Sperm are small cells produced in the testes of males. These sperm mix with various fluids in the male reproductive system and are released from the penis during ejaculation. The semen released during ejaculation contains millions of sperm. However, for conception to occur, only one sperm is needed.

Eggs reside within the ovaries. Hormones that regulate a woman's menstrual cycle cause one or two eggs to mature each month. This means the eggs reach a state suitable for fertilization. During this time, the hormones of the menstrual cycle also prepare the uterine lining by thickening it to support the implantation of a fertilized egg.

Around the middle of the menstrual cycle, the matured egg is released from the ovary. This process is known as ovulation. Once released, the egg is guided into the fallopian tube by small fibers located at the end of the tube. The egg then travels along the fallopian tube toward the uterus.

Once outside the ovary, the egg spends 12-24 hours in the fallopian tube and uterus, checking for the presence of sperm to enable fertilization.

If semen enters the vaginal canal, the sperm within it can travel through the cervix into the uterus. The sperm work in cooperation with the uterus to travel to the fallopian tube. If both the egg and sperm reach the fallopian tube at the same time, the sperm will swim inside the egg. This is referred to as fertilization. Sperm can survive for about 5 days while searching for an egg to fertilize. Fertilization does not occur immediately.

From the time semen enters the vaginal canal (which most often happens during sexual intercourse, though it can also occur in cases of sexual assault), sperm can stay in the uterus and fallopian tube for up to 5 days. Therefore, there is a possibility that the time between sexual intercourse and fertilization can extend up to 5 days.

The fertilized egg travels through the fallopian tube towards the uterus. It breaks down into smaller cells and forms a cell mass. It may take about 3 to 4 days for this cell mass to reach the uterus. Over the next 2 to 3 days, as this cell mass remains within the uterus, it attaches to the uterine wall, leading to pregnancy. The cells inside the cell mass start developing into the embryo. The outer layer of the cell mass forms the placenta. At this stage, the body starts producing pregnancy hormones, which prevent the shedding of the uterine lining. This is why menstruation stops during pregnancy.

In cases where an egg and sperm do not meet, or if the fertilized egg becomes a cell mass but does not implant in the uterine wall, the thickened uterine lining may shed and exit the body through the vaginal canal. This is known as menstruation.

Natural pregnancy occurs through vaginal intercourse. However, couples who cannot conceive naturally can seek modern reproductive services such as in vitro fertilization (IVF). However, these services are expensive. Even if one wishes to become a parent but is unable to conceive, the law allows for the possibility of adopting a child.