Historical birth records from 1896 to 1944 from the Basel maternity hospital, Switzerland, reveal significant obstetric selection pressures

Abstract

Maternal and neonatal morbidity and mortality have declined dramatically during the last century. Historical data are therefore important sources to study the evolutionary selection pressures related to childbirth and how they have fluctuated over time. We analyzed birth records detailing 17,473 births of the years 1896 to 1944 from the maternal hospital Basel, Switzerland. This enabled the evaluation of changes in anthropometric data across several generations during times of varying socioeconomic stress. Our results revealed very weak correlations ( r < 0.2) of maternal measurements such as stature and pelvic size with the size of the newborn (birth weight, head circumference). Maternal pelvic size was weakly correlated with stature ( r  = 0.33). While mean maternal stature showed a clear secular trend, increasing steadily by 5%, that is, from 153 cm for mothers born 1850 to 161 cm for mothers born 1923, birth weight fluctuated slightly during economically demanding periods, with an overall increase of only 3.8% from 3160 g in 1896 to 3280 g in 1944. In contrast, virtually no changes were found in pelvic size and newborn head circumference, implying the existence of strong stabilizing selection pressures on maternal pelvic dimensions and neonatal head circumference. We conclude that the resulting constant cephalopelvic proportion guarantees obstetric sufficiency as predicted by the obstetrical dilemma.