|Figure via the Endowment for Human Development|
Baby Chris's heart, which has been beating since 18 days after conception, now has a more matured four-chamber structure. It now beats between 167 and 175 times per minute; it will decline to about 140 beats per minute at birth.
The reproductive system is emerging with the formation of ovaries or testes. (We chose the gender-neutral name "Baby Chris" to represent unborn children of all sexes.)
Fingers and toes are starting to separate but are still somewhat webbed. Until now, Baby Chris's skeletal system has consisted solely of cartilage and membranes, but that is beginning to change as bones ossify in the collar bone and jaw. Also appearing by seven weeks: taste buds, elbows, and hiccups!
Baby Chris is approximately 14 mm long and continues to grow at a rapid pace. For more information on Baby Chris's development in the womb, download the free See Baby app on your smartphone.