Prediction of Growth Restricted Fetuses usingFemur Length to Mid-thigh Circumference Ratio: A Case-control Study

Abstract

Summary I ntrauterine growth restriction (IUGR) is etiologically associated with maternal, fetal and placental disorders. From a statistical viewpoint, the term "small for gestational age" (SGA) has been used to define newborns whose birth weights falls below the 10th percentile of gestational age specific birth weight standards. This definition has been useful for providing a better understanding of perinatal outcomes. However, the widespread use of ultrasound in obstetrics has changed the traditional way of looking at fetal growth during pregnancy and specific intrauterine growth charts have been developed. Sonographic measurements of fetal ultrasound parameters are the basis for accurate determination of gestational age and detection of fetal growth abnormalities. Selection of the most useful single biometric parameter depends on the timing and purpose of measurement and is influenced by various factors. The aim of this study was to evaluate the accuracy and usefulness of measuring femur length to mid-thigh circumference ratio in prediction of growth restricted fetuses by ultrasound in the third trimester of pregnancy. This case control study was conducted at the Department of Obstetrics and Gynecology, Faculty of Medicine, Ain Shams University.100 pregnant females were enrolled in this study and they were divided into 2 groups: Normal growth fetuses group: included 50 pregnant females with normal fetuses. IUGR foetuses groupincluded 50 pregnant females in the third trimester with intrauterine growth restricted fetus (IUGR). Gestational age was determined for all patients by early ultrasound measurements of CRL within 7 to 10 wks gestation. All women were either primipara (18% vs. 24%) or multipara (82% vs. 76%) with no statistically significant difference between parity in both study groups. Also there were no statistically significant difference between maternal age (27.92 +/- 4.0043 vs. 27.89 +/- 4.8592, BMI (27.18 +/-3.999 vs. 27.87+/- 3.8) and gestational age (34.76+/- 2.552 vs. 35.6+/- 2.07) (p˃0.005) in both study groups which indicates that both study groups were homogenous. In IUGR group most of women suffered from medical disorders (36% gestational HTN, 14% PE, 2% SLE) with a statistically significant difference (p<0.005). The actual birth weights were lower in growth-restricted fetuses than in normal fetuses (1697.6±495.8774 vs. 2057.2±1019.924, P <0.01). In IUGR group, AFI was significantly decreased (3.3+/- 1.908 vs. 11.98+/-2.2632) and umbilical artery Doppler ultrasound (RI) significantly increased (0.745+/-0.075 vs. 0.611+/-0.0791) and when compared with the normal group this showed statistically significant difference (p<0.005) as shown in which further prove the diagnosis of IUGR fetuses. The current study also showed that there was no significant difference between BPD (7.93+/-0.84 vs.7.73+/-0.63, p˃0.05), HC (29.26+/-2.3 vs. 28.55+/-2.207, p˃0.05), and FL (6.3256+/-0.686 vs. 6.207+/-0.5898, p˃0.05) in both study groups. However there was a significant decrease of MTC in IUGR group (8.9018+/-2.272p8 vs. 12.0492+/- 1.7319, p < 0.005) and AC (29.012+/-2.95 vs. 26.57+/-2.57, p<0.005).There was significant increase of HC/AC ratio in IUGR fetuses group (1.0517+/- 0.109 vs.0.9696+/- 0.120, p<0.005). There was a significant increase in FL/MTC ratio in IUGR group with cutoff point value 0.58. This ratio has sensitivity 82%, specificity 78%, positive predictive value 78.8%, negative predictive value 81.3% and 80% efficacy. It also showed that there was no correlation between FL/MTC and actual birth weight in both groups in spite of significant increase between FL/MTC ratios in the IUGR group (0.7027+/-0.193 vs. 0.5348+/- 0.094, p<0.005).