First Trimester: (At 4 weeks gestation) The heart, brain, and arms & legs start to form. You baby is now an embryo. (8 weeks gestation) Your baby’s heart starts to beat regular and the umbilical cord is now visible. The major organs, external body structures, fingers & toes start to form. Your baby is now a fetus. (12 weeks gestation)
The nerves and muscles start to work together. The eyelids close to protect the eyes. The baby now can move on it’s own (but mom won’t be able to feel yet). (14 weeks gestation) Arms and legs can now flex. Baby can put hands to mouth. Hair follicles are appearing below the skin surface.
Second Trimester: (16 weeks gestation) The kidneys now can produce urine. The baby can now hear sound. The baby’s digestive system is working. The genitals are defined and you should be able to determine the baby’s gender at this time.
(20 weeks gestation) Lanugo and Vernix form (which helps protect the baby’s skin when forming). Fingernails and toenails are formed.
(24 weeks gestation) Footprints and fingerprints form. The baby sleeps and wakes regularly. The lungs are formed (but not ready to function outside of the womb). You may have already felt slight slight flutters but by now should start to notice movement. (28 weeks gestation) The eyes can now open and close. The baby starts to recognize familiar sounds (this can be determined by heart rate).
Third Trimester: (32 weeks gestation) Baby starts to gain weight quickly in the last few weeks. Baby’s brain is growing rapidly. (36 weeks gestation) The circulatory & musculoskeletal systems are complete. The protective coating (vernix) get thicker. (38-40 weeks gestation) After 37 weeks your baby’s organs are ready to function. At the end of the gestation the baby should start to present head-down for birth position.
