i think more like “expected” one not to survive.
a natural reaction would be happiness both survived and beat the implantation stats.
One would think.
Implantation rate is perhaps 25%. So if they had 4 embryos introduced into the womb, then the expected number of implanted embryos would be 1, but the statistics would be
a 1x(1/4)^4 x (3/4)^0 =0.004 chance of 4 embryos implanting or
a 4 x(1/4)^3 x (3/4)^1 = 0.0469 chance of 3 embryos implanting or
a 6 x(1/4)^2 x (3/4)^2 = 0.422 chance of 2 embryos implanting or
a 4 x(1/4)^1 x (3/4)^3 = 0.422 chance of 1 implanting or
a 1 x(1/4)^0 x (3/4)^4 = 0.100 chance of zero embryos implanting
Rounded to three significant digits. This suggests they had an equal chance of one or two children, (both about 42%) with a 5% chance for 3 and less than 1% chance of 4.