Introduction: Accurate determination of gestation is very important in routine antenatal care. Gestation age is usually determined from the last menstrual period, which is unreliable due to recall bias and menstrual irregularities etc. It is also determined from fetal biometry whose accuracy decrease with increasing gestation age. Normal placental growth determines normal fetal growth. Aim: To determine the average sonographic placental thickness and its correlation with GA among low-risk singleton pregnant women 15 weeks to 36weeks attending antenatal clinic at Mbarara Regional Referral Hospital. Methods: This was a cross sectional study of 249 singleton low risk pregnant women with known first day of last normal menstrual period (LNMP) at 15 to 36weeks of gestation attending antenatal clinic at MRRH from June 2021 to September 2021. Ultrasound scanning was performed using GE logic V2 ultrasound machine with (3-5MHZ) convex probe. Placental thickness (PT) was measured perpendicular at umbilical cord insertion, fetal growth parameters (BPD, HC, AC and FL) were also determined. Statistical analysis was performed using STATA© 15.0 software). Mean placental thickness with standard deviation was calculated. Pearson’s correlation was applied to determine the correlation between placental thickness (PT) and gestational age as well as foetal growth parameters. Results: In this study the participants age range was 16-43 years with mean of (25±5.59) years. Their parity ranged from 0-7(mean 1.28±1.37). The mean PT was (28.47 ± 5.43) mm. PT ranged from (17.95± 1.10) mm at 15 weeks to (37.50 ± 1.69) mm at 36 weeks. PT (in mm) had a linear relationship and a statistically significant positive correlation with GA (in weeks) (r = 0.96), p=0.001. There was also a statistically significant positive correlation between PT and the fetal growth parameters. Conclusion: Placental thickness increases with increase in gestational age. A strong positive correlation between PT and fetal ....