Fertilization usually takes place in the fallopian tube. Only one of the millions of sperm will pass through the membrane of the ovum (female egg) achieving conception. Once the sperm has fertilized the ovum, enzymes in the egg alter the inner membrane and make it impossible for more sperm to enter. Once introduced, the nuclei of the sperm and the egg, each containing 23 chromosomes, unite to form one fertilized egg with the 46 chromosomes needed for human development. The whole process of intermingling takes 24 hours. The fertilized egg then travels to the womb where it embeds itself like a seed in the lining of the uterus and begins to grow.

Physical Changes in the Mother During Pregnancy
During the first trimester, the uterus, a small, hard, pear-shaped organ becomes a soft, spherical sac through which the baby can be easily felt. By the end of the first trimester, the uterus has expanded out from the pelvic cavity and touches the abdominal wall. It continues to grow and, at term, the uterus is between 500 and 1,000 times its prepregnant size. The actual growth of muscle fibers, not just the stretching of the uterus, is responsible for most of the increase in size. At the end of the ninth month, the uterus almost touches the mother’s liver just under the lower right rib.

The prepregnant cervix is firm and muscular. During pregnancy, from as early as the first trimester, the cervix begins to soften, caused by an increase in the number of blood vessels and mucus glands in the cervical lining. The cervix also becomes spongy in texture and creates a mucous plug that seals the cervical opening soon after fertilization takes place. This plug is released some time around the start of labor.

Soon after conception, the vagina experiences an increase in blood flow and as a result it takes on a violet hue. Throughout pregnancy, the vaginal wall thickens, elongates, and becomes looser and more elastic in order to prepare for the enormous amount of stretching that it will go through during the delivery. The opening to the vagina and the vulva become swollen and vaginal discharge becomes thick, white, and acidic, which helps guard against infection.

Within a couple of weeks of conception, the breasts can feel full, heavy, and sore. These sensations are due to the enlargement of ducts and lobules known as alveoli. During the first trimester, the breasts begin to increase in size. As time progresses, the areola, the pigmented area around the nipples, become wider and darker and the nipples themselves become larger and darker. After the first trimester, some women may notice a slight discharge of colostrum, a highly nutritious, yellowish liquid that the newborn suckles on until the milk comes in, around the third day after birth.

How to Have a Healthy Pregnancy
Although each individual responds to pregnancy differently, and there is no such thing as a perfect pregnancy, there are many ways to contribute to a healthy one. “Probably most important is that the woman realizes the physiological impact carrying a child has on her health and that she listens to her body’s needs,” says Dr. Linton. “Adequate rest, including naps, ‘mental’ breaks, and sufficient sleep, is essential. Maintaining a positive outlook and keeping stress to a minimum are beneficial to both mother and baby.