Going by the birth rate data, it would seem that there was little change in the birth rate between 1910 (30.1 per 1,000), 1915 (29.5 per 1,000) and 1920 (27.7 per 1,000).
It can be argued that the war didn't affect the population at all in that respect. However, another explanation can be that there are two conflicting forces working simultaneously. For instance, this was a period of increasing urbanization, which tends to lead to lower birth rates. This intersects with a baby boom after WWI, so the figures stay stable. Obviously, though, this is all just conjecture. I doubt it is possible to gather conclusive proof of peoples' motives.
Also, looking at the data for the 1920's, it seems that the "baby bust" between the wars can be correlated to the prohibition period. Birth rates start declining in 1920, have their lowest point in 1935 and are already rising by 1940, well before the American involvement in WWII started.