Vronsky has very clear codes of conduct that he follows throughout his life. His relationship with Anna is clear: he will treat her with respect; no one in society whispers a word of slander; and the husband is superfluous. However, Anna’s pregnancy throws off his rules, and he doesn’t know how to proceed.
Vronsky has set clear rules for himself governing how he should live, much as Karenin has done; Anna’s pregnancy impacts him insofar as it alters how his relationship with Anna fits into the scheme of his life. Vronsky is governed by his own ambitions, not by passion.
Vronsky also realizes that his affair with Anna has distracted him from his career ambitions. His childhood friend Serpukhovskoy has just received promotions and awards, although he and Vronsky had been of the same rank. However, Vronsky decides that he cannot envy Serpukhovskoy because he has Anna’s love.
Vronsky has spent his life grooming himself for his own ambitions and desires. Although Anna appears as though she may derail him, he weaves her into his own selfish motivations: Vronsky thinks about Anna’s impact on him as a marker of private status.