Relationship between Placental Thickness and Gestational Age and Development of Novel Normative Percentile Charts and Table of Placental Thickness During Pregnancy: A Systematic Review

Background: This systematic review aimed to assess the correlation between placental thickness and gestational age, as well as to create normative reference tables and charts. We evaluated the association between placental thickness and gestational age from 12 to 40 weeks in normal singleton pregnancies. Methods: A thorough search of various databases was performed from inception to October 31, 2024, focusing on uncomplicated singleton pregnancies. A weighted mean of placental thickness was calculated weekly from the mean placental thicknesses obtained between the 12^th and 40^th weeks. Novel smoothed percentile charts were generated by applying z-scores to these weighted means, marking a standardized reference for placental thickness across gestation. Results: Our systematic review incorporated 20 eligible studies involving 7955 participants, with 3,601 observations between 12 and 27 weeks and 4354 observations between 28 and 40 weeks. There was a strong positive correlation (r = 0.95, 95% confidence interval: 0.93–0.98) between placental thickness and gestational age. Subsequently, we generated standardized normative percentile charts for clinical application, serving as a practical tool for estimating gestational age. Conclusion: These charts are particularly useful in limited resource settings, providing clinicians with a tool to estimate gestational age accurately.