NEW YORK (Reuters) - MBIA Inc, (MBI.N: Quote, Profile, Research) a bond insurer struggling to maintain the top credit ratings necessary for its business, posted a fourth-quarter loss on Thursday after a $3.5 billion write-down.

The world’s largest bond insurer posted a loss of $2.3 billion, or $18.61 a share, compared with profit of $181 million, or $1.32 a share in the same quarter the previous year.

The company said it was writing down $3.5 billion on its credit derivatives portfolio, including a credit impairment of $200 million it expects to actually incur.

http://www.reuters.com/article/ousiv/idUSL3147636920080131