Objective <p>Sleep is fundamental to the physical and mental health of both the general population and pregnant women. Most studies have focused on the impact of certain trimester sleep behaviors on gestational complications and birth outcomes. This study aimed to explore the association between maternal sleep duration and fetal growth development from as early as 23 gestational weeks to birth.</p> Methods <p>A total of 803 pregnant women were prospectively enrolled. The self-reported maternal nocturnal sleep duration during all 3 trimesters was recorded. The outcome measures were reference-population-based Z-scores of fetal biometric measurements obtained through routine ultrasonographic examination.</p> Results <p>Using multiple linear regression, a marginally significant negative association was observed between second-trimester sleep duration and second-trimester fetal head circumference (HC) and third-trimester fetal biparietal diameter (BPD). Then the associations of long sleep duration in each trimester with fetal biometry extreme values were evaluated. A significant impact of second-trimester long sleep duration on the second-trimester BPD below the 10th percentile of the reference population was observed. Longitudinal analysis reported similar results for BPD and HC.</p> Conclusions <p>Overall, a negative association between sleep duration and fetal biometric measurements was observed. Long sleep durations in the second trimester might negatively impact fetal growth, particularly brain parameters, including BPD and HC.</p>