What is embryo implantation?

Embryo implantation is a complex process whereby the embryo in the blastocyst stage (fifth day of development) attaches to the maternal endometrium, thereby initiating pregnancy and intrauterine development.

This process marks the beginning of clinical pregnancy and can only be successful if the endometrium is receptive, in what is known as the implantation window, which occurs between days 6 and 10 after ovulation.

Embryo implantation: stages and symptoms

After undergoing fertility treatment, many women want to know if they are pregnant and look for symptoms that may indicate whether they are. Is this your case? Keep reading! At Fertility Madrid, we will tell you what these symptoms are.

But to introduce the topic, let's take it step by step.

What are the stages of implantation?

Embryo implantation is a critical stage in the human reproduction process. After fertilisation, the fertilised egg, known as a zygote, begins to divide and form a more complex structure called a blastocyst. The blastocyst travels through the fallopian tubes to the uterus, where it looks for a suitable place to implant.

Implantation usually occurs around 6 to 10 days after fertilisation. During this process, the blastocyst attaches to the innermost layer of the uterus, called the endometrium. Once implantation is successful, the embryo begins to release hormones that are essential for maintaining pregnancy and stimulating the growth of placental tissue.

We can divide the embryo implantation process into four consecutive phases:

1. Apposition: The first phase of embryo implantation is called apposition or receptivity dialogue. In this phase, the blastocyst comes into contact with the endometrium and begins to release proteins that help it attach to the uterine wall. The endometrium also releases proteins that help the blastocyst implant.
2. Adhesion: In this phase, the blastocyst attaches firmly to the uterine wall. This is because the blastocyst releases proteins that bind to receptors in the endometrium. Adhesion helps ensure that the blastocyst remains in the correct location and receives the nutrients it needs to grow.
3. Breaking through the epithelial barrier (epithelium and basement membrane): The blastocyst progresses towards the endometrial stroma.
4. Invasion: The embryonic trophoblast penetrates the stroma and invades the endometrial-myometrial vessels, replacing the endothelial cells. The blastocyst also begins to form the placenta at this stage.

This entire process is regulated and conditioned by a series of factors, both at the endometrial and embryonic levels.

What are the symptoms of embryo implantation?

In most cases, implantation is silent and does not produce any obvious symptoms. However, some women may notice certain subtle signs in the days following embryo transfer or ovulation.

🔴 Implantation bleeding

• This occurs in around 30% of women.
• It is light spotting (pink or light brown in colour).
• It usually lasts 1 to 3 days and is much lighter than menstruation.
• It can be confused with a period, especially in short cycles.

🤕 Pelvic pain or abdominal tightness

• Mild cramping or pressure in the lower abdomen.
• Similar to premenstrual pain, but less intense.
• It may be due to changes in the endometrium when receiving the embryo.

👙 Changes in vaginal discharge

• Thicker, white or creamy discharge.
• Related to increased progesterone.

🧠 Fatigue and mood swings

•     Some women notice increased sleepiness or tiredness.
•     There may also be emotional sensitivity or mild irritability.

👙 Breast tenderness

•     Breast swelling or discomfort, similar to premenstrual syndrome.
•     This is a hormonal response that may coincide with implantation.

It is important to note that these symptoms are not unique to implantation and may be similar to other normal hormonal changes in the menstrual cycle. The waiting period until the pregnancy test is a very important stage and each woman experiences it in a very different way. It is important to continue with your normal life, without obsessing over any changes you may notice, practising relaxation techniques and always maintaining a positive attitude.

How do you know if implantation has been successful?

There is no 100% sure way to know if implantation has occurred without a pregnancy test. However, if you notice any of the above symptoms about 7 to 10 days after ovulation or embryo transfer, it could be a positive sign.

📅 The pregnancy test should be done at least 12-14 days after ovulation or as directed by your specialist if you are undergoing assisted reproduction treatment.

Recommendations while waiting

• Avoid obsessing over every symptom.
• Maintain a normal life, without excessive stress.
• Practise relaxation or mindfulness techniques.
• Follow the instructions of your medical team.

Do you have any questions or need more information?

At Fertility Madrid, we specialise in treatments such as egg donation, in vitro fertilisation and artificial insemination, among others.
Please do not hesitate to contact our professionals at our fertility clinic and they will answer all your questions with no obligation.