Around the fourth week and third day of pregnancy, the baby implants itself into the uterus inside the endometrium. In the endometrium, the baby begins to produce human chorionic gonadotropin, which maintains the uterine lining. In turn, the ovary is signaled to stop releasing the egg for menstruation.
The baby is about ¼ inch long, which is about the size of a grain of rice. The baby's face has taken form, and the baby's eyes appear to be dark circles. During this time, tiny buds that will develop into limbs can be seen.
Some women experience some spotting and cramping when implantation takes place. Women often feel tired or nauseous during this phase of their pregnancy. Many of the symptoms they experience are similar to PMS.
The placenta develops at this time, which provides nourishment to the baby during the pregnancy.