Week 1 after conception: One sperm and one egg unite and create a single cell. This is called conception. Within 30 hours, the first cell splits and becomes 2 cells. By day 3, your 16-cell baby has traveled through the fallopian tube and settled into the uterus. By day 5 or 6, the baby is nestled into the lining of the uterus.
Week 2: Cells form a yolk sac and system to exchange food and oxygen between the baby and mother. It may be hard to picture, but at this early stage a baby looks like a flat disc.
Week 3: The flat disc of 2 layers becomes a disc with 3 layers.
Week 4: The disc folds over and looks more like a tube. Jaws are forming. Chambers form in what will be the heart. It begins to beat around day 25. Arms and legs start to develop.
Week 5: The head grows quite a bit as the brain develops. Arms keep growing and changing.
Week 6: Elbows, wrists and fingers begin to form. Eyes can be seen. The outer ear begins to take shape.
Week 7: Fingers keep developing.
Week 8: Fingers are formed but webbed. (A thin layer of tissue connects them.) Toes begin to form. The tail seen in the early stage is now gone. The head appears larger and measures half of the whole body. Eyelids are closed. Outer ears are formed.
Week 9: The head is about half the length of the body. By week 12, the body grows longer. Legs are still developing by week 12. Intestines are in the end of the umbilical cord until they move to the baby's belly in week 10. Sex organs are formed by week 12. By the end of that week, your baby is about 3½ inches long and weighs less than an ounce. He or she has a head, trunk and tiny limbs. Fingers and toes are tipped with soft nails.
Your provider is likely to suggest you continue your normal pattern. It depends on your present health and how active you were before you became pregnant. Before you start a prenatal exercise program, review our guidelines.
- Cystic fibrosis testing: You may choose to be tested to see if your baby has an increased chance of having cystic fibrosis (CF). Learn more about CF testing.
- First Trimester Screening: First Trimester Screening tells you what your risk of having a baby with Down Syndrome, Trisomy 18 or Trisomy 13.
Your moods are likely to change. Sometimes you will feel very happy. At other times you may feel worried or insecure. Changing body image, weight gain and clothes that no longer fit may cause mixed feelings. Concern for your baby being healthy may creep into your thoughts. You may dream of accidents and other dreadful events. These are all common. Expect them and do not let them worry you. Your body may also react in one or more of these ways:
- Feeling faint
- Lower abdominal pain
- Nausea and vomiting
- Pelvic pressure
- Vaginal spotting (light bleeding)