Answered by Shaykh Faraz Rabbani
It has been suggested that we no longer need to sight the moon to determine the onset of Islamic months, as reliable astronomical calculations enable us to answer the question. If this is permissible, does it mean, by analogy, that women need no longer observe Iddah after divorce or bereavement, since pregnancy can reliably be excluded or confirmed by testing urine or blood, and by ultrasound scans. Moreover, DNA fingerprinting means paternity can be determined after birth in any event. I ask this question as I have some reservations about the use of technology that may lead us to forgo some aspects of the Sunnah.
Walaikum assalam,
1. While most contemporary scholars accept benefiting from calculations for exclusionary purposes, they affirm that actual eye-sighting is a condition for establishing the Islamic months and mention many benefits to it.
2. The reason behind idda is not only to establish that the woman is not pregnant: even a woman who did not have intercourse with her huband for years must go through this. The gravity of idda gives a powerful reminder to the individuals involved, and the society around them, about the seriousness of the marriage bond, the future benefits of which are obvious upon reflection.
And Allah alone gives success.
Wassalam,