Understanding Postovulatory Phase, Fertilization, and Childbirth

Postovulatory Phase and Fertilization

The postovulatory phase comprises days 15 to 28 of the menstrual cycle. After the expulsion of the ovum, the follicle degenerates, fat accumulates, and it becomes the corpus luteum. The innermost layer of the uterus gradually thickens and acquires a spongy appearance with numerous glands and blood vessels to nourish a future embryo. If fertilization does not occur, around the 28th day, the thickened layer of the uterus, the endometrium, is destroyed and expelled, along with the remains of the unfertilized egg. This process produces a hemorrhage known as menstruation or a period.

If fertilization occurs, the innermost layer of the uterus remains swollen during pregnancy. The corpus luteum in the ovary continues to produce hormones to support the fetus, and menstrual cycles stop until after delivery.

Fertilization is the union of an egg and sperm. The sperm penetrates the thick layer that protects the egg. The merger of the two nuclei gives rise to a zygote, which is the first cell of the embryo.

Implantation and Early Development

As the zygote passes from the fallopian tube toward the uterus, it begins to divide by mitosis, doubling the number of cells. Approximately 7 or 8 days after fertilization, the embryo implants in the uterine wall. From the third month, the embryo is called a fetus.

Exchanges Between Mother and Fetus

In early pregnancy, structures develop to protect the embryo, supply nutrients, and remove waste products. These organs include:

• The amniotic membrane: Forms the amniotic cavity in which the embryo is suspended.
• Amniotic cavity: Contains the amniotic fluid that bathes and protects the embryo from shocks.
• The placenta: An organ that connects the embryo to the uterine wall of the mother through the umbilical cord.

The placenta allows oxygen and nutrients to reach the embryo while simultaneously collecting waste products such as CO2 and urea. The placenta acts as a barrier, preventing the flow of cells and harmful substances. However, other substances such as alcohol, nicotine, some drugs, and certain viruses can cross the placenta and harm the fetus.

Childbirth

Childbirth is the process of the fetus being expelled from the uterus. It typically occurs after 40 weeks of gestation and happens in several stages:

1. Dilation of the cervix: Uterine contractions begin, facilitating the dilation of the cervix, which must open to about 10 cm. During this time, the amniotic sac ruptures, releasing the amniotic fluid (often referred to as "breaking water").
2. Fetal expulsion: Contractions of the uterus become more intense and prolonged. With the mother's effort, the fetus is pushed out through the vagina. Once the fetus is delivered, the umbilical cord is cut.
3. Delivery of the placenta: Approximately 15 minutes after birth, the uterus expels the placenta.

Contraception

Contraception aims to prevent fertilization during sexual relations.

• Condoms: Very suitable for casual sex, offering double protection: contraception and prevention of sexually transmitted diseases.
• Birth control pills: Contain female hormones that prevent ovulation. If ovulation does not occur, pregnancy cannot happen. They must be taken daily. There are also patches, implants, and vaginal rings that serve a similar purpose.
• IUD (Intrauterine Device): A small plastic and metal object placed in the uterus to prevent implantation of the zygote. It should be placed by a physician and can remain in the uterus for 3 to 4 years.
• Diaphragm: A rubber disk placed at the bottom of the vagina to cover the cervix and prevent sperm entry.
• Spermicides: Creams, gels, and foams containing chemical substances that destroy sperm.
• Surgical methods: Tubal ligation (for women) and vasectomy (for men) are surgical operations that prevent the passage of ova or sperm. These are permanent and irreversible methods.