US commercial premiums grew 4% in the first quarter, as gains slowed to their lowest level since 2011, according to Towers Watson.

It compares with increases of 6% and 7% in the second half of 2012 and the first half of last year, with the moderating trend continuing for four consecutive quarters.

Employment practices liability posted the largest first-quarter increase, followed by excess/umbrella liability and commercial auto.

Rises for most lines were in the low to mid-single-digit range, with no standard commercial line reporting a decrease.

Specialty lines increased at a lower rate than standard lines, while account size made little difference to the level of gains.

Historical claim cost information points to a 2% improvement in loss ratios in accident-year 2014 compared with the previous year, as price increases offset claim cost inflation.

The loss-ratio movement builds on an estimated improvement of nearly 5% between 2012 and last year, according to the report.