Main divisions of baby’s body – head, chest, abdomen, pelvis – are established and can be easily identified. Baby measures approximately ¼ of an inch long from head to rump – already 10,000 times bigger than the newly fertilized oocyte.

Day 26

  • Lungs begin to form.
  • Outlines of baby’s brain and eye vesicles can be seen.
  • The basic structure for baby’s entire central nervous system (brain and spinal cord / notochord) is formed.
  • Mouth, pharynx, abdominal cavity and basis of skeleton are developing.
  • Baby’s heart now beats 80 times per minute.

Day 28

  • Tiny arms begin to bud (legs begin to bud two days later); muscles are forming.
  • Baby’s heart is pumping its own blood. All 4 chambers of the heart are present and more than 1 million heartbeats have already occurred. Baby’s blood flows in new veins – the placenta forms a unique barrier that keeps mom’s blood separate while allowing food and oxygen to pass through to baby through vessels that intertwine without joining, highlighting the new symbiotic relationship – mutual, nourishing, deeply connected.
28 day old human embryo. Image Credit: Carnegie Stages

28 day old human embryo.
Image Credit: The Multi-Dimensional Human Embryo