Is it permissible to be released from a vow to slaughter a calf for each newborn if there has been no pregnancy or birth for eight years, especially with the intention of undergoing an IVF procedure?

Undertaking a vow is disliked (makrooh). Whoever vows obedience to Allah must fulfill it, for the Prophet, peace and blessings be upon him, said: "Whoever vows to obey Allah, let him obey Him; and whoever vows to disobey Him, let him not disobey Him." Your vow, which you committed to, is a conditional vow. It becomes obligatory to fulfill it if the condition is met, and it is not permissible to be absolved from it. If no child is born, then nothing is binding upon you. The in-vitro fertilization (IVF) procedure is permissible with sharia-compliant regulations.