Predicting fetal intrauterine growth retardation by using reference centile charts for the ratio of fetal transverse cerebellar diameter to abdominal circumference in a Thai population.

ABSTRACT

Objective: To predict fetal intrauterine growth retardation (IUGR) by using the centile chart for the ratio of transverse cerebellar diameter to abdominal circumference (TCD/AC) throughout pregnancy from 13-40 weeks. Methods: A total of 643 pregnant women were recruited in this study. The exclusion criteria of 643 normal pregnant women were uncertain date of last menstrual period, multiple pregnancies, fetal abnormalities and maternal conditions which could affect fetal growth. The known 20 small IUGR infants were also tested. Transverse cerebellar diameter and abdominal circumference of all the subjects were measured out by gestational age. The approximately equal numbers of fetuses were measured at each week of gestation. The mean and standard deviation of TCD/AC ratio is estimated at each week of gestation. In addition the 5th, 10th, 50th, 90th and 95th percentiles were calculated at each week of gestation. Results: Of 643 pregnant women, 149 (23.1%) were scanned before 20 weeks of gestation and 286 (44.5%) were scanned between 20 and 30 weeks of gestation. The last group was rechecked after 30 weeks of gestation. TCD/AC ratio slowly declined from early pregnancy until about 20 weeks then remained stable. After 30 weeks of gestation it started to decline again. A TCD/AC ratio greater than the 90 th centile was present in 80% (16/20) known small for gestational age (SGA) infants. (SGA has not been defined). Conclusion: The normal reference value of TCD/AC ratio in Thai fetus were shown in this study. The TCD/AC ratio is a stable, gestational age independent parameter during 20-30 weeks of gestation that may be useful in the early detection of fetal intrauterine growth retardation (IUGR).