Understanding Fertilization: How Conception Happens and What Affects Fertility

In short: Fertilisation is the union of the sperm and the egg, the first step of pregnancy. The egg can be fertilised for only 12–24 hours, and fertility falls clearly as a woman gets older. Regular intercourse improves the chances, while smoking, pollution and excessive exercise reduce them.

Definition of Fertilization

Fertilization is the union of the male sperm with the female egg. Every month, during each menstrual cycle, a number of eggs begin to mature, and usually one egg fully matures and is released, becoming ready for fertilization. The egg matures inside a fluid-filled sac in the ovary called a Follicle. In the middle of the menstrual cycle, ovulation occurs when the follicle ruptures and releases the egg. The egg is then drawn into the first part of the fallopian tube, called the Fimbria, and begins moving along the tube toward the uterus.

Sperm Travels to the Egg

Sperm Reaches the Nucleus of the Egg

The egg remains capable of being fertilized for about 12–24 hours. If sperm enter the cervical canal and travel through the uterine cavity to reach the fallopian tube around the time of ovulation, one sperm may meet the egg. That sperm releases an enzyme that breaks down the egg’s outer layer, allowing it to enter the egg, where its genetic material joins with the egg’s genetic material. At this moment, the fertilized egg forms a protective covering that prevents any other sperm from entering. This fertilized egg, now called a Zygote, begins to divide as it continues traveling through the fallopian tube toward the uterus — a journey that takes around 3–4 days. The embryo then stays in the uterine cavity for another 2–3 days, developing into a blastocyst, before attaching to the uterine lining about 6–7 days after fertilization and beginning to grow. This process is known as Implantation.

Formation of the Zygote

Fertilization and Implantation of the Embryo

Factors Affecting Fertilization

1 - Age

Age affects fertility in both men and women. It helps explain why miscarriages become more common as a woman gets older, along with hormonal changes and uterine conditions such as fibroids. Overall fertility tends to decline gradually in women from the early thirties, and more noticeably after age 35. The impact of age on fertility is usually more gradual in men.

2 - Frequency of intercourse: Couples who have intercourse around 3 times a week have a higher chance of pregnancy compared with couples who have intercourse only once a week.

3 - Environment and daily habits: Certain modern-day factors — such as exposure to pollution, smoking, and excessive or very intense exercise — can affect the hormones (Gonadotropins FSH & LH) responsible for fertility in both men and women.

How can couples know if they are fertile, or if they may be facing difficulty conceiving?

For couples in their twenties having regular, unprotected intercourse, there is roughly a 25% chance of pregnancy each cycle. About eight to nine out of every ten couples will conceive naturally within a year, and about nine out of ten within two years.

A: It’s important to keep in mind that as couples get older — especially the wife — it becomes more important to move quickly with necessary fertility tests, particularly if there are signs such as irregular cycles, unusual hair growth patterns, a history of pelvic surgery that may have caused adhesions, or a known issue in the male partner such as undescended testicles.

B: Fertility investigations usually begin with a semen analysis for the male partner, which may need to be repeated more than once, along with confirmation of ovulation, an assessment of ovarian reserve (such as AMH), and a test of the fallopian tubes such as a hysterosalpingogram or contrast ultrasound. If these initial tests do not identify a clear cause, laparoscopy is not needed routinely, but it may be recommended when there are symptoms or signs of endometriosis or adhesions, and in these cases it can serve as both a diagnostic and therapeutic procedure.

What this examination involves is described step by step in our article on laparoscopy in gynecology.

C – It’s best for husband and wife to attend appointments together and to stay consistent with one specialist throughout treatment. Switching between multiple doctors in a short period can complicate the diagnostic process and may slow down progress toward finding a solution.

4 - Finally, it helps when both partners feel comfortable moving forward with testing. Many men feel embarrassed when asked to provide a semen analysis, worrying it reflects on their masculinity, while some women may feel similarly self-conscious about fertility testing. Open communication and good health awareness allow the physician to carry out the needed tests and provide the most appropriate care and guidance.

If you have concerns about fertility or would like guidance on next steps, the team at Dr. Najeeb Layyous clinic is available to discuss your situation and appropriate testing options.

Dr Najeeb Layyous

Obstétricien consultant, gynécologue et spécialiste de l’infertilité

F.R.C.O.G

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