Many changes take place in a woman's body during pregnancy.  By the time a woman misses her first period, her body has already been hard at work providing for her baby and preparing to nurture him or her until birth.

When conception takes place and a mother's egg is fertilized by a father's sperm, a unique human being comes into existence, equipped with its very own genetic code (DNA) that determines all of his or her physical characteristics from sex, hair and eye color to personality traits, likes and dislikes.  

In essence, from conception on, a baby is already essentially and uniquely the person he or she will be at 10,20, 30 or even 60 years old.

By the time a woman confirms that she is pregnant, usually at about 4-5 weeks, her baby is already 1/3 an inch tall, with a steadily beating heart and a rapidly developing brain and nervous system. 

Check out the following links to learn more about pregnancy testing and fetal development.