Baby Chris is 23 Weeks Old

[This is part 24 of a multi-part series chronicling a pregnancy through the lens of "Baby Chris." Click here for other parts.]

23 weeks after fertilization (25 weeks LMP), Baby Chris is 13 and a half inches long and weighs a pound and a half—roughly the size of a rutabega.

Illustration via BabyCenter.com

At this stage, respiratory system development is crucial. Baby Chris practices breathing by drawing amniotic fluid into the lungs. According to the Endowment for Human Development:

The fetal respiratory rate can rise as high as 44 inhale/exhale cycles per minute at 22 to 26 weeks. This rate changes according to maternal carbon dioxide (CO2) levels, strongly suggesting that the respiratory center in the brainstem of the fetus already detects and responds to changes in CO2 levels in the blood. This respiratory response to CO2 levels is similar to that seen in newborns and adults.

For more fetal development facts, download the free "See Baby" app on your smartphone.