With maternity wards across the country forced to close last year as health workers were infected, birth registrations plummeted by almost 40 percent compared to 2013, the UN children's fund said, citing government estimates.
"Children who have not been registered at birth officially don't exist," Sheldon Yett, UNICEF's Representative in Liberia, said in a statement.
"Without citizenship, children in Liberia, who have already experienced terrible suffering because of Ebola, risk marginalisation because they may be unable to access basic health and social services, obtain identity documents, and will be in danger of being trafficked or illegally adopted."
Just 700 births were reported in the first five months of this year, UNICEF said, as local and international health authorities battled alongside aid workers to bring the outbreak under control.
A spokesman for UNICEF told AFP the Liberian government estimate of 70,000 unregistered babies was extrapolated from the projected number of births against actual registrations.
But he added that there was no data to show if the intense spread of the virus -- passed from human to human via bodily fluids -- led to a decline in actual births, which might explain in part the drop in registrations.
UNICEF is helping Liberia rebuild its shattered health services ahead of a government campaign planned for later in the year to reach all babies not registered during the epidemic.
Ebola has infected almost 28,000 people and killed nearly 11,300 across Liberia and its neighbours Guinea and Sierra Leone, according to official data widely thought to underestimate the real toll.
The highly-infectious tropical fever emerged in Guinea in December 2013, spreading across the border and killing 4,800 Liberians before the country was finally declared free of transmission on May 9.
It lost its "Ebola free" status, however, when a 17-year-old died in the coastal county of Margibi at the end of June after passing the virus on to five others, one of whom also died.
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