A husband cannot have intercourse with his wife in the vagina when she is menstruating or in nifas. But he can be intimate by kissing, embracing, touching etc., parts that are above the navel and below the knee. Scholars differed on being intimate with regard to the area between the navel and the knee, apart from the front or back passage.

Sex during periods is prohibited not just because of the blood, rather it is for many reasons as stated in the detailed answer below.