6. FULL TERM FETUS
A full-term fetus is defined as one born between 39 weeks, 0 days and 40 weeks, 6 days of gestation, which is considered the optimal time for birth to ensure full organ development, particularly the lungs and brain. While 37–42 weeks was historically considered full-term, current guidelines distinguish between early-term (37-38 weeks) and full-term (39+ weeks).
March of Dimes +2
5. 22-24 week fetus
At 22–24 weeks, the fetus is fully formed, measures roughly 11-12 inches (28-30 cm), and weighs over 1 lb (450g-600g+), appearing similar to a small, skinny newborn. They are developing rapid eye movements, hearing, and refined touch, while the lungs begin forming air sacs. Viability is possible by 24 weeks.
Mayo Clinic +5
Key Fetal Development (22-24 Weeks)
4. 20-22 WEEK FETUS
At 20-22 weeks, the fetus is about 11 inches long and weighs roughly 1 lb, having developed a, sleep-wake cycle,, refined senses of hearing and touch, and covered in protective vernix and lanugo. This stage marks the limit of viability (around 22 weeks), where the fetus can sometimes survive outside the womb with intensive care.
Mayo Clinic +4
3. 16-18 weeks foetus
Between 16 and 18 weeks, the fetus grows rapidly, reaching about 5.5 inches and 7 ounces, with recognizable facial features, working limbs, and developing hearing. The skin is translucent, showing blood vessels, and covered in fine hair (lanugo). At 18 weeks, they may start hearing sounds, and gender is often visible on ultrasound.
Mayo Clinic +3
2. 8-12 WEEK FETUS
Between 8 and 12 weeks, the embryo becomes a fetus, growing from the size of a raspberry to a lime (approx. 2.5 inches and 0.5 oz). All major organs and body systems form, webbed fingers/toes separate, and nails begin to develop. By week 12, the fetus has a distinct human profile and active movement.
Cleveland Clinic +5
1. 4 WEEK FETUS
At 4 weeks pregnant, the developing baby is formally called an embryo (not a fetus) and is about the size of a poppy seed, measuring roughly
. It has implanted in the uterus and is forming layers that will become organs, along with the amniotic sac and placenta.