Nutrition during pregnancy: the good nutritional status of the mother favors the growth of the fetus causing the increase in cases of cesarean section

The gradual improvement in maternal nutrition over recent years could be behind the increasing number of women giving birth via cesarean section. The good nutritional status of mothers seems to promote the development of a fetus too large for natural delivery. This theory could explain the huge gap in cesarean rates across different parts of the world, and it is also supported by the rising number of cesareans in developing countries.

These are the findings of a study conducted by a team of researchers from the University of Vienna, published in Proceedings of the Royal Society B.

Cesarean section rates: huge differences across countries

Although the WHO (World Health Organization) has suggested an ideal cesarean rate between 10% and 15%, the current frequency of this type of delivery varies among social and demographic groups, ranging from 1% to 2% in many sub-Saharan African countries, up to about 50% in Egypt, Turkey, and Brazil. In developing countries, the incidence is also rising rapidly. In Europe, rates range from about 15% in Scandinavia to over 35% in Portugal and Romania. In Italy, cesarean births have increased significantly over the last twenty years, rising from 11.2% in 1980 to 33.2% in 2000, with substantial differences among regions. Despite differences in obstetric practices, healthcare systems, and dietary habits, the variation in cesarean rates remains puzzling. Some studies have highlighted the tendency of obese mothers to give birth to very large newborns and an increased risk of fetopelvic disproportion—when the maternal pelvic diameter is smaller than the fetal head diameter. According to some studies, women exposed to malnutrition during childhood and early adulthood, characterized by short stature and a narrow pelvic canal, who later adopt a high-calorie diet during pregnancy, give birth to large babies, facing serious risks during labor due to fetopelvic disproportion. A high-calorie diet also affects the balance between maternal and fetal metabolism and may lead to prolonged gestation, with higher risks of post-term birth and obstetric complications.

Data confirm the relationship between maternal physical condition and newborn size

The research team linked maternal nutrition to differences in cesarean rates, discovering that proper nutrition can contribute to the development of a disproportionately large fetus.

"Since the fetus represents a generation ahead of the mother, on average it experiences environmental conditions even more acutely," stated co-author Philipp Mitteröcker, evolutionary biologist at the University of Vienna.

Paradoxically, then, environmental improvements in recent decades may make natural births more difficult and thus increase cesarean deliveries, because on average fetuses are larger than optimal for natural birth.

The scientists hypothesized that changes in recent decades may have influenced the number of cesarean births across countries. The mechanism by which environmental and nutritional factors influence maternal and fetal body size is well documented by numerous scientific studies.

Study details

During the research, the Viennese authors began examining global data on national cesarean rates and adult height variations of people born between 1896 and 1996. Cesarean percentages were estimated for the period 2005 to 2017; women giving birth during this time were born between the 1970s and 1990s. The cesarean rate was calculated as the total number of cesarean births divided by the total number of live births. Results indicated that environmental changes had a strong effect on the average increase in body height, established at about one millimeter per year; and that this could cause a roughly 10% increase in cesareans. Growth in body size was typical in many countries during the 19th and 20th centuries and still occurs in many emerging countries. The team also collected data on national obesity and diabetes rates and average maternal age at first birth, all known to influence labor outcomes at the individual level. According to the researchers, this not only explains part of the increase in cesarean deliveries in many countries but also sheds new light on historical birth transitions and challenges the WHO recommendation of an ideal cesarean rate between 10% and 15%.

Socio-economic development influences cesarean rates

The study’s results highlight the need for a more differentiated view that better considers differences among geographic and social groups. According to the findings, socio-economic development and access to healthcare affect cesarean rates through multiple mechanisms, but the strongest direct effect appears to be the average increase in stature. These results indicate that the history of socio-economic growth influences prenatal and postnatal growth, the relationship between maternal and fetal size, and thus labor difficulty. The study therefore encourages a paradigm shift away from purely cultural explanations of cesarean rates toward a combined biological and cultural perspective that includes sociocultural transitions, human anatomy, and physiology.

Source: Eva Zaffarini and Philipp Mitteroecker “Secular changes in body height predict global rates of caesarean section.”; Proceedings of the Royal Society B