# The Correlation of Fetal Kidney Length With Gestational Age From 24 Weeks of Pregnancy

## TL;DR

This study shows that fetal kidney length is a highly accurate measure for estimating gestational age in late pregnancy.

## Contribution

The study demonstrates that fetal kidney length has the strongest correlation with gestational age compared to other biometric indices.

## Key findings

- Fetal kidney length showed the strongest correlation with gestational age (r=0.981).
- Fetal kidney length had a standard error of 9.83 days in predicting gestational age.
- A model combining all five biometric indices achieved the highest accuracy (8.09 days).

## Abstract

Background

There has been an ongoing quest for a single ultrasonographic parameter to assess the accurate gestational age (GA) of the fetus that is unaffected by intrauterine growth restriction (IUGR). While fetal kidney length (FKL) is a parameter that can be used for dating late pregnancies, it has not been studied extensively as a biometric index for GA estimation. This study aimed to assess FKL in pregnancy from 24 weeks and its correlation with the GA of the fetus.

Materials and methods

We conducted a cross-sectional study in the Department of Obstetrics and Gynecology at Credence Hospital, Thiruvananthapuram, Kerala, India over six months. Ultrasounds were performed and mean FKL (average length of right and left kidney), biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) were measured by a single experienced sonologist.

Results

Among the five fetal biometric indices, we found that FKL displayed the strongest correlation with GA (r=0.981). FKL was also the most accurate parameter in predicting GA, with a standard error of 9.83 days. The most inaccurate one was head circumference, with a standard error of 14.05 days. The stepwise regression analysis showed that the most precise means of estimating GA was a model that included all five variables, with an accuracy of 8.09 days.

Conclusions

Our findings showed that by measuring FKL, pregnancies can be dated within 9.83 days among people who booked late or those who had forgotten the date of their last menstrual period.