Early Pregnancy

Early pregnancy or fertilization begins with the penetration of the female egg by a single male sperm, one out of the hundreds of millions that traveled up the female reproductive system. It is not completely understood how the minute sperm penetrates the firm capsule of the egg. Swimming in an indirect path, the sperm attacks the egg with the side of its head. Several sperm may begin to enter the outer egg capsule, but ultimately only one will enter the egg itself. Approximately 266 days later, a baby will be born

The egg and the sperm each bring to the union 23 chromosomes containing thousands of genes. This produces a new individual with 46 chromosomes, the correct number for a human being. It is this genetic material that determines sex, physical characteristics such as eye, hair, and skin color, body size and type, facial features, creativity, and, to a large extent, intellectual capabilities and even personality. After the sperm penetrates to the center of the egg, sperm and egg merge to become a one-cell embryo (zygote) and fertilization is complete. Multiple births result either from the fertilization of two or more eggs or from a single egg being fertilized and then splitting to form two or more embryos.

The next step in the process is cell division. Within 12 hours, the new cell has divided into two cells, which then become four cells, and so on, with the number of cells doubling every 12 hours. The new egg continues to make its way slowly down the fallopian tube to the uterus, regularly doubling its cell number and becoming not larger but more complex. Within 4 to 5 days after fertilization, the egg, by this time made up of 500 cells, reaches its destination inside the uterus. By the time the egg reaches the uterus, it has changed considerably from a solid mass of cells to a group of cells arranged around a fluid—filled cavity. This is called a blastocyst. One section of the blastocyst contains a compact mass of cells that will ultimately produce an embryo. The outer layer of cells, called the trophoblast, will produce the placenta, which provides nourishment. While all this has been taking place, the rest of the female reproductive system has not been idle. The ovaries have been secreting the hormone progesterone into the bloodstream. The result of this hormonal surge is a uterine lining that is swollen with blood, the perfect environment for implantation to take place.

Initially the egg does not dig deeply into the uterus. It clings to the surface of the uterus for a few days. Then the egg releases an enzyme that eats away at the lining of the uterus, allowing the egg to drop deeper into the lining, where it is surrounded by a pool of the mother's blood. Eight days have passed since fertilization took place. By the 12th day, the egg will be firmly embedded in its new home.

At this point, you are pregnant, although it is too early for you to have missed a period or to have any other symptoms of pregnancy. In the initial days and weeks after fertilization, miscarriage is common, often before a woman knows she was pregnant. In fact, an estimated 50 percent of fertilizations end in miscarriage.

The average time from fertilization to the birth of a baby is 266 days. Compared with the duration of gestation in most other species, that might seem an incredibly long time; when you consider the magnitude of this creation, it is a wonder it does not take longer. It is difficult to comprehend how something as complex as a human being can emerge from a single cell. What is equally perplexing is the seemingly effortless development of this microscopic speck. Every aspect of this process, from the creation of the smallest fingernail to the brain itself, is set into an exquisitely scripted timetable that rarely falters. If it does, the result can be a miscarriage or a birth defect. When you consider the magnitude of this creation, it is a wonder it does not take longer. It is difficult to comprehend how something as complex as a human being can emerge from a single cell

The two methods used to measure the duration of pregnancy are gestational age and fertilization age. Gestational age is measured from the first day of your last menstrual period, which is about 2 weeks before actual fertilization. Thus, a pregnancy calculated by this method is about 280 days (9.3 months). Fertilization age is measured from the time of fertilization. Thus, the duration of pregnancy calculated with this method is 2 weeks shorter than with the other method. Usually, obstetricians or family physicians calculate the duration of your pregnancy on the basis of gestational age.

Pregnancy Weeks 1- 40

Pregnancy Week 1 Pregnancy Week 2 Pregnancy Week 3 Pregnancy Week 4

Pregnancy Week 5 Pregnancy Week 6 Pregnancy Week 7
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Pregnancy Week 9 Pregnancy Week 10 Pregnancy Week 11 Pregnancy Week 12

Pregnancy Week 13 Pregnancy Week 14 Pregnancy Week 15 Pregnancy Week 16

Pregnancy Week 17 Pregnancy Week 18 Pregnancy Week 19 Pregnancy Week 20

Pregnancy Week 21 Pregnancy Week 22 Pregnancy Week 23 Pregnancy Week 24

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Pregnancy Week 29 Pregnancy Week 30 Pregnancy Week 31 Pregnancy Week 32

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