Most research on trends in socio-economic fertility differences has
focused on cohort total fertility and on women. This study aimed to
analyse how cohort trends in parity-specific fertility differ across
educational segments for men and women and what role multi-partner
fertility plays in these trends. We used Finnish and Swedish register
data on cohorts born in 1940–73/78. The main analyses used parity
progression ratios, comparing ordinary ratios with similar ratios using
births to first reproductive partners only. Among the low and medium
educated, we observe strengthening parity polarization across cohorts,
with increases in both childlessness and births of order three or
higher, the latter largely reflecting increases in multi-partner
fertility. Highly educated men and women more often have exactly two
children. We demonstrate that cohort total fertility can mask
significant parity-specific trends across educational groups and that
changes in multi-partner fertility can play a part in cohort trends in
socio-economic fertility differentials.