What is the ruling on postponing the fulfillment of a vow to perform Umrah in the first Ramadan after marriage, and could failing to fulfill it be a reason for not conceiving?

A vow of obedience to God must be fulfilled, and it is not permissible to delay it without a valid excuse. Delaying it without an excuse incurs a sin that necessitates repentance and an expiation for breaking an oath (kaffarat yamin). The absence of offspring may be a result of sins and transgressions, so repentance, supplication (du'a), and seeking forgiveness (istighfar) are among the causes of provision. There is no harm in consulting specialized doctors, and the delay in having offspring does not mean their absence.