U.S. births recently hit a historic 30-year low and some say the numbers predict Social Security is in big trouble.

"It means that Social Security is in even bigger trouble than the actuaries estimated last time they did the numbers," says Romina Boccia, an expert on economics and government spending at The Heritage Foundation.

"Because they did, in fact, make an assumption about a fertility rate in the United States that would be more around 2 rather than 1.7, which is what this most recent CDC report shows."

Put it simpler terms, says the economic expert, it means Social Security's trust fund will run out of money sooner than expected, which is 2034.

Asked what will happen if lawmakers fail to address Social Security's lack of funding, Boccia says federal law stipulates that Social Security can pay out full benefits if it can do so via payroll taxes that are paid in or if it has assets in the trust fund.

"Once the trust fund is depleted in 2034, since the program is already running cash-flow deficits, payroll taxes are insufficient to pay full benefits," she explains. "At that point in time, it would only be able to pay about 75 percent of benefits due. So there could be an automatic benefit cut that would be almost 25 percent."

Heritage recommends lawmakers make Social Security reform a necessary and urgent priority because the longer they wait, the more costly the options on the table.

"If lawmakers don't do anything but just raise taxes in order to avoid indiscriminate benefit cuts, we're looking at the payroll tax going up by one-third from 12 percent to more than 16 percent," Boccia warns. "That would be devastating, especially for lower income and middle-class workers."