Table 1.

Comparisons between neonatal niche injection and blastocyst complementation, as well as fetal injection.

	Neonatal niche injection (P1.5)	Blastocyst complementation (E2.5)9	Fetal injection (Exo utero, E13.5)11
Second surgery	Not required	Embryo transfer to pseudopregnant mice	Cesarean section and transfer to foster mothers
Host survival rate	85% (33 of 39)a	43% (34 of 79)b p < 0.0001c	74% (14 of 19)d p = 0.47c
Percentage of donor nephron engraftment in kidneys relative to surviving hosts	100% (33 of 33)	71% (24 of 34)e p < 0.0001c	14% (2 of 14) p < 0.0001c
Percentage of donor nephron engraftment in kidneys relative to all injected hosts	85% (33 of 39)	30% (24 of 79) p < 0.0001c	11% (2 of 19) p < 0.0001c

^aHosts that survived 2 weeks after the surgery performed by the skilled experimenter.

^bPercentage of pups that reached adulthood from embryos derived from intercrosses of Sall1^+/− mice injected with embryonic stem cells.

^cComparisons against neonatal niche injection using the Chi-square test.

^dPercentage of fetuses that survived until cesarean section performed by the skilled experimenter. Note the subsequent risk of being killed by foster mothers.

^ePercentage of adults derived from embryos injected with embryonic stem cells, exhibiting confirmed chimera formation.