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Stages of Pregnancy - First 12 Weeks

This is an exciting time. Your baby begins as a fertilized egg about the size of this dot.

Your first prenatal visit: You should be seen in the clinic during your first 3 months. The first visit lasts longer than others. A nurse will take a detailed medical history. Your doctor or nurse midwife will give you a complete physical with a pelvic exam and a Pap smear. These visits may occur on the same day or two different days. Some lab tests may also be done.

Your estimated due date is based on exam results and the date of your last period. If your periods come every 28-30 days, the math is simple. Just take the date of the first day of your last period and add 9 months and 7 days. For example: If your last period started on Jan. 1, your baby would be due around Oct. 8. About 5 percent of women have their babies on their due date. Most give birth within 2 weeks before and 2 weeks after that date.

Early development

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.

Changes in you

Weeks 1-4

  • You may notice darker skin over your nipples or a line of darker skin down the center of your lower abdomen.
  • You may need to pass urine more often.
  • It is normal to feel tired even if you eat a balanced diet with plenty of iron. Fatigue is caused by extra hormones. The placenta produces more estrogen and progesterone to thicken the lining of the uterus. This is where the fertilized egg is attached and nurtured in the weeks ahead.

Weeks 5-8

  • Your blood volume rises to help meet the baby’s needs.
  • Breasts are likely to be tender.
  • You have gained about 1-1½ pounds.
  • Your uterus is about the size of a tennis ball.

Weeks 9-12

  • Your uterus is now about the size of an orange.
  • Normal clothes may be too snug for your growing stomach and breasts. It may be time for a larger bra and pants with stretchy panels.
  • By the end of week 12, you will have gained 3-4 pounds.

Activities & screenings

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.

Possible concerns - first trimester

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:

  • Constipation
  • Feeling faint
  • Fatigue
  • Gas
  • Headaches
  • Lower abdominal pain
  • Nausea and vomiting
  • Pelvic pressure
  • Vaginal spotting (light bleeding)
Love + Medicine

Every day, Gundersen Health System delivers great medicine plus a little something extra—we call it Love + Medicine.

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