Is the divorced wife obligated to observe an iddah if she sought divorce due to the husband's inability to procreate, owing to the absence of sperm, and what is the expiation for her non-observance of the iddah due to her ignorance of the ruling?

A divorced woman must observe the 'iddah (waiting period), even if the husband's infertility or the purity of the womb is established. The 'iddah has purposes other than ensuring the purity of the womb. If a divorced woman fails to observe the 'iddah out of ignorance, she incurs no sin. However, if she marries during the 'iddah period, her marriage contract is void and must be renewed. Neither spouse is obligated to inform the other of their infertility before marriage.