<p>Extreme temperature events have become more frequent due to industrialization, urbanization, and climate change, leading to health risks. Women with twin pregnancies are particularly vulnerable, yet research on how these temperatures affect gestational diabetes mellitus (GDM) remains limited. This study investigates the impact of extreme temperatures on GDM incidence in twin pregnancies, focusing on identifying critical periods of susceptibility. Data from 3,769 twin pregnancies were analyzed using temperature information from local meteorological stations. Extreme temperatures, defined as heat waves and cold spells, were categorized by daily maximum, minimum, and mean temperatures. The relationship between the frequency and duration of these events and GDM risk was evaluated through multivariable logistic regression, while a distributed lag nonlinear logistic model assessed temperature impacts across gestational weeks. Results from 1,063 GDM cases revealed significant differences in incidence across screening temperatures. GDM risk increased with days exceeding the 90th percentile temperature in the four weeks prior to screening, as well as with the frequency of cold spells and heatwaves earlier in pregnancy. Both high and low extreme temperatures during specific gestational weeks were associated with higher GDM risk, suggesting these factors should be considered in preventive strategies for twin pregnancies.</p>