Anthem’s fourth-quarter earnings tumbled 64 percent as the health insurer absorbed some sizable expenses and booked fewer customers than it expected through the Affordable Care Act’s public insurance exchanges.

The Blue Cross Blue Shield insurer continued to expand its business from government programs like Medicaid and reaffirmed its forecast for the new year.

Overall, fourth-quarter earnings totaled $180.9 million, down from $506.7 million in the previous year’s quarter.

Adjusted results totaled $1.14 per share, while operating revenue, which excludes investment gains, rose more than 6 percent to around $20 billion.

Analysts expected, on average, earnings of $1.21 per share on $19.91 billion in revenue, according to a survey by the data firm FactSet.

Anthem operates plans in big markets like California, New York, and Ohio. It also sells coverage on public insurance exchanges in 14 states.

The insurer said Wednesday that in the fourth quarter it booked $51.5 million in costs tied to its pending acquisition of rival insurer Cigna Corp. and a charge of $42.3 million related to changes in tax calculations for California.

Operating revenue from the insurer’s government business, which also includes privately run Medicare plans, jumped 17 percent to more than $10.6 billion. Anthem made its name nationally as a provider of private Blue Cross Blue Shield coverage, but it pegs more of its future growth on government business.

Many states are expanding eligibility for Medicaid programs, which cover poor and disabled patients, under the ACA, and they also are asking insurers to run those programs.

‘‘We expect to be front-and-center supporting these states’ initiatives,’’ chairman Joseph Swedish told analysts during a Wednesday morning conference call.

The company also expects to expand its government business even more once it completes its $48-billion acquisition of Cigna and adds that company’s Medicare Advantage customers. That acquisition is undergoing regulatory review, and it has drawn concern from doctor groups and some members of Congress over how it may affect consumers.

Anthem said Wednesday it still expects the deal to close in the second half of this year.

The insurer covered 791,000 people through the ACA’s public exchanges at the end of last year. Unlike other insurers, Anthem said that business has been profitable, but enrollment came in about 30 percent lower than it expected.

Larger rival UnitedHealth Group Inc. and other insurers have said their exchange business has struggled in particular with customers who have been allowed to sign up outside open enrollment periods. Those customers tend to generate more claims than those who sign up during open enrollment.

Swedish told analyst Wednesday that his company is paying close attention to how the government handles these special enrollment periods as it judges how sustainable the exchange business will be in the future.

The Indianapolis-based insurer also said Wednesday that it still expects 2016 adjusted earnings per share to be greater than $10.80.

Analysts expect, on average, $10.90 per share.