Objective: ADHD symptoms can adversely impact functioning in a range of domains relevant for maternal well-being and fetal development; however, there has been almost no research examining their impact during pregnancy. We aimed to address this gap. Method: We used data (n = 1,204) from a longitudinal birth cohort study spanning eight countries to address this gap. Results: ADHD symptoms in the third trimester of pregnancy were associated with lower social support from family (b = -0.16, p = 0.031), friends (b = -0.16, p = 0.024), and significant others (b = -0.09, p = 0.001); higher stress (b = 0.34, p < 0.001) and depressive symptoms (b = 0.31, p < 0.001), and increased likelihood of an unwanted pregnancy (b = 0.30, p = 0.009). Significant associations with tobacco use (b = 0.36, p = 0.023) and premature birth (b = 0.35, p = 0.007) did not survive correction for multiple comparisons and there were no significant associations with alcohol use, low birth weight, or unplanned pregnancy. Conclusion: Results suggest that women with ADHD symptoms could benefit from earlier, more regular screening for mental health difficulties and greater mental health support during pregnancy.