Fetal health stagnation: Have health conditions in utero improved in the United States and Western and Northern Europe over the past 150 years?

•Birth weight means and distributions have been stable since the 19th c.•Perinatal mortality decline in 20th c. driven by intrapartum interventions.•This suggests either fetal health has been stagnant since the 19th c.•Or proxies for fetal health, birth weight and perinatal mortality, are problematic.•More research focussing on changes in fetal health over time is needed.

Many empirical studies have shown that health conditions in utero can have long lasting consequences for health across the life course. However, despite this evidence, there is no clear consensus about how fetal health has changed in the very long run. This paper analyses historical birth weights and perinatal mortality rates to construct a coherent picture of how health conditions in utero have changed over the past 150 years. In short, the evidence suggests that fetal health has been relatively stagnant. Limited evidence on birth weights shows that they had already reached their current levels in North America and Northern and Western Europe by the late nineteenth century, and they have changed very little in between. Perinatal mortality rates have fallen dramatically since the late 1930s, but this decline was mainly caused by improvements in intrapartum treatments after the introduction of Sulfa drugs and antibiotics. Thus, the health benefits associated with the perinatal mortality decline were concentrated among those at risk and did not influence the population at large. Finding stagnant fetal health during a period when many other indicators of health improved dramatically is provocative and suggests two conclusions: either fetal health did not improve or the indicators used to measure fetal health, indicators still widely used today, may not accurately capture all aspects of health in utero. If fetal health has been stagnant, then better conditions in utero cannot explain cohort improvements in life expectancy over the twentieth century. If the indicators of fetal health are problematic, then researchers must move beyond birth weight and perinatal mortality to understand how developmental plasticity based on the prenatal environment influences later life health.