Association Between Digit Ratio and Postoperative Nausea and Vomiting: A Single-Center Prospective Cohort Study

Postoperative nausea and vomiting (PONV) occurs even with preventive measures. Several reports suggest that PONV is associated with sex hormones. However, estimating individual hormone levels remains challenging. The digit ratio, the length ratio of the second to the fourth fingers, is a noninvasive predictor of hormone levels, with a ratio ≥ 1 being more feminine. We investigated whether digit ratio predicts PONV.

This single-center prospective study included patients aged > 18 years who underwent general anesthesia for scheduled surgery at the Jichi Medical University Saitama Medical Center. PONV prophylaxis was administered according to the number of risk factors defined by the well-established Apfel simplified risk score (female, nonsmoking, history of motion sickness or PONV, and postoperative opioid usage). The primary endpoint was PONV incidence within 24 h postoperatively, stratified by the digit ratio. As a subgroup analysis, we analyzed the impact of the digit ratio on the incidence of PONV, which was further categorized according to sex, age, and type of surgery. Univariable and multivariable logistic regression analyses were also conducted to identify the risk factors associated with PONV.

Overall, 792 patients were included, with 19.1% having a digit ratio ≥ 1 and 80.9% < 1. Significant differences were observed in sex and age between the groups. PONV incidence within 24 h was 18.5% in the digit ratio ≥ 1 group and 18.7% in the digit ratio < 1 group, with no significant difference. Subgroup analyses by sex and younger age also showed no significant differences, except for a higher PONV incidence in abdominal surgery patients with digit ratio ≥ 1. Regression analysis identified the Apfel simplified risk score as a significant risk factor for PONV.

Digit ratio was not associated with PONV in the overall patient population. However, an association was found in patients who underwent abdominal surgery, suggesting that digit ratio might be a risk predictor in this subgroup. Future studies should focus on larger sample sizes of patients undergoing high-risk surgeries to validate these findings. Trial Registration: University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR); UMIN000048615.