Scientists examined results from clinics in Denmark, Sweden and Spain.
In Pictures: Edinburgh Pride parade marks Stonewall anniversary
In Pictures: Crowds greet the sun on the longest day of the year
In Pictures: Racegoers turn on the style for Royal Ascot fashion stakes
In Pictures: Flooding clear-up begins as further deluges predicted
In Pictures: Rally good fun for classic car enthusiasts
In Pictures: Rivers rise and residents rescued amid relentless rain
In Pictures: William and Kate visit Cumbria countryside