The Obama administration launched the healthcare insurance website after only a minimum of crucial system-wide testing, despite contractors’ warnings.
Last minute design changes and barely two weeks of testing of the online system’s technology backbone have been blamed to contribute to the problems, limiting access to the site, after its launch earlier this month.
The issues were discussed during a US House of Representatives oversight committee hearing.
"Due to a compressed time frame, the system wasn't tested enough," said Julie Bataille, a spokeswoman for the Centers for Medicare and Medicaid Services (CMS), the US governmental agency implementing the online marketplace.
"It’s important to realize that we are putting in place a much more robust performance testing system now."
Describing the Healtcare.gov web portal as one of the most complex large-scale IT systems, the contractors speaking during the hearing have agreed several months of testing would have been needed to tune the performance of the system.
"We would certainly have liked to see as much time as possible for end-to-end testing," said Andrew Slavitt, executive vice president for the parent of CGI Federal and Quality Software Services (QSSI), a unit of health insurer UnitedHealth Group.
QSSI produced the federal data hub and a software tool for creating online consumer accounts, which was at the centre of early logjam problems. The last minute design change involved turning off anonymous browsing and requiring online visitors to create accounts before researching health plan information and determining their eligibility for federal subsidies to help pay premiums.
The 4-1/2-hour hearing before the House Energy and Commerce Committee marked the first full-length public airing over the problematic rollout, giving lawmakers the chance to piece together what went wrong at the beginning of a six-month enrolment period expected to draw at least 7 million enrolees for 2014.
The rollout went ahead after QSSI said it made CMS aware of its concerns throughout the system's development, but Slavitt was not aware of any response from the agency.
"The concerns that we had, which were mostly related to testing and the inability to get as much testing as we'd like - we expressed all of those concerns and risks to CMS," he said. "My understanding is they understood those and were working on them. But I don't know further."
The glitches, delays and errors that have characterized the website are a growing concern for Republicans and Democrats alike. The administration is racing to solve the problems in time for millions of uninsured Americans to enrol for coverage and begin receiving health benefits from 1 January, as stipulated by the 2010 Affordable Care Act, commonly called "Obamacare."
CMS said on Thursday that about 700,000 applications had been submitted so far for U.S. healthcare coverage through the exchanges.
The Department of Health and Human Services and the White House have largely declined to disclose information about the problems plaguing the system, which cost nearly $400 million to build.