How does Natural Conception Occur?

Conception refers to the timely fertilization of the egg with the sperm leading to pregnancy. Here’s a brief description of what exactly happens in the body when a woman conceives naturally (or, when she doesn’t).

Process of Egg Maturation and Ovulation

• The reproductive system of a woman consists of two ovaries, which hold all her eggs. Each ovary connects to a fallopian tube by finger-like structures called the fimbriae, and each fallopian tube is attached to the uterus. 
• During every monthly menstrual cycle, a group of immature eggs in the ovaries start developing into follicles. Follicles are fluid-filled sacs that surround the eggs and gradually mature over two to three weeks.     
• Out of a group of mature follicles containing the mature eggs, only one egg, from any one of the ovaries, erupts from its follicular casing every month in a process called ovulation and moves into the fallopian tube with the help of fimbriae. 
• Ovulation occurs about 12-14 days after the last period. Sexual intercourse only around this time of the month can result in pregnancy. 
• In contrast, for fertility treatments such as IVF, one of the key points of difference is that a woman is given multiple injections to stimulate the ovaries to produce multiple mature follicles, which are then extracted for IVF.

Fig. 1: Egg Maturation and Ovulation

Source: flexbooks.ck12.org

Effects of Hormones on the Inner Wall of the Uterus.

Meanwhile, the ruptured follicle that remains after ovulation develops into a structure called the corpus luteum, which releases a  hormone called progesterone. It helps in thickening the inner wall of the uterus and causes the development of various blood vessels (in a process called vascularization), thus, making the uterine wall ready for attachment or implantation of the embryo or the fertilized egg.

Fig.2 : Effect of Hormones on the inner wall of the uterus.

Source: inviTRA

How does Fertilization Occur?

• After ovulation, the egg is viable for fertilization in the fallopian tube for about 24-36 hours only. 
• Sperm, once in the female reproductive tract, can survive for about 5 days. If unprotected sexual intercourse occurs around this time (just before, after, or,  during ovulation), the sperm travels through the vagina, cervix, and uterus, and makes its way into the fallopian tube. 
• Out of the 200-500 million sperm that are normally present in one ejaculation, only one can fertilize the egg. 
• Once the egg is fertilized by a single sperm, the egg blocks out the rest of the sperm cells, by hardening its outer layer called the zona pellucida. The excess sperm cells eventually die.

Fig. 3: Fertilization in the Fallopian Tube

Implantation of the Fertilized Egg

• The fertilized egg takes around four to six days to travel along the fallopian tube and into the uterus. 
• During this time, it is constantly dividing and reaches the blastocyst (around 100-150 cells) stage. 
• Once it enters the uterus, it exits the zona pellucida in a process known as ‘zona hatching’, and attaches itself, in a process known as implantation, to the thick uterine wall that has been richly vascularized. A mucus plug forms at the mouth of the cervix and stays in place until the end of pregnancy.                         
• The point of attachment of the fetus to the uterine wall is known as the placenta.

One of the functions of the placenta among many others is to secrete a hormone called Human Chorionic Gonadotropin (hCG) whose detection in the blood and urine forms the basis of a pregnancy test. The placenta also secretes hormones that prevent the disintegration of the endometrium (inner wall of the uterus).

    

Fig. 4: Implantation

Source: drze.de

To summarize the above processes,

Successful pregnancy can occur only when all of the following steps occur successfully:

1. Transport of a healthy egg into the fallopian tube after ovulation.
2. Transport of the sperm to the fallopian tube after copulation.
3. Fertilization of the egg with the sperm in the fallopian tube
4. Implantation of the embryo on the inner uterine wall.

If any of the above steps do not occur successfully, pregnancy does not transpire. Problems with ovulation, fallopian tubes, sperm quality, and hormonal imbalances are the leading causes of infertility in males and females.

If you have any doubts or further questions regarding the above process, get a free consultation from the best fertility doctors in Bangalore with Ferticare.
Visit us at www.ferticare.in to book a free consultation today!