Placental thickness & its correlation to gestational age & foetal growth parameters- a cross sectional ultrasonographic study

Abstract

Background: The Gestational Age (GA) is frequently over or under estimated, as the conventional gestational estimation is based on the Last Menstrual Period (LMP) and on ultrasonography (USG). Many people are unaware of their LMP and irregular menstruations and USG is bound to have a bias, thereby posing difficulties in the GA estimation.

Aim: This study was aimed at estimating the (Placental Thickness) PT and at investigating the relationship between PT and the foetal growth parameters in normal singleton pregnancies.

Materials and methods: Two hundred eleven pregnant women were recruited in a cross sectional prospective study. The pregnancies were between 11 to 40 weeks and they were not complicated by either maternal or foetal diseases. The Biparietal Diameter (BPD), the Abdominal Circumference (AC), the Head Circumference (HC), the Femur Length (FL) and the PT were measured by USG by using a 3.5 MHz transducer.

Results: The maximum mean PT in the 1st, 2nd, 3rd and the combined trimesters were 16.5 mm, 23.78 mm, 35.81 mm and 28.49 mm respectively. The correlation between PT and the other foetal parameters was investigated by Pearson's correlation analysis. The values were expressed as mean + standard deviation. The statistical tests were two-tailed, with a p value of < 0.01, which indicated the statistical significance. There was a strong positive correlation between PT and GA, with the correlation coefficient values for the 1st, 2nd and 3rd trimesters being r = 0.609, r = 0.812 and r = 0.814 respectively. There was a significant positive correlation between PT and BPD, AC, FL, ABC, HC and FW also. The mathematical relationships between PT and GA, BPD, AC, FL, ABC, HC, FW were derived by regression analysis. The regression equation which was derived was (x - 22.92) = (0.3604) (w-27.86446) + (1.0256)(y-1.1678) + (0.0015)(z-216.2841) + (0.1047) (t-43.1555) + (0.027) (u.192.79000) + (0.0042) (v-60.3725), where x = GA in weeks, w = PT in mm, y = FW in kg, z = HC in mm, t = FL in mm, u = AC in mm and v = BPD in mm.

Conclusion: We conclude that PT can be used as a predictor of the GA. The subnormal PT for the corresponding GA should be evaluated for any disease condition. So, the measurement of PT should therefore be carried out routinely during the obstetric USGs.

Keywords: Gestational age; Last menstrual period; Placental thickness; Ultrasonography.

[Table/Fig-5]:

Shows correlation values distribution between PT & GA in 211 subjects.