Marriages of twins to twins.
D000293:Adolescent; D000328:Adult; D001789:Blood Group Antigens; D004243:Divorce; D005260:Female; D006262:Health; D006801:Humans; D008297:Male; D008393:Marriage; D008603:Mental Health; D011247:Pregnancy; D014427:Twins
D001789:Blood Group Antigens