Prenatal Fetal Development

Week 1-2

• Woman’s first menstrual period.
• An egg is released from an ovary – more likely to conceive.

Week 3

• Sperm and egg meet in the fallopian tube.
• Conception occurs when the sperm enters the egg to form a zygote.
• The zygote travels down the fallopian tube for several days while dividing to form a blastocyst (ball of cells).
• The blastocyst becomes the embryo and develops into the baby.
• The outer group of cells of the blastocyst become membranes to nourish and protect the embryo.

Week 4

• The blastocyst reaches the uterus and buries into the uterine wall.

Week 5 – Embryonic Period

• The baby’s major systems and structures begin to develop.
• Cells multiply and start to take on specific functions (differentiate).
• Blood, kidney, and nerve cells develop.
• The central nervous system and heart begin to develop.
• The gastrointestinal tract starts to form.
• The baby’s external features begin to take form.
• The baby is most susceptible to birth defects.

Week 6-7

• Arms and leg buds start growing.
• Brain forms into 5 different areas.
• Eyes and ears form.
• Heart continues to grow and now beats a regular rhythm.
• Blood now pumps through the main blood vessels.

Week 8

• Arms and legs grow longer.
• Hands and feet begin to form.
• Brain continues to grow.
• Lungs start to form.

Week 9

• Elbows develop and toes can be seen.
• All essential organs have begun to grow.
• Nipples and hair follicles form.

Week 10

• Eyelids are more developed and can close.
• Ears take shape.
• Facial features become more distinct.
• The baby is no longer an embryo and is now a fetus.

Weeks 11-14

• Eyelids now close until about the 28th week.
• The face is well-formed.
• Nails and genitals appear.
• The liver begins making red blood cells.
• Hands can now make a fist.

Weeks 15-18

• Skin is almost transparent.
• Fine hair develops on the head.
• Muscles and bones keep developing.
• Movement and stretching begin.
• The liver and pancreas begin to produce secretions.

Weeks 19-21

• Baby can now hear.
• Baby is more active – moves and floats around.
• Mother can now feel the baby’s first movements.
• Baby can begin to swallow at the end of this period.

Week 22

• Eyebrows and lashes appear.
• Meconium is made in the intestinal tract.
• Baby’s heartbeat can now be heard with a stethoscope.

Weeks 23-25

• Bone marrow begins making red blood cells.
• Lower airways of the lungs develop.
• Fat storage begins.

Week 26

• The eyes are developed.
• The baby may startle in response to external loud noises.
• Footprints and fingerprints begin to form.
• Air sacs form in the lungs.

Weeks 27-30

• The brain grows rapidly.
• The nervous system controls some body functions.
• Eyelids can now open and close.
• Surfactant is produced in the lungs.

Weeks 31-34

• Baby gains a lot of fat.
• Rhythmic breathing occurs.
• Bones are fully developed.
• Storage of iron, calcium, and phosphorus begins.

Weeks 35-37

• Baby gains additional weight but remains relatively the same length.
• Sleeping patterns begin.
• Muscles, bones, and the heart are developed and complete.

Weeks 38-40

• Fingernails and hair continue to grow.
• Baby is due for birth.

References

Medline Plus. (n.d.). Fetal Development. Retrieved from https://medlineplus.gov/ency/article/002398.htm

 

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