.

It is therefore important to consult a healthcare professional as soon as you suspect a possible pregnancy, to eliminate any risks.

Implantation is one of the very first stages of pregnancy. And what a stage! The uterus becomes the nest necessary for the development of a future baby! And it’s just the beginning of all that your body will accomplish over these 9 months.

Written by Sonia Monot with May’s expert team.

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Photo: ©Lazaro Rodriguez Jr, Pexels

This text was translated from French by an artificial intelligence. The information, advice, and sources it contains comply with French standards and may therefore not apply to your situation. Make sure to complement this reading by visiting the May ES/UK app and consulting the healthcare professionals who are supporting you.