"Financial decision makers in their own right, married women can benefit simply by having two people in the retirement savings equation," Weatherford said.

The report found that unmarried women are far less likely to ask for help from a financial advisor. Over two-thirds of unmarried women say they have never contacted a financial advisor for retirement planning advice, compared with 47% of married women.

"The need for retirement advice is arguably greater for unmarried women," Weatherford said. "Depending on circumstances, they may be looking to secure their retirement based on their income and assets alone, whereas married women likely are planning to rely on the savings and assets of their spouse as well."

Half of all women hold more than $500,000 in investable assets, she added, so, "this doesn't mean that unmarried women are without the resources to engage a financial professional to build a holistic retirement plan."

Advisors could well serve this investor segment by talking with unmarried women about retirement savings opportunities, as well retirement income needs like health and long-term care expenses, and the ins and outs of Social Security, Weatherford said.

"Unmarried women are just as eager as their married counterparts to have a secure financial future, and advisors that can help formulate both the accumulation and retirement income side will do well in serving this untapped market," she said.

IRI acknowledges that there are many similarities between the way men and women approach retirement planning. Approximately two-thirds of both men and women have contributed to a retirement plan in the past year, and more than half have calculated how much they'll need to retire. Both genders anticipate retiring at the same age (although majorities of both groups report not knowing when they'll retire), and both value guaranteed income, rate of return and principal protection most in a retirement product.

However, women are less confident than men and report not fully understanding some investments. Regardless of marital status, just 34% of women said they were confident they would have enough income to sustain them in retirement, compared with 41% of men. Nearly one-half of women said they are not knowledgeable about securities, compared with 40% of men.

Although 42% of men have contacted a financial advisor, over one-fifth are willing to forgo an advisor's help and do their own planning. Among women, 47% have contacted an advisor, but just 15% reported that they were able to do their own financial planning. Among those who have a financial advisor, more than one-third have been with the advisor for more than 10 years.