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Pregnancy Weeks 0-12 - Page 2

Healthy Pregnancy Newsletter
Healthy Pregnancy Newsletter - Growing Baby

Amazing changes are occurring inside your body during these first weeks of pregnancy. Once the fertilized egg reaches the uterus and implants, all the major body organs and systems begin forming and developing at an incredible rate. Your unborn baby is first called an embryo until the eighth week, when he or she is called a fetus. In these early days of pregnancy, three important and unique systems develop to nourish and protect your unborn baby:

  • Amniotic sac. This is a sac filled with amniotic fluid that surrounds the fetus throughout the pregnancy. The amniotic fluid is liquid made by the fetus. The amnion is a membrane that covers the fetal side of the placenta. The amniotic sac and fluid protect the fetus from injury and help regulate temperature inside the uterus (womb).
  • Placenta. The placenta is an organ shaped like a flat cake that only grows during pregnancy. The placenta attaches to the uterine wall with tiny projections called villi. Fetal blood vessels grow from the umbilical cord into these villi, exchanging nourishment and waste products with the mother's blood.
  • Umbilical cord. This is a rope-like cord connecting the fetus to the placenta. The umbilical cord contains two arteries and a vein, which carry oxygen and nutrients to the fetus and waste products away from the fetus.

Your unborn baby's growth and development is amazing in the first trimester. Here's a look at what happens week by week during this time:

By the end of 4 weeks

  • Major systems and organs begin to form
  • Embryo looks like a tadpole
  • Neural tube (which becomes the brain and spinal cord), digestive system, and heart and circulatory systems begin to form
  • Beginnings of the eyes and ears are developing
  • Tiny limb buds appear (which will develop into arms and legs)
  • Heart is beating

By the end of 8 weeks

  • Major body systems continue to develop and function, including the circulatory, nervous, digestive, and urinary systems
  • Embryo is taking on a human shape, although the head is larger in proportion to the rest of the body
  • Mouth is developing tooth buds (which will become baby teeth)
  • Eyes, nose, mouth, and ears are becoming more distinct
  • Arms and legs are clearly visible
  • Fingers and toes are still webbed but can be clearly distinguished
  • Main organs continue to develop and you can hear the heartbeat using an instrument called a Doppler
  • Bones begin to develop and the nose and jaws are rapidly developing
  • Embryo is in constant motion but cannot be felt by the mother

After eight weeks, the embryo is referred to as a fetus (which means offspring). Although the fetus is only 1 to 1 1/2 inches long at this point, all major organs and systems have been formed.

During weeks 9-12

  • External genital organs are developed
  • Fingernails and toenails appear
  • Eyelids are formed
  • Fetal movement increases
  • Arms and legs are fully formed
  • Voice box (larynx) begins to form in the trachea


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