Cellular development of some embryonic organs and the chorion during the first trimester of human pregnancy.

The DNA, RNA and protein content of chorionic tissue, heart, liver, kidney, lung and brain was estimated in 27 fetuses obtained at termination of pregnancy between 50 and 105 days of menstrual age. For brain, heart and liver, growth appeared to be most rapid at the earliest period studied (50 to 60 days) whereas kidney and lung development was most rapid later in the first trimester. It is suggested that these periods of particularly rapid growth may be the times at which those tissues are most vulnerable to injury.