1 Week: The baby, called a blastocyst at this stage, is burrowing into the uterine lining. The baby is growing, with cells rapidly multiplying to begin organizing into the layers of cells which eventually develop into the various body systems.
4 Weeks: This can be the time a woman realizes she is pregnant. This is about the time the first period is missed. (Age of the baby is counted from the last menstrual period not conception.) The baby is becoming more complex as the cells continue to organize into different layers. Baby’s heart started beating at about 18 days after conception (2.5 weeks).
8 weeks: Body shape is very recognizable, fingers and toes are developing. Baby’s brain network is forming, and baby is constantly in motion – though movement usually isn’t noticeable until 12 – 15 weeks of pregnancy.
10 weeks: The baby is now about 1 inch long, has the basic systems including kidneys, brain, intestine and liver, and is swallowing and kicking around in the womb. Fingers and toes are separated and beginning to grow nails, and body hair is beginning to grow.
11 weeks: Tooth buds are appearing, bones are beginning to harden. Baby is exercising, clenching tiny fists and stretching, like water aerobics.
12 weeks: Baby is about 2 inches long now. Nervous system is making connections and synapses at a furious pace. Baby demonstrates reflexive movement, and will react to stimulus; prodding mother’s abdomen makes baby squirm.
13 Weeks: In addition to already having her own unique DNA, the baby now has unique fingerprints.
14 Weeks: Baby is making faces now, squinting and grimacing, and stretching and kicking. You probably can’t feel the kicking yet but it will come soon! Baby is about 3.5 inches long.
18 Weeks: Baby is about 5.5 inches long and his kicks and punches can be felt. Genitals are developed, though may not be visible yet in an ultrasound – some babies are shy about that!
22 Weeks: Baby is now about 11 inches long and weighs almost a pound. Features are more developed, tooth buds are forming, and eyes are developed but do not yet have the pigment for the iris.
26 Weeks: Baby’s ears are more developed and can now distinguish other voices than just mom’s. Baby is practicing breathing, taking in amniotic fluid. Baby is about 14 inches long now and starting to gain weight.
31 Weeks: Baby is about 3 pounds now, and will continue to gain weight until birth. There should be lots of activity now as baby stretches, turns, and kicks.
36 Weeks: Baby is early-term; there are about 4 weeks left until delivery. Baby weighs about 6 pounds now, and is getting ready for life outside. She’s swallowing amniotic fluid which will become meconium (first bowel movement) after birth.
40 Weeks: Baby is now full-term and delivery is imminent. He’s about 7.5 pounds now, and should be lowering into position for birth.