It will always be 1:1 for large number of couples…

Take any number as couples N e.g. 1028.
There will be 512 boys & 512 girls at first delivery….. (1:1)
Couples with Boy stops reproducing & 512 couples with Girls take another chance.
There will be 256 boys & 256 girls in second chance…..(1:1)
256 Couples with Boys stop reproducing & 256 Couples with 2 Girls Now will take another chance….
There will be 128 boys & 128 girls in third chance………(1:1)
128 Couples with Boys stop reproducing & 128 Couples with 3 Girls Now will take another chance….
There will be 64 boys & 64 girls in fourth chance………(1:1)
and ratio will continue till everyone has a boy each………………….then at end there will be N boys &  N-1 girls…
So ratio will be N:N-1 which is 1:1 in case of large sample size of N.