Comparison between Taans Cerebellar Diameter, Biparietal Diameter and Femur Length for Gestational Age Measurement Accuracy in The 3rd Trimester

Backgound: the provision of obstetric and neonatal care, as well as the public health monitoring of pregnancy outcomes, relies upon the accurate determination of gestational age. Uncertain gestational age has been associated with adverse pregnancy outcomes including low birth weight, preterm delivery and perinatal mortality, independent of maternal characteristics. Many patients in Egypt due to socio-economic reasons come for their first antenatal visit in the third trimester. Most of them are uneducated and come from remote areas. Also, many being lactating mothers are unsure of their LMP or have irregular cycles. Because of non availability of any dating scans or earlier ultrasound and uncertainty in LMP, it becomes very difficult to calculate their due dates, so many pregnancies considered to be preterm or posterm were wrongly classified. The use of ultrasonography has significantly improved evaluation of fetal growth and development and had permitted prenatal diagnosis of a variety of congenital malformations. Ultrasonographic fetal biometry is highly reliable in the first and second trimester of pregnancy, but reliability of any ultrasound method greatly diminishes as gestational age advances, in the third trimester, reliability of any single ultrasound parameter alone is poor without correlation with other parameters.Objective: in our study, TCD was compared to FL and BPD in accuracy of assessment of gestational age in the third trimester of pregnancy. We correlated between the three parameters, Transcerebellar (TCD) and Biparietal diameter (BPD) and Femur length (FL), for accurate determination of gestational age in third trimester of pregnancy. Methods: a total of 200 pregnant women in the third trimester pregnancy was assessed in this observational study in Department of Obstetrics and Gynecology, Damietta Hospital, Al-Azhar University (Outpatient) by two-dimensional ultrasound to assess the accurate method for assessment of gestational age in the third trimester of pregnancy. Examinations were performed after a verbal consent from the patient with the patient lying in the dorsal supine position. Two dimensional ultrasounds were carried out. Fetal biometry and amniotic fluid volume were assessed. All women included in this study were subjected to history taking and clinical examination.Results: we found that out of 200 patients, TCD gave correct assessment of gestational age within 3 days in 118 patients (59%) and within 1 week in 180 patients (90%). While, FL gave correct assessment of gestational age within 3 days in 92 patients (46%) and within 1 week in 160 patients (80%). The least accurate was BPD that gave correct assessment of gestational age within 3 days in 59 patients (29.5%) and within 1 week in 120 patients (60%). Conclusion: from this study, we concluded that TCD was the most accurate method for assessment of gestational age in the third trimester followed by FL and the least accurate was the BPD. Also, by combining accuracy of TCD (90%) and that of FL (80%) we can be near certain of gestational age in most of our patients even if they are unsure of their dates. Recommendations: measuring TCD as routine in the third trimester as it has the same accuracy as the current fetal biometry (BPD and FL).