Background In obstetric and gynecologic practices, synchronous telehealth services via chat message, voice calls, and video calls have been increasingly equipped to improve patients’ health care accessibility and clinical outcomes. Nevertheless, differences in clinical outcomes between communication tools remain unknown, especially in terms of safety. Objective This study compared the occurrence of emergency visits and hospitalization after telehealth services through different communication tools, including chat messages, voice calls, and video calls. Methods We collected data on obstetric and gynecologic concerns of women who consulted specialized doctors and midwives through a telehealth consulting service in Japan (Sanfujin-ka Online) between January 1, 2019, and December 31, 2020. The outcomes were emergency visits or hospitalizations at night after the consultation. Chi-square test and multivariate logistic regression analysis were performed to compare the clinical outcomes between the groups who received telehealth services via chat message, voice calls, and video calls. Results This study included 3635 participants. The mean age of the participants was 31.4 (SD 5.7) years, and the largest age group (n=2154, 59.3%) was 30-39 years. The numbers (or proportions) of those who received telehealth services via chat message, voice calls, and video calls were 1584 (43.5%), 1947 (53.6%), and 104 (2.9%), respectively. The overall incidence of the outcome was 0.7% (26/3635), including 10 (0.3%) cases of chat message, 16 (0.5%) cases of voice calls, and no video calls. There were no emergency visits that happened due to inappropriate advice. No significant difference in the proportions of the outcomes was observed between the communication tools (P=.55). The multivariate logistic regression analysis showed no significant differences in the outcome between those who used chat message and those who used voice calls (odds ratio 1.63, 95% CI 0.73-3.65). Conclusions The communication tools of telehealth services in obstetrics and gynecology did not show a significant difference in terms of emergency visits or hospitalizations after using the service.