Fetus Development Information

The stage of prebirth development from nine weeks of gestation to birth. The organ systems and major structures take form during the embryo stage, which encompasses the second to the eighth weeks of gestation.

During the fetal stage, which is 32 weeks in a full-term pregnancy, the systems, organs, and structures grow and develop further sophistication in preparation for independent life. The fetus reaches viability (possibility of surviving on its own) at around 24 weeks of gestation.

Fetal Age (Gestational Weeks)Fetal SizeKey Developments
143 inches in lengthface clearly formed
liver produces erythrocytes
186 inches in lengthlanugo (fine hair) on head
movement may be detectable
gastrointestinal tract produces meconium
2411 inches in length
one pound in weight
viability possible with intensive medical care
movement apparent
eyebrows and eyelashes
fingerprints and footprints
heartbeat detectable with stethoscope
gender detectable with ultrasound
startle reflex
2815 inches in length
two to three pounds in weight
viability possible
eyelids open and close
increasing level of brain and nervous system functions
alveoli in lungs
3217 inches in length
four pounds in weight
viability probable
body fat
breathing movements in lungs
3619 inches in length
five to six pounds in weight
viability likely
fingernails completely cover fingertips
head hair replaces lanugo on head
4020 to 21 inches in length
seven to eight pounds in weight
viable, full term
body lanugo disappears
lungs mature


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