you're probably just getting unlucky and winning the 10% unknown creature roll on pregnancy also with womb seedbed 10 you can technically use a single abortion pill to test if it is abomination without having to wait to know based on baby health on menu since 1 abortion pill + a blue potion at seedbed 10 will instantly kill other pregnancies that are possible

Oh yes and abomination birth doesn't work like deepone birth you sell the monster babies to elise with the sell baby option these monsters are red