Background: At the turn of the 20th century, women commonly died in childbirth due to "rachitic pelvis". Although rickets virtually disappeared with the discovery of the hormone "vitamin" D, recent reports suggest vitamin D deficiency is widespread in industrialized nations. Poor muscular performance is an established symptom of vitamin D deficiency. The current US cesarean birth rate is at an all-time high of 30.2%. We analyzed the relationship between maternal serum 25-hydroxyvitamin D [25(OH)D] status, and prevalence of primary cesarean section.

Methods: Between 2005 and 2007, we measured maternal and infant serum 25(OH)D at birth, and abstracted demographic and medical data from the maternal medical record, at an urban teaching hospital in Boston, USA, with 2,500 births per year. We enrolled 253 women, of whom 43 (17%) had a primary cesarean.

Results: There was an inverse association with having a cesarean section and serum 25(OH)D levels. We found that 28% of women with serum 25(OH)D <37.5 nmol/L had a cesarean section, compared to only 14% of women with 25(OH)D 37.5nmol/L (p=0.012). In multivariable logistic regression analysis controlling for race, age, education level, insurance status, and alcohol use, women with 25(OH)D <37.5 nmol/L were almost 4 times as likely to have a cesarean than women with 25(OH)D 37.5 nmol/L (AOR 3.84; 95% CI 1.71 to 8.62).

Interpretation: Vitamin D deficiency was associated with increased odds of primary cesarean section.