Baby Development

The First Nine Months

CONCEPTION: Father’s sperm penetrates mother’s egg cell. Genetic instructions from parents interact to begin a new and unique individual, no bigger than a grain of sugar.

First Trimester

  • 1st DAY: The first cell divides into two, the two into four, and so on.
  • 5-9 DAYS: The new life burrows into the wall of the womb. The sex can be determined.
  • 14 DAYS: Mother’s menstrual period is suppressed by a hormone produced by the baby.
  • 15 DAYS: Heart is forming; eyes develop.
  • 20 DAYS: Foundations of brain, spinal cord and nervous system are laid.
  • 24 DAYS: The baby’s heart begins to beat.
  • 28 DAYS: Muscles are developing along the future spine. Arms and legs are budding.
  • 30 DAYS: Th3 baby has grown 10,000 times to 6-7mm. (1/4 in.) long. Brain has human proportions. Blood flows in veins (but stays separate from mother’s blood).
  • 35 DAYS: Pituitary gland in brain is forming. Mouth, ears and nose are taking shape.
  • 40 DAYS: The baby’s heart’s output is 20% of an adult’s.
  • 42 DAYS: Skeleton is formed. Brain coordinates movement of muscles and organs. Reflex responses have begun. Penis is forming in boys. (Mother misses second period.)
  • 43 DAYS: Brain waves can be recorded.
  • 45 DAYS: Spontaneous movements have begun. Buds of milk teeth have appeared.
  • ​7 WEEKS: Lips are sensitive to touch. Ears may resemble family pattern.
  • 8 WEEKS: The baby is well-proportioned, 3 cm. (1 1/8 in.) sitting up,  and a gram (1/3 oz.) in weight. Every organ is present. Heart beats sturdily. Stomach produces digestive juices. Liver makes blood cells. Kidneys begin to function. Taste buds forming.
  • 9 WEEKS: The baby will bend fingers around an object placed in the palm. Thumb sucking occurs. Fingernails are forming.
  • 10 WEEKS: Body is sensitive to touch. The baby squints, swallows and frowns.
  • 11 WEEKS: The baby urinates, makes complex facial expressions, even smiles.
  • 12 WEEKS: The baby can kick, curl toes, make a fist, move thumbs, bend wrists, turn head, open mouth and press lips together. Breathing is practiced.
  • 13 WEEKS: Face is prettier, facial expressions resembling parents’. Graceful movements. Vocal cords forming (but without air baby cannot cry). Sex organs are apparent.

Second Trimester

  • 4 MONTHS: The baby can grasp with hands, swim and turn somersaults.
  • 4-5 MONTHS: As the mother, you will feel your baby moving.
  • 5 MONTHS: Sleeping habits appear. The baby responds to sounds in frequencies too high or low for adults to hear.
  • 6 MONTHS: Fine hair grows on eyebrows and head. Eyelash fringe appears. Weight is about 640g. (1 lb. 6 oz.) and height 23cm. (9 in.). Babies born at this age have survived.

Third Trimester

  • 7 MONTHS: Eye teeth are present. Eyelids open and close, eyes look around. Hands grip strongly. Your baby will recognize your voice.
  • 8 MONTHS: Weight increases by 1 kg. (over 2 lbs.) and baby’s quarters get cramped.
  • 9 MONTHS: The baby triggers labor and birth occurs, usually 255-275 days after conception.
For more information about baby development by week, refer to: