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Fetal Development & Healthy Pregnancy Resources

The Facts of Life

A beautiful video from conception through the 9th month.

Fetal Development

Only a few weeks into pregnancy, a preborn child possesses the beginnings of every major essential organ and, by week eight, every organ is in place and growing.

Ultrasound technology now provides parents the opportunity to have “portraits” taken of their children as they grow in the womb. The images can be viewed by an ultrasound machine and show the child’s characteristics with striking detail. Fetal Development[1]

Conception

  • A zygote is formed when sperm and egg join. Twenty-three chromosomes from each parent also join to create the zygote with an entirely new, complete set of DNA. From the moment of conception, the zygote contains all of the genetic material necessary for the determination of any inherited characteristic.

Day 3 thru 4

  • The zygote travels down the fallopian tube to the uterus, and it rapidly divides into cells. At this point, it is called a blastocyst.

Day 5 thru 9

  • After the blastocyst attaches to the uterus, the uterine lining starts providing nourishment.

Week 2

  • The blastocyst splits into two sets of cells that form the placenta and the embryo.

First Trimester

Week 3

  • Brain, spinal cord, heart, and gastrointestinal tract begin to develop.

Weeks 4 and 5

  • The preborn baby is about ¼ inch long.
  • The heart pumps blood with a regular rhythm of between 105 and 121 beats per minute[2]
  • Brain waves can be detected.
  • The vertebrae and muscles begin to form throughout the body.
  • Arm and leg buds are beginning to grow from the body.
  • The preborn baby now possesses the beginning forms of every essential organ.

Week 6

  • The brain begins to control muscles and organs; both lungs begin to form.
  • Hands and feet begin to move.[3]
  • The preborn baby may begin moving around in the womb this week.

Week 7

  • The jaws, teeth buds, tongue, hair, and nipples begin to form.
  • As the trunk straightens, the elbows and toes become more visible.

Week 8

  • Every organ is in place and bones begin to harden.
  • The muscles can contract.
  • External features of the ear begin to take their final shape.
  • The preborn baby sighs, stretches, moves the head and tongue, and sucks the thumb.[4]

Weeks 9 through 12

  • The preborn baby’s face now has a fully human profile.
  • The preborn baby can turn his head.
  • The liver begins to produce blood cells.
  • Sex is well differentiated.
  • The preborn baby can make a fist and fingernails begin to form.
  • Eyelids close, not to open until Week 28.

Second Trimester

Weeks 13 through 16

  • The preborn baby is now about six inches long.
  • Facial muscle growth now makes expressions possible.
  • Fine hair called lanugo begins to grow on the head.
  • The preborn baby begins to suck and swallow amniotic fluid.
  • Sweat glands develop.
  • The liver and pancreas produce fluid secretions.

Weeks 17 through 20

  • The preborn baby is about eight inches long.
  • The heartbeat is now audible through a stethoscope.
  • Ears are developed and hearing begins for the first time.
  • The preborn baby becomes more active with increased muscle development.

Weeks 21 through 23

  • All the components of the eyes are developed.
  • Fingerprints and footprints are starting to form.
  • The skin becomes less transparent as fat begins to deposit.

Week 24

  • Air sacks are forming in the lungs.
  • Eyebrows and eyelashes are well formed.
  • The preborn baby has startle reflexes.

Weeks 25 through 28

  • The nervous system begins to take control of some body function.
  • The lungs are immature, but rhythmic breathing begins.
  • The eyes are wide open and the preborn baby blinks.
  • Hands are fully developed.

Third Trimester

Weeks 29 through 32

  • The preborn baby is 15-17 inches long and weighs over 4 pounds.
  • All bones are fully developed, though still pliable.
  • While lungs are still forming, the preborn baby begins to practice breathing.
  • Preparation for birth begins as the preborn baby shifts to a head-down position.
  • The preborn baby stores its own calcium, iron, and phosphorus and begins to gain weight rapidly.

Weeks 33 through 36

  • The preborn baby is 16-19 inches long and weighs between 5 ¾ pounds and 6 ¾ pounds.
  • Toenails reach the end of the preborn baby’s toes.
  • The preborn baby’s head has dropped into the pelvis.
  • Antibodies increase.
  • At week 35, or full term, the organs are ready to function on their own.

Weeks 37 through 40

  • The preborn baby weighs six to nine pounds and is fully capable of surviving outside the womb.
  • The preborn baby now fills the entire uterus and fetal movement decreases.
  • Breast buds are present in both sexes.
  • The lungs are maturing up to the day of delivery.
  • All other organs are fully developed.

© October 2011 Center for Arizona Policy, Inc. All rights reserved.


[1] Information throughout taken from the following sources: MedlinePlus Medical Encyclopedia: Fetal Development, National Institutes of Health (2009), www.nlm.nih.gov/medlineplus/ency/article/002398.htm (last visited Dec. 1, 2011);
Fetal Development, American Pregnancy Association (2007), www.americanpregnancy.org/duringpregnancy/fetaldevelopment1.htm (last visited Dec. 1, 2011);
Fetal development, Mayo Clinic (2011), www.mayoclinic.com/health/prenatal-care/PR00112 (last visited Dec. 1, 2011);
Interactive Prenatal Development Timeline, The Endowment for Human Development, www.ehd.org/science_main.php?level=i (last visited Dec. 1, 2011).