Week: 1 size: 0.0035 in (0.008 cm). A mature egg is released from the ovary. The egg moves into the Fallopian tube. A sperm fertilizes the egg to form a zygote.
Week: 2 size: 0.0039 in (0.0099 cm). The zygote travels down the Fallopian tube. The zygote is implanted into the uterine wall. The cells of the early embryo begin to divide.
Week: 3 size: 0.0039 in (0.0099 cm). The implantation of the embryo is complete. The early embryo now consists of 16 cells. It continues to divided to from the blastocyst.
Week: 4 size: 0.01 in (0.025 cm) weight: 0.0001 oz (3.95 mg). The blastocyst forms the embryonic dice. The embryo is now made of three layers. Each layer will form different parts of the body.
Week: 5 size: 0.13 in (0.33 cm) weight: 0.01 oz (0.28 g) Tiny collection of tubes will start to form. One tube forms the brain & the spinal cord. Another tube develops into the baby's heart.
Week: 6 size: 0.25 in (0.63 cm) weight: 0.02 oz (0.56 g). The buds develop and will soon become arms. The eyes and ears are beginning to develop. The tiny developing heart beings to beat.
Week: 7 size: 0.51 in (1.29 cm) weight: 0.03 oz (0.85 g). The baby's brain continues to develop. Face and nostrils start to take shape. lungs and digestive system branch out.
Week: 8 size: 0.63 in (1.6 cm) weight: 0.04 oz (1.13 g). Fingers and arms start to take shape. The baby's ears and eyes become obvious. Kidneys, liver and lungs begin to develop.
Week: 9 size: 0.09 in (2.2 cm) weight: 0.07 oz (1.98 g). Toes are visible and eyelids are now forming. The baby's head is huge compared to the baby. The legs are now becoming more defined.
Week: 10 size: 1.2 in (3 cm) weight: 0.14 oz (3.96 g). The baby's head is becoming more round. The baby has now well-defined eyes. The webbing between fingers and toes is gone.
Week: 11 size: 1.6 in (4 cm) weight: 0.25 oz (7 g). Fingernails and irises start to grow. Red blood cells begin to form. External genitalia start to develop.
Week: 12 size: 2.1 in (5.3 cm) weight: 0.5 oz (14 g). kidneys are ready to produce urine. The intestines are now developing. The risk of miscarriage goes down.
Week: 13 size: 2.9 in (7.3 cm) weight: 0.8 oz (22.6 g). Baby releases urine into the amniotic sac. Bones begin to harden to form skeleton. The skin is still thin and transparent.
Week: 14 size: 3.5 in (8.8 cm) weight: 1.5 oz (42 g). The baby's body is covered with soft hairs. The neck has become more defined. Fingerprints are now developing.
Week: 15 size: 4 in (10.1 cm) weight: 2.5 oz (71 g). Networks of blood vessels begin to from. Facial expressions are now noticeable. Scalp hair pattern is beginning to from.
Week: 16 size: 4.5 in (11.43 cm) weight: 4 oz (113 g). The developing eyes can move slowly. Limb movements are now coordinated. The baby is now the size of a small apple.
Week: 17 size: 5.1 in (13 cm) weight: 5.9 oz (167 g). The lungs are breathing in amniotic fluid. The heart pumps 100 pints of blood a day. Toenails are now beginning to grow.
Week: 18 size: 5.5 in (14 cm) weight: 7 oz (200 g). The baby can hear external sounds. The digestive system is now working. The mother can feel the baby's movement.
Week: 19 size: 6 in (15.24 cm) weight: 8.5 oz (240 g). The growth of the baby is slowing down. A protective layer forms around the baby. This layer protects the baby's delicate skin.
Week: 20 size: 6.3 in (16 cm) weight: 11 oz (312 g). The baby can now sleep and wake up. The baby can feel mother's movements. The baby can now respond to sounds.
Week: 21 size: 10.5 in (26.6 cm) weight: 12.7 oz (360 g). The baby begins sucking his or her thumb. Tiny tooth buds pop up in the baby's gums. The intestines begin producing solid waste.
Week: 22 size: 10.9 in (27.6 cm) weight: 15.2 oz (431 g). Rapid eye movements may now occur. Eyebrows and hair are now more visible. Sex organs are developing more rapidly.
Week: 23 size: 11.4 in (28.9 cm) weight: 1.1 lb (499 g). Baby's Hiccups now trigger more movement. The brain is now making neural connections. The baby's face is becoming more defined.
Week: 24 size: 11.8 in (30 cm) weight: 1.3 lb (589 g). The skin is now wrinkled and translucent. Blood vessels are visible through the skin. The baby's fingernails are now fully formed.
Week: 25 size: 13.6 in (34.5 cm) weight: 1.5 lb (680 g). The baby spends most of the time sleeping. The baby's heartbeat becomes clearer. The baby can distinguish up from down.
Week: 26 size: 14 in (35.5 cm) weight: 1.7 lb (771 g). Eyelids have formed and can now open. The eyes are still bluish in color. The immune system begins to develop.
Week: 27 size: 14.4 in (36.6 cm) weight: 1.9 lb (861 g). The nervous system continues to mature. Signs of brain activity can now be detected. The baby's lungs begin inhaling and exhaling.
Week: 28 size: 14.8 in (37.5 cm) weight: 2.2 lb (998 g). The eyelashes are now fully formed. Breathing is controlled by nervous system. The baby will start to blink and cough.
Week: 29 size: 15.2 in (38.6 cm) weight: 2.5 lb (1.1 kg). The baby begins moving into birth position. The baby can now kick, stretch and jab. The baby can sense sound, light and touch.
Week: 30 size: 15.7 in (39.8 cm) weight: 3 lb (1.3 kg). The developing eyes are now wide open. There is a good amount of hair on the head. More red blood cells form in bone marrow.
Week: 31 size: 16.2 in (41.1 cm) weight: 3.3 lb ( 1.5 kg). All baby's five senses are now working. The baby begins gaining weight rapidly. Brain and nerve development continue.
Week: 32 size: 16.2 in (42.4 cm) weight: 3.8 lb (1.7 kg). Hair that covers the skin is falling off. The baby's toenails are now visible. The head is switching to birth position.
Week: 33 size: 17 in (43.1 cm) weight: 4.2 lb ( 1.9 kg). Breathing and swallowing are coordinated. The bones are now becoming stronger. The baby's skull is still soft and flexible.
Week: 34 size: 17.2 in (43.6 cm) weight: 4.6 lb(2 kg). The baby has switched to the birth position. Major organs can work on their own. Digestive and respiratory systems are functional.
Week: 35 size: 18.2 in (46.2 cm) weight: 5.3 lb (2.4 kg). The skin is becoming pink and smooth. The baby's hearing is now fully developed. The baby is setting into delivery position.
Week: 36 size: 18.7 in (47.5 cm) weight: 5.8 lb (2.6 kg). The liver and the kidneys are fully functional. Circulation and the immune system are working. The womb is becoming too tight for the baby.
Week: 37 size: 19 in (48.2 cm) weight: 6.1 lb (2.7 kg). The baby is now practicing gripping. The baby is discharging sticky waste. The baby is now just about full-sized.
Week: 38 size: 19.2 in (48.7 cm) weight: 6.3 lb (2.8 kg). The head's hair is now longer and denser. The baby sheds the white goo on the skin. The brain is now controlling other organs.
Week: 39 size: 19.5 in (49.5 cm) weight: 7 lb (3.1 kg). The baby's nails extend past the fingertips. The chest is becoming more prominent. The brain continues to rapidly develop.
Week: 40 size: 20.2 in (51.3 cm) weight: 7.4 lb (3.3 kg). All organs are developed & working. The baby has now reached full term. The fully developed baby is born.