Fertility curves sometimes resemble sea waves. During periods that the fertility age patterns change, according to whatever reason, 'this sea' may become very turbulent. Also other sea-like phenomena, for example tsunamis, are discernible in fertility behaviour. This article gives a short overview of the relationships between age of the mother and the birth of her children by birth order, and the similarities with sea wave behaviour. We look at fertility behaviour from two perspectives: children born per calendar year versus mother's year of birth. Evidence comes from three European countries in the past decades. Politicians should keep distant from trying to change fertility levels as that easily can lead to regrettable waves in age group sizes.
Keywords: fertility curves; fertility patterns; TFR; total fertility rate; afe pyramid; mortality;
migration; policy measures