Wellesley Bank’s parent company posted a first-quarter net loss of $553,000, but blamed the results on a one-time, $1.8 million contribution to a charitable foundation formed in connection with its recently completed mutual-to-stock conversion and public offering.

The $553,000 net loss for the quarter ended March 31 compared with a $492,000 gain in the same period last year. Exclusive of the $1.8 million, conversion-related cost, pre-tax earnings for the three month period ending March 31 increased $50,000 compared with the same period last year, the company said in a statement.

The provision for loan losses was cut in half to $150,000 as of March 31, from $300,000 in 2011, as impaired loans declined.

Wellesley Bank opened its third branch last month in Wellesley, in the Lower Falls section of town.

Total assets rose $11 million in the three months ended March 31 to $314.2 million. Net loans because of growth in the bank’s adjustable-rate mortgage portfolio. Construction loans rose $3.8 million from increased lending efforts in that market, according to the company.

Deposits increased $4.4 million during the three months ended March 31 to $249.6 million.