An improved procedure for the efficient injection of radioactive steroids into mouse embryos

Retention of 3H-moxestrol in mouse fetuses after transmaternal, intrafetal, and intraplacental injection were compared. Direct injection into the allantoic placenta resulted in greater retention of radioactivity by the fetus than the other modes of administration between 12 and 16 days of gestation. By this same criterion, intrafetal injection was best for older fetuses. Maternal injection was the least efficient way to transfer 3H-moxestrol to the fetus.