There are three main stages of fetal development that occur during the nine months of a pregnancy; these are conception, embryonic development and fetal development. The actual time for gestation of a human baby is 40 weeks, but most people seem to prefer to use the term ‘nine months’.

Conception occurs two weeks into the woman’s monthly menstrual cycle. The uterus is prepared for a possible pregnancy by increasing the blood flow to the endometrium or the lining of the uterus. When an egg is fertilized, it makes its way down the fallopian tube to the uterus, where it implants into the wall and begins to grow. This is the moment when conception is considered to have occurred.

Embryonic development is the second stage of the pregnancy and the most critical. It takes place from conception up to 11 weeks. As the cells divide and re-divide, important foundations and functions are being laid down.

By the fourth week, there is a differentiation between the embryo that will be the baby and the placenta. By the sixth week the heart is beating and the limbs are starting to develop. By the eighth week, the teeth are growing in the gums and the intestines are forming. By the eleventh week, the embryo has joints, eyes, major organs and central nervous system all starting to develop.

Fetal development: from the twelfth week, the embryo is referred to as the fetus and genital development helps to distinguish it as a boy or a girl. Up to the sixteenth week, the nails, hair and vocal chords are developed and the kidneys and liver begin to function properly. The bones have been soft like cartilage to this point, but now they begin to harden.

Between the sixteenth and the twentieth weeks there is a rapid growth spurt and fat is formed under the skin. The heart is pumping strongly, sending twenty-five quarts of blood around the little body. Waste products start to accumulate in the fetus’ bowel. The fetus spends time awake and asleep and hiccoughs quite regularly.

After this growth spurt, development of the fetus slows down for the next four weeks. Eyelids and eyebrows are formed, and, in boy babies, the testes descend from the pelvis. At twenty-four weeks, the average weight of the fetus is 1.3 pounds or .6 kgs.

The lungs develop during the next four weeks, from the twenty-fifth to the twenty-eighth week, which is why babies born prematurely at twenty-eight weeks or later will generally survive. This period is also a time of rapid brain development; the nostrils and eyes open and ligaments around the joints form.

From the twenty-ninth week until birth, around the fortieth week, the lungs become fully developed and all the major organs and body systems, including the immune system, complete their development. The fetus puts on weight during these final weeks, getting ready to survive outside the uterus. During the final three weeks there is rapid weight gain, at the rate of one ounce or 28.35 gms each day.

Birth will occur sometime around the fortieth week of the pregnancy and the process is complete.