Fetal Development

FETAL DEVELOPMENT 

Pre-embryonic Period 

• First 2 weeks after conception

Embryonic Period 

• Beginning day 15 through approximately week 8 after conception 

Fetal period 

• Week 9 after conception to birth 

Week 1

• Blastocyst is free-floating. 

Week 2 to 3

• Embryo is 1.5 to 2 mm in length.
• Lung buds appear.
•  Blood circulation begins. 
• Heart is tubular and begins to beat.
• Neural plate becomes brain and spinal cord

Week 5

• Embryo is 0.4 to 0.5 cm in length.
• Embryo is 0.4 g.
• Double heart chambers are visible. 
• Heart is beating. 
• Limb buds form.

Week 8

• Embryo is 3 cm in length.
• Embryo is 2 g.
• Eyelids begin to fuse.
• Circulatory system through umbilical cord is well established. 
• Every organ system is present. 

Week 12

• Fetus is 6 to 9 cm in length. 
• Fetus is 19 g.
• Face is well-formed. 
• Limbs are long and slender.
• Kidneys begins to form urine.
• Spontaneous movement occurs.
• Heartbeat is detected by Doppler transducer between 10 and 12 weeks.
• Sex of fetus is visually recognizable. 

Week 16

• Fetus is 11.5 to 13.5 cm in length. 
• Fetus is 100 g.
• Active movement is present. 
• Fetal skin is transparent. 
• Lanugo hair begins to develop.
• Skeletal ossification occurs. 

Week 20

• Fetus is 16 to 18.5 cm in length. 
• Fetus is 300 g.
• Lanugo covers the entire body.
• Fetus has nails.
• Muscles are developed. 
• Enamel and dentin are depositing.
• Heartbeats is detected by regular (non-electronic) fetoscope.

Week 24

• Fetus is 23 cm length. 
• Fetus is 600 gm.
• Hair and head are well-formed. 
• Skin is reddish and wrinkled. 
• Reflex hand grasp functions are present. 
• Vernix caseosa covers entire body.
• Fetus has ability to hear.

Week 28

• Fetus is 27 cm in length. 
• Fetus is 1100 g.
• Limbs are well flexed.
• Brain is developing rapidly. 
• Eyelids open and close. 
• Lungs are developed sufficiently to provide gas exchange (lecithin forming ) If born,  neonate can breathe at this time.

Week 32

• Fetus is 31 cm length. 
• Fetus is 1800 to 2100 g.
• Bones are fully developed. 
• Subcutaneous fat has collected. 
• Lecithin-to-sphingomyelin (L/S) ratio is 12:1

Week 36

• Fetus is 35 cm in length. 
• Fetus is 2200 to 2900 g.
• Skin is pink and body is rounded. 
• Skin is less wrinkled. 
• Lanugo is disappearing. 
• L/S ratio is greater than 2:1

Week 40 

• Fetus is 40 cm in length. 
• Fetus is more than 3200 g.
• Skin is pinkish and smooth. 
• Lanugo is present on upper arms and shoulders. 
• Vernix caseosa decrease. 
• Fingernails extend beyond fingerprints. 
• Sole (plantar) crease run down to the heel.
• Labia majora are well developed.