The U.S. Census Bureau article U.S. Births Declined During the Pandemic by Anne Morse (9/21/2021) has the data.
However, comparing one month during the pandemic to the same month before the pandemic shows a substantial drop that can’t be explained by seasonality.
There were 285,138 births in December 2020 — 23,664 (7.66%) fewer than in December 2019. On average, there were 763 fewer births each day in December 2020 than in December 2019.
Not all of the decrease in births should necessarily be attributed to the pandemic. The number of U.S. births has been declining every year since 2008 (except 2014).
Between 2000 and 2019, the number of daily births declined an average 0.39% a year. The pace of decline accelerated between 2010 and 2019, when the number of daily births dropped on average 0.96% a year.
But the decline was much steeper in in 2020: The average number of daily births was 4.06% lower than in 2019.
There is a table of data in the article and sources are cited for the data.