Introduction:
Caesarean section (CS) is the most common medical procedure performed in women all over the world. There is a hypothesis that caesarean section changes DNA methylation, and it has been linked to immune-mediated diseases such as diabetes in late infant health outcomes. The aim of the study was to evaluate the relationship between caesarean section and DNA methylation patterning in the placenta by measurement of global DNA methylation.

Material and methods:
We included in the study 111 healthy, pregnant women in singular pregnancy at term of delivery (gestational age at least 37 weeks). The study involved global methylation in placental tissue from 46 pregnant women, delivered by vaginal route, and 49 pregnant women, delivered by elective caesarean section (ECS) before the start of labour. In 16 of the elective caesarean section cases, regular uterine contractions were declared. An ELISA-based kit was used for an assessment of the global DNA methylation.

Results:
Global DNA methylation in the placenta in elective caesarean sections (3.02 on average) was significantly lower compared to intrapartum caesarean sections (3.71 on average) and vaginal deliveries (3.64 on average), but did not significantly differ between intrapartum caesarean sections and vaginal deliveries. Global DNA methylation in the placenta in male newborns was significantly higher (4.86 on average) than in female newborns (3.31 on average) in vaginal deliveries but not in either elective or intrapartum caesarean sections.

Conclusions:
Caesarean sections performed without uterine contractions significantly influenced global DNA methylation in the placenta. Moreover, a sexual dimorphism at the level of placental global DNA methylation was demonstrated. Further studies investigating different panels of genes may help to identify genes with aberrant methylation in newborn infants delivered by caesarean section compared to vaginal delivery, as well as demonstrate sexual dimorphism.