Evaluation of ultrasonographic fetal kidney length for gestational age detection in late second and third trimesters

Accurate estimation of gestational age is necessary to obtain materials for different tests as well as to interpret the results of these tests.Unfortunately sometimes calculation of EDD based on LMP becomes very difficult when (a) The menstrual cycle is irregular; (b) Patient fails to remember LMP or reports inaccurately (c) Pregnancy occurs during lactational amenorrhoea & (d) if patient have bleeding in early pregnancy. After 24 weeks the symphysio-fundal height in cm. approximates to the number of weeks up to 36 weeks of gestation. But a number of factors influence the measurement including multiple gestation, IUGR, diabetic pregnancy, maternal size, variation in fetal lie & engagement as well as inter & intra observer measurement variation.Ultrasonic measurement of fetal biometry (CRL, BPD, FL) are considered to be reliable when they are performed in first & early 2nd trimester (<24 weeks). In this study, we aimed to evaluate the accuracy of ultrasonographic fetal kidney length measurement as a new parameter for estimation of gestational age in late second and third trimester in correlation to other commenly used parameters as, BPD, FL, AC. This study was conducted on 122 pregnant women attending antenatal care clinics of Obstetrics and Gynecology department Soliman Fakeeh Hospital, KSA. All were in the late second and third trimester (between 24-40 weeks) of gestation. Cases included in the study were divided into four gestational age groups with four weeks interval. The length of the fetal kidney was measured. The mean gestational age was calculated on the bases of biparietal diameter (BPD).femur length (FL) and abdominal circumference (AC). The fetal kidney measurements were obtained by the same sonographer to avoid interobserver variation using (GE machine E8) and were compared with gestational age using statistical analysis No statistically significant differences were found between the right and the left renal measurements in cases in which the two kidneys were imaged In this study, during the second and third trimester the mean kidney length showed gradual rate of increase. the mean kidney length was found to be 30.52.1 mm at mean gestational age of 26weeks and became at the mean gestational age of34 weeks, 40.4103 mm(:(±1.98) and at mean gestational age of 38 week it measured44.41mm((±2.1). In addition, we found a positive correlation between kidney length and gestational age. We suggested regression Formula to calculate it. Conclusion: Throughout this study, we can conclude that Fetal kidney length could be used with accuracy in the late second and third trimester especially in women who are uncertain of date of LMP and are booked late for ANC.however its accuracy is decreased when we use it in late third trimester.Other ultrasonographic parameters used for estimation of the gestational age as BPD ,AC are less satisfactory ,when compared with femur length and kidney length.