UNIT 2.0

TOPIC: PREGNANCY

Instructional Materials: 

Teaching Method:

Types of Assessment: 

Learning Objectives: At the end of the lesson the students will be able to;




2.0 Introduction

Pregnancy also known as gestation, is the duration which a woman bears one or more offspring’s as it develops inside her. Pregnancy usually occurs by sexual intercourse but may also results from assisted reproductive technology procedures. It typically takes a duration of 40 weeks from the last menstrual period to childbirth. A pregnancy may end up in a live birth, a spontaneous abortion, an induced abortion, or a still birth. Pregnancy is divided into 3 trimesters, each lasting approximately 3 months.


2.1 Definition of Pregnancy: 

Pregnancy is the state of carrying a developing embryo or fetus within the female body. It is indicated by the cessation of menses after fertilization has occurred. 

Pregnancy is a state of being with a child, from the conception to the expulsion of the fetus that normally takes a period of 280 days or 40 weeks from the last menstrual period.


2.2 Process of fertilization to pregnancy

After ovulation, the ovum passes into the uterine tube. It is propelled along the tube by the cilia and peristaltic muscular contraction of the tube. If not fertilized within 24-36hrs, the ova will degenerate. During intercourse about 200 million sperm cells per ml of semen are ejaculated into the vagina (posterior fornix). The sperm travels upward fast; those that reach the loose cervical mucus survive to propel themselves toward the uterine tube while the rest are destroyed by the acid medium of the vagina. More sperm dies on the way to the ovum, by the time they reach the uterine tube only few will survive. If the condition is favorable in the uterine tube, sperm may survive for up to 72hrs.

Only 1 sperm penetrates the ovum. An enzyme called hyaluronidase is released which allows the penetration of the zona pellucida and the cell membrane surrounding the ovum. The cell wall immediately hardens, preventing other sperm from entering, and the nuclei of the two cells fuse together to form the zygote. Both the sperm and ovum contribute half the complement of chromosomes each to make a total of 46.

After the formation of the Zygote which normally takes place in the ampulla of the uterine tube, it continues its journey to the uterus which takes about 3 or 4 days. During this time cell division takes place and the zygote divides into 2, then 4, 8, 16 and so on until a cluster of cells is form called the Morula. Then, a cavity filled with fluid is form known as the blastocyst. Surrounding the blastocyst is single layer of cells called the trophoblast while the remaining cells are clumped together at one end of the blastocyst forming the inner cell mass. The trophoblast later forms the placenta and the chorion, while the inner cell mass will become the fetus and amnion.

As these formations continue its journey to the uterus, it receives nourishment in form of glycogen from the goblet cells of the uterine tubes and later from the secretary glands of the uterus. In the uterus it lies free for another 2-3 days, and then the trophoblasts adheres to the endometrium and begin to secrete substances which digest the endomtrum cells allowing the blastocyst to become embedded. Once this happens the endometrium layer is known as the decidua.

The decidua is about 4 times thicker than the endometrium due to increase secretion of oestrogen. The corpus luteum also produces large amount of progesterone which stimulate the secretory activity of the endometrial gland and increase the size of the blood vessels. This accounts for the soft, vascular, spongy bed in which the fertilized ovum implants