By Gregori Galofré-Vilà (Universitat Pompeu Fabra and Barcelona Graduate School of Economics) and Bernard Harris (University of Strathclyde)
It is now widely accepted that early-life conditions have a significant effect on lifelong health (see e.g. Wells 2016). Many researchers have sought to examine intrauterine health by studying birth weights, but the evidence of historical changes is mixed. Although some researchers have argued that birth weights have increased over time (e.g. O’Brien et al. 2020), others have found little evidence of any significant change over the course of the last century (Roberts and Wood 2014). These findings have led Schneider (2017: 25) to conclude either that, ‘fetal health has remained stagnant’ or that ‘the indicators used to measure fetal health … are not as helpful as research might hope’.
The absence of unequivocal evidence of changes in birth weight has encouraged researchers to pay more attention to other intrauterine health indicators, including the size and shape of the placenta and the ratio of placental weight to birth weight (e.g. Burton et al. 2010). The placenta transfers oxygen and nutrients from the mother to foetus and provides the means of removing waste products. Although the evidence regarding changes in placental weight is also mixed, it has been described as a ‘mirror’ reflecting the foetus’ intrauterine status (Kaur 2016: 185).
Historical studies of changes in placental weights are still very rare. However, we have collected data on almost 4000 placentas which were weighed and measured at Barcelona’s Provincial House (La Casa Provincial de Maternitat i Expósits) between 1905 and 1920. Our new paper (Galofré-Vilà and Harris, in press) examines the impact of short-term fluctuations in economic conditions on placental weights immediately before and during the First World War, together with the relationship between placental weights and other maternal and neonatal health indicators and long-term changes in placental weight over the course of the century.
Our first aim was to compare changes in birth weight with changes in placental weight. As we can see from Figure 1, there was little change in average birth weights, but placental weights fluctuated more markedly. In our paper, we show how these fluctuations may have been related to changes in real wage rates over the same period.
These findings support claims that the placenta is able to ‘adapt’ to changing economic circumstances, but our evidence also shows that such ‘adaptations’ may not be able to counteract the impact of maternal undernutrition entirely. As Figure 2 demonstrates, although most neonatal markers show a reverse J-shaped curve (a higher risk of perinatal mortality with premature or small-for-gestational-age births), the relationship between placental weight and early-life mortality is U-shaped.
We also control for maternal characteristics using a Cox proportional hazards model. Even if increases in placental weight can be regarded as a form of ‘adaptive response’, they are not cost-free, as both very low and very high placental weights are associated with increased risks of early-life mortality. These findings are consistent with David Barker’s conclusion that elevated placental weight ratios lead to adverse outcomes in later life (Barker et al. 2010).
We have also compared the average value of placental weights in the Provincial House with modern Spanish data. These data suggest that average placental weights have declined over the course of the last century. However, the data from other countries are more mixed. Placental weight also seems to have declined in Finland and Switzerland, but this is less obvious in other countries such as the United Kingdom and the United States.
Overall, whilst placental weights may well provide a sensitive guide to the intrauterine environment, we still know relatively little about the ways in which they may, or may not, have changed over time. However, this picture may change if more historical series come to light.
To contact the authors:
Gregori Galofré-Vilà, email@example.com, Twitter: @gregorigalofre
Bernard Harris, firstname.lastname@example.org
Barker, D. J. P., Thornburg, K. L., Osmond, C., Kajantie, E., and Eriksson, J. G. (2010), ‘The Surface Area of the Placenta and Hypertension in the Offspring in Later Life’, International Journal of Developmental Biology, 54, 525-530.
Burton, G., Jauniaux, E. and and Charnock-Jones, D.S. (2010), ‘The influence of the intrauterine environment on human placental development’, International Journal of Developmental Biology, 54, 303-11.
Galofré-Vilà, G. and Harris, B. (in press), ‘Growth Before birth: the relationship between placental weights and infant and maternal health in early-twentieth century Barcelona’, Economic History Review.
Kaur, D. (2016), ‘Assessment of placental weight, newborn birth weight in normal pregnant women and anaemic pregnant women: a correlation and comparative study’, International Journal of Health Sciences and Research, 6, 180-7.
O’Brien, O., Higgins, M. and Mooney, E. (2020), ‘Placental weights from normal deliveries in Ireland’, Irish Journal of Medical Science, 189, 581-3.
Roberts, E., and Wood, P. (2014), ‘Birth weight and adult health in historical perspective: Evidence from a New Zealand Cohort, 1907-1922’, Social Science and Medicine, 107, 154-161.
Schneider, E. (2017), ‘Fetal health stagnation: have health conditions in utero improved in the US and Western and Northern Europe over the past 150 years?’, Social Science and Medicine, 179, 18-26.
Wells, J.C.K. (2016), The metabolic ghetto: evolutionary perspectives on nutrition, power relations and chronic disease, Cambridge: Cambridge University Press.