Only 700,000 newly-qualified Chinese couples have applied for having a second child this year.
The figure is far below earlier estimates that an easing in the country's birth policy would add one million to two million extra births per year in the first few years, health officials said.
Zhao Yanpei, a senior official at the National Health and Family Planning Commission, told reporters at a briefing this week that the number has been lower than expected but said it is too early to conclude how the new policy would affect China's birth rate.
Last year, China eased its one-child policy to allow couples where one partner has no siblings to have two children.
Couples where both partners have no siblings have been allowed to have two children for some time.