• Print Print
  • Share
  • Text Size: A | A | A


Pregnancy lasts 40 weeks, beginning from the first day of your last menstrual cycle and is broken into groups to form three trimesters.

Learn what you and your baby will experience over the next nine months.

First trimester: week 1 – week 12

8 Week Ultrasound at Birthing Center at Providence St. Joseph Medical CenterDuring this time your hormone levels and body change, affecting the entire organ system. It is common to feel tired and experience morning sickness. During the next 12 weeks you may need to make adjustments, such as going to bed earlier and eating smaller but more frequent meals.

Embryonic Period: weeks 4-8

Embryos are vulnerable to environmental damages that can cause birth defects. For example:

  • Radiation
  • Drugs
  • German measles
  • Teratogens
  • Infections

Week 4: Baby is officially an embryo the size of a poppy seed

  • ¼ inch long
  • Embryo has a head and visible tail
  • Eyes and ears are developing
  • Voice box and swallowing mechanism develop
  • Heart is beating
  • Nervous and circulatory systems are laid down
  • Digestive tract begins to form

Week 5: Baby looks more like a tadpole than a human and is the size of a sesame seed

  • Internal organs forming: lungs, liver and kidneys
  • Arm and leg buds begin to form (arms develop faster than legs and feet)
  • Eyes are visible
  • Depressions for the nostrils are visible

Week 6: Baby is as long as a lentil

  • Most dramatic changes in the face occur
  • The main internal organs have finished forming
  • The heart fuses into four chambers

Week 7: Baby is nearly twice the size since previous week, about the size of a blueberry

  • Arms and leg buds grow rapidly into limbs
  • Fingers and toes start to develop
  • Nervous system is nearly fully formed
  • Muscle fibers begin to develop
  • Tail disappears

Week 8: Baby is about the size of a kidney bean

  • Bones begin to develop
  • Nose and upper jaw grow rapidly

Fetal Period: weeks 9–12

By the end of eight weeks the fetus is 1½ inches long. The head is extremely large compared to the body, 10 tooth buds are visible and ankles and wrists are formed. Fingers and toes are still webbed and muscles in the neck and trunk begin to contract, causing movement.

Weeks 9-12: Over the next few weeks the baby will grow from the size of a fig to the size of a lime

  • Fingernails and toenails develop
  • Eyelids are properly formed
  • Fetal movement increases
  • Limbs and internal organs are fully formed
  • Sex organs develop

Second trimester: week 13 – week 28

20 week Ultrasound at Birthing Center at Providence St. Joseph Medical CenterMany women find the second trimester easier than the first, experiencing less nausea and fatigue. During this time more noticeable changes begin as your stomach expands and the baby grows. It is common to have back, abdomen and groin aches as your body adjusts to your baby’s growth. By the end of the second trimester most women feel the baby move!

Weeks 13-16: Baby will grow from the size of a shrimp to the size of an avocado

  • Weighs six to eight ounces
  • Head is developed
  • Mouth, nose, eyes and outer ears are properly shaped
  • Skin is thin and red
  • Fingers and toes are fully separated
  • Feet and hands begin to develop ridges

Weeks 17-20: At 17 weeks the baby will be the weight of a turnip and by the end of 20 weeks will be as long as a banana

  • Weighs 12 ounces and is 10 inches long
  • Lanugo begins to cover the body (fine downy fuzz is replaced by hair follicles after birth)
  • Vernix covers the skin to protect it from becoming waterlogged
  • First movements can be felt by the mother (“quickening”)
  • External sex organs can be determined by ultrasound

Weeks 21-24: Over a few weeks the baby will grow to the size of an ear of corn and weigh as much as a large mango

  • Brain undergoes most important period of growth

Weeks 25-28: At 25 weeks the baby will be as long as an English Cucumber and equal the size of a Chinese cabbage by 28 weeks

  • Weighs 2.4 pounds and is 14 inches long
  • Hair is getting longer
  • Eyebrows and eyelashes are visible
  • Eyes open and shut
  • Fat develops under the skin and around organs

Third trimester: week 29 – end of pregnancy

35 week Ultrasound at Birthing Center at Providence St. Joseph Medical CenterIn 11 short weeks, you will give birth and welcome your new baby into the world! Many women experience similar discomforts as the second trimester. The baby is getting bigger and puts more pressure on internal organs, such as your bladder and stomach. Many women need to urinate more often and eat smaller and more frequent meals. These discomforts will subside after birth.

Weeks 29-32: Baby starts taking up more room in your uterus by growing to the size of a jicama and weighing as much as four oranges

  • Weighs 3 ½ pounds and is 16 inches long
  • Lungs and vital organs are still immature and developing
  • Male testes descend to the scrotum by week 32

Week 33-Birth: Nearly as long as a large leek and the weight of a small pumpkin, the baby bulks up and doesn’t have much room left in your uterus

  • At 34 weeks the baby weighs five ½ pounds and is 18 inches long
  • At term the baby weighs seven to nine pounds and is 20-23 inches long
  • Kidneys are fully mature and lungs are almost fully grown
  • Head and body are in proportion to each other
  • Iris is blue, permanent eye color will not appear until several days or weeks after birth
  • Most of the lanugo has disappeared
  • The vernix is still covering the skin, except around the mouth and eye area. It will be gradually absorbed by the skin and traces are usually still evident at birth