Insurers cannot take gender into account as a risk factor in the costs and payouts from annuities and retirement savings as well as accident cover, the European Union's top court ruled on Tuesday.

Taking the gender of the insured individual into account as a risk factor in insurance contracts constitutes discrimination, the court said in a statement.

The ruling by the European Court of Justice could increase the costs of women's accident insurance as well as boost their retirement income, though it could also make men worse off, with major implications for the insurance sector.

The rule of unisex premiums and benefits will apply with effect from December 21, 2012, the court added.

The transitional period would allow EU member states to decide what action to take on domestic laws and give companies a chance to adjust and find ways to mitigate the knock-on effect.

(Reporting by Michele Sinner, editing by Rex Merrifield)