Whether health insurers Aetna and Humana can merge will likely soon be decided, and the outcome might just have an impact on the price you pay at the doctor’s office.

A new study from researchers at Harvard shows what could happen to the amount policyholders have to pay for a doctor’s visit.

The findings, published in Health Affairs, show that the lower prices consumers pay shopping wholesale — for example, at Costco — also apply to health care. Insurance companies with more buying power – through having more policyholders – pay lower prices for health care services. For instance, insurers with more than 15 percent of a market population paid the least amount for an office visit: $70. That increased to $88 for an insurer with less than 5 percent of marketshare.

“Our results indicate that insurers with substantial bargaining power pay rates that are 21 percent lower, on average, than the rates paid to the same providers by insurers with little bargaining power,” the study authors write.

Medical providers set payment rates but insurance companies pay a portion of that rate. It’s common practice that if a health provider is ‘in-network,’ a patient will only pay a co-pay. But when patients go ‘out-of-network,’ they usually pay the total cost that the insurance company doesn’t cover.

The study also says that there might need to be more policies to limit the influence of having so much market share as a result of consolidation.

Study authors looked at over 15 million health care claims from a national database of 60 insurance companies in every state. Large insurers were able to negotiate lower prices with large provider practices.

A decision will likely come before February 15, the deadline Aetna and Humana have set for finalizing the $37 million deal.