<p>Given the importance of carbohydrates during pregnancy and the limited evidence on the impact of its excessive intake on offspring neurodevelopment, this study aimed to assess the associations between maternal glycemic index (GI) and glycemic load (GL) during early and late pregnancy and behavior problems in 4-year-old children, considering potential sex-related differences in susceptibility to maternal diet. This observational study included 188 mother–child pairs from the ECLIPSES study. GI and GL were estimated from a validated food frequency questionnaire. Offspring behavior was assessed using the Child Behavior Checklist 1.5–5. Multivariable linear and logistic regression analyses were employed to assess the association between GI, GL, and child behavior. Children of mothers in the highest tertile of GL during the first trimester of pregnancy showed elevated scores of both internalizing (<i>β</i> = 5.77; 95% CI, 2.28–9.26) and externalizing (<i>β</i> = 3.95; 95% CI, 0.70–7.19) problems, including anxiety and depression problems, withdrawn, attention problems, aggressive behavior, and attention-deficit/hyperactivity problems, as well as total (<i>β</i> = 5.24; 95% CI, 1.71–8.77) and autism spectrum problems (<i>β</i> = 3.30; 95% CI, 1.11–5.50). Similarly, higher odd ratios were observed for internalizing (OR = 2.37; 95% CI, 1.09–5.18), externalizing (OR = 3.46; 95% CI, 1.49–8.00), and total problems (OR = 3.83; 95% CI, 1.68–8.71). These associations were more pronounced in girls. No associations were observed during the third trimester. Regarding GI, no associations were found for the evaluated outcomes in any of the trimesters. </p><p><i>Conclusion</i>: These findings indicated that elevated maternal GL during the early pregnancy, but not later stages, was associated with adverse behavioral outcomes in offspring.</p><p><i>Trial registration</i>: EUCTR-2012–005480-28, NCT03196882.</p><p><Table Float="No" ID="Taba"> <tgroup cols="1"> <colspec align="left" colname="c1" colnum="1" /> <tbody> <row> <entry align="left" colname="c1"> <p><b>What is Known: </b></p> <p>• <i>Carbohydrate intake is important during pregnancy as glucose is the main energy source for an optimal fetal brain development.</i></p> <p>• <i>Elevated prenatal glycemic index and glycemic load have been associated with adverse offspring outcomes but their impact on behavioral development remains insufficiently explored.</i></p> </entry> </row> <row> <entry align="left" colname="c1"> <p><b>What is New:</b></p> <p>• <i>A high maternal glycemic load during pregnancy may increase the risk of behavioral impairments in preschool-aged offspring.</i></p> <p>• <i>Female offspring may be more vulnerable to behavioral disturbances to elevated maternal glycemic load during gestation.</i></p> </entry> </row> </tbody> </tgroup> </Table></p>