What is the ruling on a husband taking back his wife after divorcing her a second time, while she is eight months pregnant?

If this divorce is the second, then you may take back your wife before the expiration of her iddah (waiting period). The iddah of a pregnant woman ends upon her delivery. The رجعة (revocation of divorce) is effected by your saying: "I take back my wife," or by sexual intercourse.

If the iddah ends before the رجعة, then you cannot take her back except with a new marriage contract that fulfills the conditions and pillars of marriage, and the woman is entitled to a new mahr (bridal gift).