Just like in the last Depression.
Births were declining well before the last depression... that, like this time, was likely a product of immigration reduction as well as a bad economy. Births peaked at just over 3 million in 1921 before falling slightly through 1925... but then began a huge slide after 1925 (coincidence, i think not) to 2.55 million by 1929. Births actually rallied slightly in 1930 and then fell to 2.3 million by 1933. Then began a slow rise from 1934-1938 before births rose significantly from 1939-1943 (to 3.1 million in 1943, before falling back to 2.9 million in 1945... then booming to record levels in 1946).
The birth patterns in this recession have been more akin to those of the early 70s. The age structure of the population indicates that births should be rising, but instead they are falling. While 4.3 to 4.0 million births is significant, there is evidence that births have already turned around for 2011. It is nothing like the fall from 3.1 million to 2.3 million between 1921 and 1933 or the fall from 4.2 million from 1960 to 3.1 million in 1973.
In fact, I'd suspect that births will remain quite stable and grow with the population with few of the dips and rises since the major booms and busts have now kind of "bred" themselves out.