(Bloomberg News) Variable-annuity sales in the U.S. increased for the fifth straight quarter, led by gains at Prudential Financial Inc. and MetLife Inc., as rising stock markets and changing terms spurred demand.

Sales climbed to $38.9 billion, or 24 percent, in the first quarter from $32.2 billion a year earlier, trade group Limra said today on its website. Prudential, the top provider of the retirement products, sold $6.81 billion, an increase 40 percent from a year earlier. New York-based MetLife ranked second as sales rose 41 percent to $5.68 billion.

Sales of equity-linked variable annuities increased as stock markets rebounded from March 2009 lows, cutting the risk insurers will shoulder losses on customers' guaranteed returns. The Standard & Poor's 500 Index climbed 5.4 percent in the first quarter after rising 13 percent last year. Savers may have boosted investments to lock in terms ahead of scheduled changes in benefits and fees.

"It's reasonable to assume that a portion of our first- quarter sales represented accelerated purchases due to the anticipated product changeover," Mark Grier, vice chairman of the Newark, New Jersey-based insurer, said on May 5 during a call with analysts to discuss first-quarter results.

MetLife has also changed terms, reducing guaranteed payout rates, Robert Sollmann, executive vice president of retirement products, said at a conference in February.

Insurers lost money on the products in 2008 and early 2009 because the funds are generally invested in stocks. The S&P 500 declined 38 percent in 2008.