Baby Chris is Four Weeks Old

[This is part 5 of a multi-part series chronicling a pregnancy through the lens of “Baby Chris.” Click here for other parts.]

Photo via Visible Embryo. This is a dorsal (rear) view.

Four weeks after his or her conception, Baby Chris is growing rapidly. Last week’s circulatory system development has enabled a burst of activity. The heart is now beating between 105 and 121 times per minute. “Pacemaker cells” have developed to control its rhythm.

Baby Chris’s skin is only one cell thick and translucent (right), allowing researchers a mostly unobstructed view of his or her many organs. The kidneys, gonads, and endocrine system are all developing. The left and right hemispheres of the brain are starting to emerge, and Baby Chris’s head is about a third of his or her entire body size. He or she also has “lung buds” and mainstem bronchi, the beginnings of the respiratory system. Placental connections are still forming, so Baby Chris continues to rely on the yolk sac for nourishment.

Remember to download the See Baby app on our smartphone for more information about Baby Chris’s 9-month journey from conception to birth!