Gestational age estimation is one of the most important information conveyed by a sonologist when performing an obstetric ultrasound examination. The traditional fetal biometric parameters, such as biparietal diameter (BPD), head circumference (HC), femur length (FL), and abdominal circumference become increasingly unreliable for accurate gestational age estimation with advancing pregnancy, especially in 3rd trimester. This study was conducted to assess the role of fetal kidney length (KL) as an alternate parameter to assess gestational age in 2nd and 3rd trimesters.

To assess relationship between sonographic gestational age and fetal KL between 18 and 39 weeks of gestation.

Prospective, cross-sectional, single operator study conducted over a period of 1 year in a medical college hospital.

Three hundred singleton pregnant women between 18 and 39 weeks of gestation were subjected to antenatal ultrasound. In addition to routine fetal biometry, measurements of fetal KL were made by noting distance between upper and lower poles of each kidney on a sagittal section of the fetal abdomen. The right and left KLs were averaged to obtain a single value for the purpose of statistical analysis.

Statistical analysis is done using SAS 9.2, SPSS 15.0, Stata 10.1, Med Calc 9.0.1, Systat 12.0, and R environment version 2.11.1. Fetal KL was expressed as mean ± standard deviation. Linear regression analysis was used to establish a relationship between sonographic gestational age in weeks and fetal KL. Level of significance was expressed as p value.

A strong statistical correlation was found between sonographic gestational age and fetal KL. Nomograms and growth curves were constructed to correlate gestational age with fetal KL.

Fetal KL measurements can be used as alternate method of estimating gestational age in women with uncertain last menstrual periods (LMPs) and presenting late in the gestation for safe confinement. In fetal macrocephaly, hydrocephalus, short-limb dysplasias, and when fetal head is engaged, these measurements are valuable alternate parameters to assess gestational age since they are simple, not time-consuming, easy to identify, and measure.

Hemraj S, Abraham SM, Acharya D, Ravichandra G, Vinayaka US. Sonographic Correlation of Gestational Age with Fetal Kidney Length. Int J Infertil Fetal Med 2016;7(2):37-41.