Secular changes in body height predict global rates of caesarean section

Abstract

The massive global variation in caesarean-section (C-section) rate is usually attributed to socio-economic, medical and cultural heterogeneity. Here, we show that a third of the global variance in current national C-section rate can be explained by the trends of adult body height from the 1970s to the 1990s. In many countries, living conditions have continually improved during the last century, which has led to an increase in both fetal and adult average body size. As the fetus is one generation ahead of the mother, the fetus is likely to experience better environmental conditions during development than the mother did, causing a disproportionately large fetus and an increased risk of obstructed labour. A structural equation model revealed that socioeconomic development and access to healthcare affect C-section rate via multiple causal pathways, but the strongest direct effect on C-section rate was body height change. These results indicate that the historical trajectory of socio-economic development affects-via its influence on pre-and postnatal growth-the intergenerational relationship between maternal and fetal dimensions and thus the difficulty of labour. This sheds new light on historic and prehistoric transitions of childbirth and questions the World Health Organization (WHO) suggestion for a global 'ideal' C-section rate. BackgroundCompared with other mammals, childbirth in humans is strikingly difficult owing to the tight fit between the baby's head and shoulders and the mother's pelvis [1][2][3][4][5]. United States (US) statistics suggest that cephalopelvic disproportion-a mismatch of the fetal head and the maternal birth canal-occurs in 2.3% of infants weighing 3-4 kg at birth and in 5.8% of those weighing more [6]. A number of individual risk factors for cephalopelvic disproportion have been identified, including maternal and paternal body height, obesity and the age of the mother [7][8][9][10][11][12][13][14]. In most countries, however, the rate (i.e. incidence) of caesarean section (C-section) greatly exceeds that of actual anatomical disproportion [15][16][17]. Even if the birth canal can accommodate the fetus, a tight feto-pelvic fit can delay labour and increase the risk of maternal and fetal morbidity, which is often prevented by caesarean intervention. C-section rates have been reported to correlate also with psychological factors such as fear and anxiety, socio-economic factors such as family income and education, as well as with access to healthcare [18][19][20][21][22][23]. As a result, C-section rate varies considerably across social and demographic groups within most countries. At a global level, C-section rate varies even more starkly, ranging from 1-2% in many sub-Saharan African countries, up to about 50% in Egypt, Turkey or Brazil. Even in Europe, which is culturally and socio-economically relatively homogeneous, incidences range from about 15% in Scandinavia to more than 35% in Portugal, Romania and Italy [16,17]. Especially in developing countries, incidences are rising rapidly [16,...

Obstetric dimensions of the female pelvis are less integrated than locomotor dimensions and show protective scaling patterns: Implications for the obstetrical dilemma

“…These findings carry implications for modern obstetric ease. At an individual level, most obstetric evidence suggests that shorter women experience a higher frequency of cephalopelvic disproportion (Liselele, Boulvain, Tshibangu, & Meuris, 2000; Mahmood, Campbell, & Wilson, 1988; Tsu, 1992) and caesarean section (Mahmood et al, 1988; Sheiner, Levy, Katz, & Mazor, 2005; Toh‐Adam, Srisupundit, & Tongsong, 2012; Wells, 2017), even if secular trends of increasing height are associated with greater frequency of caesarean section worldwide (Zaffarini & Mitteroecker, 2019). Since height factors into obstetric ease, allometric patterns, too, should account for height, especially among populations with small‐statured mothers (Takamuku, 2019).…”

Evolution of the human pelvis and obstructed labor: new explanations of an old obstetrical dilemma

“…Such environmental mismatch between maternal and fetal development adds to the increased frequency of cephalopelvic disproportion in countries recovering from famine or experiencing rapid socioeconomic development. 94 The evolutionary pressures that once increased the frequency of cephalopelvic disproportion have now been reduced by increased access to neonatal care and treatment of pelvic floor disorders, promotion of the survival of neonates, and the higher rate of preterm neonates with a lower birthweight and of women with a weak pelvic floor. These factors, in turn, reduce selection toward larger fetuses and narrower pelves.…”

Caesarean section delivery and childhood obesity in a British longitudinal cohort study

“…Studying the associations underlying the role of CS with childhood obesity is important, given the global increase in CS rates and the epidemic of childhood obesity. [28–30] We recently performed two studies[10, 31] to address some of the limitations of previous reports, but both studies only followed-up offspring to age five years.…”