Portugal is characterised by a noteworthy decline in fertility, which is a phenomenon that requires some intervention given the costs, namely economic and political, associated with it. Notwithstanding the downward trend in fertility, a careful observation of the data on the number of births in Portugal indicates that there months where the number of births is clearly higher as well as others where the number of births seems to be smaller. This impression is confirmed by a time series analysis of the data, which shows that, in general, May and September are, indeed, months where more babies are born and that December and February are months where fewer babies are born. This fact is also evident from a prevision of the number of births throughout a whole year. Of particular importance is the detection of the factors explaining those two peaks in births as they may be manipulated by a demographic policy leading to an increase in fertility.