Fetal development describes the scientific process of growth and development of the unborn from a single, fertilized egg to birth. ¹

Fertilization:  Day 1:  Life Begins

• Life begins when the sperm and ovum (mature egg) unite to form a single cell (zygote, or fertilized egg)¹.
• 23 chromosomes are from the male and
• 23 chromosomes are from the female.
• The combined 46 chromosomes are now a zygote.
• This zygote is unique.
• It is a cell which never existed before.
• This cell has the genetic blueprint for eye color, gender, intelligence, height, hair color, skin tone, facial features, body type and personality characteristics.

• THE EMBRYO:  3-5 days after fertilization, the zygote becomes an embryo.
  • The embryo travels down the fallopian tube and
  • enters the uterus to implant into the uterine wall.

Week 2 – Embryo Growth

• The embryo implants into the uterine wall by the seventh day.
• The embryo begins to draw nutrients.
• Now hormones prevent the menstrual period (for most pregnant women).

Week 3 – Embryo Growth

• The brain, spinal cord, and nervous system begin to develop.
• The growing backbone causes the body to curl.
• The beginning of future organs are visible.
• The heart is formed.
• The heart beats around day 20.

Week 4 – Embryo Growth

• Simple kidneys, liver, and digestive system form.
• Arms, legs, eyes, and ears form.
• At 28 days old, this embryo is 10,000 times larger than the original fertilized egg.

Month 2 (Week 8) The Fetus

• The beating heart is visible on an ultrasound monitor.
• Brain waves can be recorded as early as 40 days.
• Impulses begin to control and regulate circulation, digestion, and waste elimination.
• Facial features are beginning to form: eyes, ears, lips, tongue.
• The jaw forms, including 20 tiny tooth buds in the gums.
• The eyelids seal to protect the light-sensitive eyes.
• At 8 weeks the embryo becomes a fetus (Latin word meaning “Young one.”)
• Elbows and fingers are now evident.
• The fetus is a half an inch in length.
• Everything is now present that will be found in a fully-formed and developed adult. 
  • The heart has been beating for more than a month.
  • Immature lungs, kidneys, liver, brain, nervous system and digestive system are present.
  • Forty muscle sets have begun to operate in conjunction with the nervous system.
  • The fetus is capable of responding to touch.

Month 3  (Week 12)  Fetal Growth

• The fetus is an average length of 2 inches.
• The soft, bony limb tissue now begins to calcify.
• The fetus has a routine: sleeps, wakes, exercises.
• Other developments:
  • Curls its toes
  • Turns its head
  • Opens and closes its mouth
  • “Breathes” amniotic fluid
  • The iris of the eye is developing.
  • Fingers and toes are forming, and fingernails begin to appear.
  • The fetus has fingerprints, a unique identity that will identify him or her for the rest of its life.
  • The fetus will move away if touched.
  • Grasps fingers around an object
  • If the palm is stroked, the fetus will make a tight fist.
  • The fetus is able to experience pain.
  • Sexual differentiation is apparent.
  • All organic systems are functioning.
  • The fetus has skeletal structure, nerves, and circulation.
  • The fetus can now yawn and suck.
  • The fetus can cry, and tries to do this in the uterus at times.

Month 4  (Week 16) 

• The heart is beating.  (It pumps 25 quarts of blood a day.)
• The ears are functioning.
• There is strong evidence that the fetus can hear quite a bit, including its mother’s voice and her heartbeat.
• The pregnant woman reports feeling movement within.
• The fetus is nourished an hour or two after the mother eats.
• The fetus can now urinate and swallow.
• By the end of this month the fetus is 7 inches in length.
• At 16 weeks the gender of the fetus can be seen on ultrasound.

Month 5 (20 Weeks) “Quickening”

• The fetus is approximately 12 inches long and weighs approximately one and a half pounds.
• The fetus curls when the mother moves and stretches out when the mother rests.
• Some pregnant women report being able to feel and sense this movement.
• Fetal movement felt by the pregnant women is called “quickening.”
• The female fetus now has a uterus and ovaries containing eggs.
• Loud noises may startle the fetus and cause him or her to jump in response.
• At this point the fetus rests when the mother rests.
• This is the halfway point of pregnancy.

Month 6  (Week 24)

• Vernix (white, waxy ointment) covers the fetus’ skin as protection.
• The skin is pink, translucent and wrinkly.
• Rapid eye movements are noted.
• The fetus has a blink-startle response if stimulated by loud noises.
• If born now (prematurely), and given the proper care, survival is possible.
• The lungs are well-developed and nearly ready to work.
• Hair is now visible.
• Unborn males have testicles which are ready to descend from the abdomen to the scrotum.
• From week 22 to week 32, the fetus experiences pain more intensely than at any other time in development.
• At 24 weeks, the fetus weighs slightly more than a pound.

Month 7 (Week 28)

• Hearing, vision, taste, and touch are in process.
• Eyelashes are clearly visible and the eyes begin to open.
• The fetus has fully-functioning taste buds on her or his tongue.
• Now the fetus can experience motion and do flips in the womb.
• The fetus can suck its thumb.
• The fetus now weighs approximately 3 pounds and is approximately 11 inches in length.
• If born at this age, the fetus can breathe air on its own.
• The brain is developed enough to coordinate rhythmic breathing and regulate its body temperature.
• Pregnant women report Braxton-Hicks Contractions at this point.  These contractions occur in the third trimester (month 6-9 or weeks 24-36) and prepare the pregnant woman for childbirth.

Month 8 (Week 32)

• The fetus’ skin thickens and stores a layer of fat for insulation and nourishment.
• Antibodies form to give protection from disease and give immunity.
• The heart is now pumping 300 gallons of blood a day.
• The fetus absorbs a gallon of amniotic fluid per day and completely replaces that fluid every three hours.
• The fetus now has definite, active cycles of sleep and wakefulness.

Month 9 (Week 36 weeks to Week 40)

• The fetus is now 20 inches in length.
• Its body is more plump.
• The fetus has a firm grasp.
• Approximately one week before the 260th day, the fetus stops growing and drops its head downward into the pregnant mother’s pelvic cavity, preparing for birth.
• The average pregnancy is 280 days from the first day of the pregnant woman’s last period.
• Most babies are born between 266 and 294 days.
• They weigh between 6 and 9 pounds.
• The fetus is capable of living outside of the womb.

 

Related topic:

See: Images of Early Development

Footnotes:

¹ https://www.webmd.com/baby/guide/understanding-conception