For more details on methods see the following publications:
"Monthly Estimates of the Quantum of Fertility: Towards a Fertility Monitoring System in Austria" (T. Sobotka, M. Winkler-Dworak, M. R. Testa, W. Lutz, D. Philipov, H. Engelhardt, and R. Gisser). Vienna Yearbook of Population Research 2005: 109-141.
Link to the article
Appendices to the article

"Geburtenbarometer Vienna: Analysing Fertility Convergence between Vienna and Austria" (Kryštof Zeman, Tomáš Sobotka, Richard Gisser, Maria Winkler-Dworak, and Wolfgang Lutz). VID Working Paper 07/2011
Link to the article

Data on population and births, publications, and documentation of Statistics Austria are available at:
Link to the division website