​During the third trimester, fetal development is characterized by rapid growth, organ maturation, and preparation for birth. The fetus gains significant weight as fat accumulates beneath the skin, helping with temperature regulation after delivery. Brain development accelerates, with extensive growth of neural connections that support sensory processing and coordination. The lungs continue maturing and increase surfactant production, which is essential for effective breathing after birth. Reflexes such as sucking, swallowing, and grasping become stronger and more coordinated. The immune system develops further as maternal antibodies are transferred to the fetus through the placenta. Bone development is complete, although the skull remains flexible to allow passage through the birth canal. Movements become powerful but less frequent as space in the uterus becomes limited. Most organ systems reach functional maturity during this period. By the end of the third trimester, the fetus is typically fully developed and capable of surviving independently outside the womb.

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Week 25

 

The startle reflex is well developed. Hair on the head becomes thicker and more pigmented. The lungs continue maturing structurally. Hand grasp strengthens, and fingers can curl. Balance organs in the inner ear develop further. Weight gain increases.
 

Size: 34.6 cm (rutabaga)

 

Week 26

 

Eyes open and close and begin responding to light. Surfactant production increases in the lungs. The nervous system improves coordination of breathing movements. The fetus responds to stimuli with more consistent patterns. Sleep cycles become more defined. The skin remains wrinkled but less translucent.
 

Size: 35.6 cm (scallion)

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Week 27

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The brain develops more complex folds and grooves. Lung-brain coordination improves. The fetus can regulate some aspects of breathing rhythm. Viability increases substantially at this stage. The immune system begins limited antibody reception from the mother. Fat accumulation accelerates.
 

Size: 36.6 cm (cauliflower)

 

Week 28

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Rapid brain growth continues, especially in regions controlling cognition and movement. Fat deposits increase beneath the skin. The fetus begins regulating body temperature more effectively. Eyes respond to light and can open fully. The nervous system becomes more responsive. The fetus demonstrates purposeful movements.
 

Size: 37.6 cm (eggplant)

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Week 29

 

Muscles and lungs continue maturing. Bones are fully formed but remain soft and flexible. Movements are strong and frequent. The fetus practices rhythmic breathing movements. The brain continues forming complex neural connections. Weight gain accelerates.
 

Size: 38.6 cm (butternut squash)

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Week 30

 

Bone marrow fully controls red blood cell production. Brain volume increases rapidly. Fat stores continue building. The fetus gains weight steadily. Taste perception improves. The fetus may hiccup frequently.
 

Size: 39.9 cm (large cabbage)

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Week 31

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The fetus continues rapid brain growth, particularly in areas responsible for sensory processing and coordination. Neural connections increase in number and complexity. The lungs near functional maturity, though breathing support may still be needed if born early. Reflexes such as sucking and grasping strengthen. The fetus responds consistently to sound and light. Fat accumulation increases, giving the body a rounder appearance.
 

Size: 41.1 cm (coconut)

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Week 32

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Fingernails and toenails are fully formed. The skin becomes thicker, smoother, and less translucent. Fat deposits increase beneath the skin, aiding temperature regulation. Breathing movements are regular and coordinated. The fetus practices swallowing amniotic fluid. Brain development remains rapid.
 

Size: 42.4 cm (jicama)

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Week 33

 

The skull remains soft and flexible to facilitate passage through the birth canal. The immune system continues developing. Breathing and swallowing are well coordinated. The fetus spends more time in sleep cycles, including REM sleep. Movements remain strong but space in the uterus is limited.
 

Size: 43.7 cm (pineapple)

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Week 34

 

The lungs are nearly fully mature. The central nervous system continues refining breathing control. Fat layers thicken further. The fetus shows more consistent temperature regulation. Most infants born at this stage have excellent medical outcomes.
 

Size: 45 cm (cantaloupe)

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Week 35

 

Rapid weight gain occurs as fat continues accumulating. The liver and kidneys are fully functional. The fetus occupies most of the uterine space. Movements feel strong but less frequent due to limited room. The brain continues developing rapidly.
 

Size: 46.2 cm (honeydew melon)

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Week 36

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The fetus typically assumes a head-down position in preparation for birth. The lungs are close to full maturity. The skin appears smooth and pink. Fat stores support temperature regulation after birth. Reflexes are strong and coordinated.
 

Size: 47.4 cm (romaine lettuce)

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Week 37

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The fetus is considered early term. Organ systems function independently. Brain development continues at a rapid pace. Coordination of sucking, swallowing, and breathing improves. The fetus responds actively to external stimuli.
 

Size: 48.6 cm (Swiss chard)

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Week 38: Full Term

 

The fetus is full term and is well prepared for life outside the womb. The lungs are fully mature. Most lanugo hair has been shed. Reflexes such as grasping are strong. The fetus continues gaining weight. Antibody transfer from the mother increases immune protection.
 

Size: 50 cm (watermelon)

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