Ginekologia i Poloznictwo
ISSN 1896-3315 e-ISSN 1898-0759

Evaluation of Fetal Kidney Length as an innovative sonographic parameter in the Second and Third Trimesters of Pregnancy to assess the Gestational Age Among Egyptian Antenatal Women: A Cross-Sectional Study

Mai Raafat Hussein¹, Noura Soliman Mohammed², Ihab Ibrahim Samaha¹, Hossam Elsayed Abdelmgeed¹ and Karim AbdelSalam^{1* *}Correspondence: Karim AbdelSalam, Department of Obstetrics and Gynecology, Faculty of Medicine, Helwan University, Egypt,

Received: 04-Nov-2024, Manuscript No. gpmp-25-161653; Editor assigned: 05-Nov-2024, Pre QC No. P-161653; Reviewed: 20-Nov-2024, QC No. Q-161653; Revised: 30-Nov-2024, Manuscript No. R-161653; Published: 30-Dec-2024

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Abstract

Background: Reducing postdate pregnancies improves maternal and fetal health and lowers complications, and accurate Gestational Age (GA) estimation is essential for this. In order to estimate Gestational Age (GA) in the second and third trimesters, this study sought to ascertain how accurate ultrasound is at measuring Fetal Kidney Length (FKL). The actual GA obtained from a reliable last menstrual period was compared with FKL along with other fetal growth measures such as Biparietal Diameter (BPD), Head Circumference (HC), Abdominal Circumference (AC), and Femur Length (FL).

Methods: The 58 pregnant women in this prospective observational study, who ranged in age from 18 to 40, GA between 20-40 weeks, singleton pregnancy, the last 3 cycles before pregnancy were regular and no hormonal contraception in the preceded 3 cycles. All patients were subjected to two-dimensional ultrasound examination.

Results: Gestational Age (GA) assessed via ultrasound in the second and third trimesters, Fetal Kidney Length (FKL), and the Last Menstrual Period (LMP) all showed a strong positive correlation. In addition, Biparietal Diameter (BPD), Femur Length (FL), Head Circumference (HC), and Abdominal Circumference (AC) were positively associated with GA. FL, BPD, and FKL were also found to be independent predictors of GA.

Conclusions: FKL can thus serve as an accurate tool for GA estimation late in the second and third trimesters.

Introduction

In order to reduce complications, improve maternal and fetal health and decrease postdate deliveries, it is crucial to accurately estimate Gestational Age (GA). It guarantees that treatments are administered at the appropriate time, preventing treatments from being started too soon or too late. [1].

Since early inductions are linked to higher failure rates and a higher incidence of surgical procedures, even in the early third trimester, properly estimating fetal age is essential to the success of labor induction in post-term pregnancies, accurate knowledge regarding pregnancy duration is critical for deciding on prenatal steroid prophylaxis for fetal lung maturation [2].

An accurate GA is critical for the identification of fetal development abnormalities and the time of elective delivery. For example, in fetal growth restriction determining the accurate GA is the corner stone for diagnosis and then managing the proper time of termination [3].

Femur Length (FL), Head Circumference (HC), Abdominal Circumference (AC), and Biparietal Diameter (BPD) are the four biometric indicators that should be used in pregnancies after 20 weeks in order to minimize variability. Although they lose their accuracy as the pregnancy goes on, these measurements has the power to predict the second trimester's Gestational Age (GA) with a reasonable degree of accuracy (± 10–14 days) [4].

In the third trimester, a number of ultrasound measurements, including Femur Length (FL), are used to determine Gestational Age (GA); however, their accuracy margin generally differs by two to three weeks from the GA itself [5].

Kidneys are one of the body's most important organs. Sonography can be used to identify renal abnormalities by measuring the length of the kidney. At 14 weeks of gestation, the kidney may be seen. The fetal kidney's visibility is improved as pregnancy progresses due to the buildup of perinephric fat and an increase in echogenicity, which help distinguish it from the surrounding soft tissues [6]. Fetal renal growth is greatest between weeks 26 and 34 of pregnancy; research shows that Fetal Kidney Length (FKL) increases in a linear fashion with Gestational Age (GA). Kidneys consistently grow by about 1.7 mm every two weeks, whereas embryonic kidneys grow by 1.07 to 1.1 mm per day [7].

Using the last menstrual period as a reference, this study sought to evaluate the accuracy of Fetal Kidney Length (FKL) as determined by ultrasound in estimating gestational age. It did this by comparing it to other growth parameters (femur length, head circumference, abdominal circumference, and biparietal diameter) during the second and third trimesters.

Patients and Methods

The 58 pregnant women in this prospective observational study, who ranged in age from 18 to 40, GA between 20 – 40 weeks, singleton pregnancy, the last 3 cycles before pregnancy were regular, no hormonal contraception in the preceded 3 cycles and available documented ultrasonography that had been done between 11 weeks and 14 weeks confirming the dates. The study from April 2023 and October 2023 was carried out with permission from the Helwan University Hospitals' Ethical Committee in Cairo, Egypt. The patients provided written, informed consent.

Exclusion criteria were hypertension with pregnancy, diabetes with pregnancy, multiple gestation, fetal growth restriction, fetal macrosomia, amniotic fluid abnormalities, congenital fetal malformation and abnormal fetal renal morphology.

Laboratory and radiological investigations, clinical examinations, and history taking were performed on every patient.

Two-dimensional ultrasound examination

Obstetric ultrasound was performed using (GE Logiq P5) ultrasound machine. BPD, FL, AC and HC were measured to confirm normal growth and calculate the estimated GA using Hadlock formula. Warm water-based gel was applied to the patient's abdomen while they were supine. Images for evaluating fetal presentation, cardiac activity, and number of fetuses, placenta location, amniotic fluid, and biometric measurements were obtained by adjusting the transducer. The biparietal diameter was measured using an axial plane at the level of the cavum septum pellucidum and thalami, which ranged from 2.4 cm at 13 weeks to 9.5 cm at term. The widest area of the abdomen, which includes the stomach, spine, umbilical vein, and liver, was used to measure the Abdominal Circumference (AC). To estimate fetal weight (EFW) and Gestational Age (GA), the Hadlock formula was combined with Head Circumference (HC) and Femur Length (FL). By positioning the probe to view both kidneys beneath the stomach, the length of the kidneys was determined.

The Fetal Kidney Length (FKL) of each patient was measured twice: once in the second trimester (weeks 20–26) and once in the third trimester (weeks 30–40). Then, using a formula that links kidney length in millimeters to Gestational Age (GA) in weeks, GA was calculated [8].

This GA was compared to GA calculated by LMP and confirmed by first trimester ultrasound, and to GA calculated by Hadlock formula in second and third trimester.

The ultrasound examination was done by 2 independent sonographers. To eliminate operator bias, one sonographer conducted the examination using only traditional biometric measurements, while the other was instructed to measure only Fetal Kidney Length (FKL).

The primary outcome measure was comparing GA calculated by FKL throughout trimesters two and three. to the GA calculated by LMP and first trimester ultrasonography. The secondary outcome was comparing FKL as a single parameter to FL, AC, BPD, and HC as single parameters and combined parameters in calculation of GA in late pregnancy.

Sample size calculation

Using PASS 2021 Power Analysis and Sample Size Software (2021). NCSS, LLC. Kaysville, Utah, USA, ncss.com/software/pass. A previous study reported that the mean ± SD FKL at 20-40 week of gestation age was approximately 30 ± 0.1 mm. The same study reported that the standard error of prediction (residuals standard deviation) was 9.048 days and the slope for the independent variable (X) was 70.12 [9]. Based on these assumptions, There is 99% statistical power to identify a shift in the slope from 0 (the null hypothesis) to 70 (the alternative hypothesis) in a sample of 58 pregnant women. A two-sided test was used for the analysis, with a significance level of P<0.001. The standard deviations for X and residuals were 0.1 mm and 9.048 days, respectively.

Statistical analysis

To conduct the statistical analysis, SPSS v26 was employed. While frequencies and percentages were used to summarize qualitative variables, means and standard deviations were used to summarize quantitative variables. Two quantitative variables were compared using Pearson's correlation test, with p<0.05 designated as the significance level.

Results

This table shows the demographic information and the Gestational Age (GA) determined by the fetal biometry in the second and third trimesters, the ultrasound in the first trimester, and the last menstrual period (Tab. 1.).

Tab. 1. The study patients' demographic details and Gestational Age (GA), which was determined by the last menstrual cycle, first trimester ultrasound, and fetal biometry in the second and third trimesters.

A strong positive correlation was found between Gestational Age (GA) from the last menstrual period and first-trimester ultrasound and GA based on femur length, abdominal circumference, head circumference, and biparietal diameter in the second and third trimesters (P=0.001) (Tab. 2.).

Tab. 2. GA determined by the patients' last menstrual cycle and first trimester ultrasound and GA determined by FKL and fetal biometry in the second and third trimesters.

Positive correlations were found between GA, AC, HC, BPD, FL, and FKL in both trimesters (P<0.05). The second trimester displayed the strongest correlations for GA, AC, HC, and FL with FKL, while in the third trimester, GA, HC, and AC showed the strongest correlations with FKL. Moderate correlations between BPD and FKL were observed in both trimesters (Tab. 3.).

Tab. 3. Correlation between GA calculated by FKL in the second and third trimesters and other GA calculated by fetal biometry parameters of the studied patients.

FL, BDP and FKL were independent predictor of GA at second and third trimester (P <0.001) (Tab. 4.).

Tab. 4. Linear regression of (FL, BDP and FKL) vs. GA at second and third trimester of the studied patients.

Discussion

GA is the duration of pregnancy beginning from the first day of the LMP. It is often estimated in weeks and days [10].

In our study, in the second trimester, the FKL ranged from 1.9 to 3.1 cm with a mean value (± SD) of 2.43 (± 0.29) cm. In the third trimester, the FKL ranged from 2.34 to 3.85 cm with a mean value (± SD) of 3.38 (± 0.29) cm. This agrees with Fathey, et al. [11] reported that the right kidney length ranged from 2.41 to 4.04 cm, with a mean of 3.4 ± 0.42 cm, and the left kidney length ranged from 2.43 to 4.25 cm, with a mean of 3.43 ± 0.41 cm. Fetal Kidney Length (FKL) ranged from 20.87 to 41.41 mm in the late second and third trimesters, with a mean of 32.18 ± 5.96 mm. According to Edevbie and Akhigbe [12] and Francis and Karunakaran [13], FKL grew by 1 mm every week, from 18.50 ± 2.10 mm at week 18 to 35.30 ± 1.60 mm at week 35. There was a notable increase between weeks 18 and 24.

According to our research, the average FKL rose from 2.43±0.29 cm in the second trimester to 3.38±0.29 cm in the third. This is corroborated by research showing that renal kidney length increases linearly over the course of the gestational weeks, as reported by Abonyi, et al. [14] and Al-Mlah, et al. [15].

During the second and third trimesters, there was a positive relationship between Gestational Age (GA) and Fetal Kidney Length (FKL), Femur Length (FL), Biparietal Diameter (BPD), Head Circumference (HC), and Abdominal Circumference (AC). This came in agreement with Fathey, et al. [11] revealed highly statistically significant correlations between the GA and the kidney length as well as the other established parameters. In agreement, Faraag, et al. [8] reported that the kidney length in their investigation was nearly identical to all of the ultrasound biometric parameters combined and showed a strong correlation with the assigned GA. Additionally, Kiridi, et al. [16] found that FKL increased linearly with GA. There was a 79% change in GA (ʼ2) for every unit change in mean kidney length.

Differences in ultrasonography technology or operator skill may be the cause of the variation in our study's standard error of estimate. This emphasizes even more how Fetal Kidney Length (FKL) can be used to estimate Gestational Age (GA). In order to prevent unfavorable feto-maternal outcomes, obstetricians must accurately estimate GA for pregnant women who present later or who have an unclear last menstrual period. While fetal biometric measurements like BPD, HC, FL, and AC become more accurate in later stages of pregnancy, crown-rump length (CRL) and gestational sac diameter are typically used to estimate GA in the early stages. Fetal Kidney Length (FKL), which has a strong correlation that validates its utility for GA estimation, has been shown to be more accurate than other biometric indices in the second half of pregnancy.

The study's limitations included the relatively small sample size. Only one center was used for the study. Only included women with reliable last menstrual period and normal pregnancies

Conclusion

In the second and third trimesters, our study found a significant positive correlation between GA and FKL, while BPD, HC, AC, and FL showed comparable patterns. The reliability of the mean FKL in estimating GA was demonstrated by its increase from 2.43 ± 0.29 cm at 20-26 weeks to 3.38 ± 0.29 cm at 26-40 weeks.

Funding

None.

Conflict of Interest

None.

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