Estimation of Gestational Age by Using Fetal Kidney Length and Transcerebellar Diameter in Comparison with Other Biometric Indices

Introduction

When it comes to providing good maternity care, such as identifying developmental abnormalities and choosing the most optimal delivery time, obstetricians rely on precise gestational age (GA) determi-nations. Increased rates of prenatal mor-bidity and mortality have been asso-ciated with iatrogenic preterm delivery and postmaturity, which can occur as a result of failure ^(1).

In a typical 28-day menstrual cycle, the first day of the last menstrual period (LMP) is used to establish the pregnancy dates. But studies show that more than 30% of women either forget when their LMP was or mistakenly believe that bleeding during early pregnancy is typical menstruation ^{(2, 3).} Hormone treatment or rare ovulation can also cause ovulation to be delayed, which would explain why gestational age calculations throughout pregnancy are inaccurate. More accurate date assessment is now within reach, thanks to advancements in diagnostic ultrasono-graphy. Ultrasound measurements of the gestational sac's diameter, volume, and crown-rump length (CRL) can be taken during the first trimester of pregnancy to determine the gestational age (GA) ^(4,5). Additionally, during various stages of pregnancy, biometric markers such as fetal biparietal diameter (BPD), femur length (FL), and head circumference (HC) are used to estimate gestational age (GA) ^(6).

On the other hand, these indicators start to lose some of their accuracy in estimating gestational age as the pregnancy progresses ^(7). The unreliability of BPD measurements after 26 weeks of gestation is due to changes in cranial morphology caused by certain disorders, which limits these metrics. Achondroplasia patients have shorter femurs, making this an inaccurate measure of gestational age^(8). The measure-ements of biparietal diameter (BPD), head circumference (HC), femur length (FL), and abdominal circumference (AC) can be affected by a number of factors. These include abnormal positionning of the baby (breech presentation), low or high levels of amniotic fluid (polyhydramnios), multiple pregnancies, and intrauterine growth restriction (IUGR). Knowing the exact gestational age throughout the second and third trimesters is thus still challenging. In order to find the gestational age (GA), researchers are currently looking at a number of unconventional sonographic metrics. Transcerebellar diameter (TCD), fetal kidney length (KL), placental grading, and amniotic fluid volume are the metrics which are included in the list of parameters ^(9).

During the second and third trimesters, the fetal kidney can be easily spotted and measured. At this point in the pregnancy, other measuring tools including hip circumference, biparietal diameter, femur length, and abdominal circumference are no longer useful for estimating the gesta-tional age (GA). Although fetal kidney length (FKL) is a good proxy for gesta-tional age (GA), it has not been extensively studied as a means of predicting GA ⁽¹⁰⁾.

Quick and steady growth characterizes the transcerebellar diameter (TCD), which shows a robust correlation with gestational age (GA) starting in the second trimester. The reliability of TCD as an ultrasound approach for determining GA is established by the end of the second trimester ⁽¹¹⁾.

The current research aims to see how well KL and TCD measure GA in healthy pregnancies that are 19–39 weeks along. We then compared the results from this method to those from the BPD, HC, AC, and FL to see how accurate it was totaly.

Patients and Methods

This is a prospective observational study that was conducted at the antenatal and fetomaternal clinics at Minia Maternity University Hospital, Minia, Egypt in the period from fist of March 2023 up to the end of September 2023. The study was approved by the regional ethics committee at Minia University (IRB No 716:4:2023). An informed written consent was obtained from all participants before enrolling in the current study.

(A) Patients:

A total of seventy-seven pregnant women with a single, simple, normal pregnancy (between 19 and 39 weeks) were included in the study. These women were either certain about their last menstrual cycle or had confirmed their gestational age with a first-trimester ultrasound, using crown-rump length measurement, they were randomly selected from the attendants of the above-mentioned hospital during the study period were asked to be enrolled in the current study.

Women with uncertain knowledge of their most recent menstrual period and significant congenital fetal abnormalities, twins or multiple pregnancies, intrauterine fetal death, antepartum hemorrhage, those with medical disorders like hypertension and diabetes mellitus, and women who refused to participate in this study were also excluded.

All patients were subjected to:

1. History taking:

• Thoroughly collected patient history, specifically focusing on the menstrual history and the date of the last menstrual period (LMP) to confirm the gestational age (GA).
• The expected delivery date (EDD) was calculated using Naegle's formula: EDD = LMP + 7 days + 9 months.

2. Measurement technique:

Patients who met the required inclusion criteria underwent ultrasounds. Every case got regular sonographic examination. The average gestational age was calculated using Headlock's technique, which relies on fetal biometric measurements such as abdominal circumference (AC), head circumference (HC), femur length (FL), and biparietal diameter (BPD). The measurements were collected and documented.The MFKL (Maternal Fetal Kick Count) and TCD (Transcranial Doppler) were also assessed by a skilled obstetrician.

Measurement of kidney length:

The fetus was subjected to transverse imaging modalities until the kidneys became apparent in close proximity to the stomach. Afterwards, the probe was turned by 90° to clearly define the longitudinal axis of the kidneys. Markers were placed on the image of the renal capsule to measure the FKL ⁽¹²⁾.

The regression equation GA = 9.87 + 5.91 x MKL was developed to estimate GA based on a given MKL ⁽¹³⁾.

Measurement of TCD

The trans-cerebellar diameter (TCD) was assessed by positioning the transducer

precisely in the axial plane of the head, with emphasis on visualizing the thalamus. Subsequently, the probe was slightly tilted towards the posterior direction to observe both cerebellar hemispheres. This movement allows for visualization of the cerebellum, cistern magna, and cavum septum pellucidum. The cerebellum is bilaterally symmetrical and is located in the posterior cranial fossa, giving the impression of two lobes on either side of the midline. The trans-cerebellar diameter (TCD) is the measurement of the widest diameter of the cerebellum ^(14).

(B) Statistical analysis:

The statistical computations were performed using version 22 of SPSS (Statistical Package for the Social Sciences; SPSS Inc., Chicago, IL, USA). The data were analyzed using statistical measures such as mean ± standard deviation (±SD) or median and range. The comparison was done using a paired sample t-test, and the results were also provided as numbers and percentages. The Pearson correlation test was used to analyze the correlation between different variables. The p-value has been determined to be statistically significant at the 0.05 level.

Results

Baseline data:

The study had 77 female participants, with an average age of 27.13±5.31 years (ranging from 18 to 40 years). The median parity for pregnancies and the number of abortions were 2 and 3, respectively. The range for pregnancies was between 0 and 6 times, while the range for abortions was between 1 and 9 times. Approximately 77.9% of the participants in the study were living in rural areas, and the majority (79.2%) were primarily engaged in household duties. All participants included in the study had normal menstrual cycles and were clinically healthy, with no previous history of other medical conditions.

Regarding to the fetal presentation; 80.5% had cephalic presentation, with a mean gestational age of 30.22±6.00 weeks (range; 18 to 39 weeks), Table 1.

Discussion

The cornerstone of pregnancy manage-ment is an accurate assessment of the gestational period. Preterm or postterm delivery, both of which can be caused by inaccurate gestational age (GA) estim-ation, can result in significant perinatal morbidity and death. To avoid compli-cations for the mother, it is particularly important to precisely determine the gestational age (GA) in high-risk pregna-ncies when termination is being considered ⁽¹⁵⁾.

There might be a few problems with the traditional method of estimating the due date (EDD) using the last menstrual period (LMP). The likelihood of these compli-cations increases in situations where the LMP is unclear, menstrual cycles are irregular, or first trimester hemorrhage has occurred ⁽¹⁶⁾. In the last twenty years, sonography has made tremendous strides in accurately determining gestational age. Several biometric markers, including head circumference (HC), femur length (FL), crown rump length (CRL), abdominal circumference (AC), and biparietal diameter (BPD), are analyzed to estimate the sonographic gestational age. Multiple pregnancies, aberrant amounts of amniotic fluid, insufficient or excessive fetal growth, and a fetus positioned with its buttocks or feet first are some of the conditions that can impact the accuracy of these gestational age measurements ^{(17, 18)}. Additionally, these measurements do not consistently show the gestational age throughout the second and third trimesters due to the non-uniformity of size changes produced by biological variables in the latter stages of pregnancy. This becomes even more important when women are referred for maternal-fetal care later in the pregnancy or when they have questions about their LMP. Developing trustworthy sonographic gestational markers is of the utmost importance in such cases ⁽¹⁹⁾.

No matter what stage of pregnancy you are in, determining the gestational age should be a simple and basic process. To guarantee the best possible pregnancy care, it is crucial to have reliable sonographic fetal biometric data for gestational age dating in a clinical setting. Deciding when to undertake various prenatal tests, gauging the sufficiency of growth, and planning the delivery for the best possible obstetric outcome are all of the utmost importance ⁽¹²⁾.

Babies with intrauterine growth retardation tend to have wider and more irregularly shaped kidneys than those without the condition. Still, there is no correlation between its duration and any preexisting medical issue (Kansaria and Parulekar, 2010). Independent of preexi-sting growth disorders, a study by Ahmadi et al., (2015) found that foetal growth increased at a rate of 1.1mm per gesta-tional week throughout pregnancy.

There were statistically significant positive connections between gestational age and average fetal kidney length in this study of seventy-seven healthy women experien-cing normal pregnancies. The average length of the fetal kidney was positively correlated with various fetal indices, including AC, BPD, HC, and FL.

Consistent with the current research, Peter et al., discovered a strong relationship between the GA estimated from conven-tional biometric data and the GA predicted using FKL: 9). This study's conclusions were in perfect agreement with those of Abonyi et al., who found a statistically significant relationship between FKL and GA ⁽²⁰⁾. Also, Dash et al., verified that there is a direct relationship between the fetal kidney length (FKL) and the gestational age (GA) advancement⁽²¹⁾. Overlooking other biometric parameters, Munthaian et al., found a strong connection (0.926) between the FKL and the prediction of GA ⁽²²⁾. The measurements of BPD, AC, CRL, HC, and FL in pregnant women were found to have a substantial bilateral connection with FKL in a recent prospective research by Dahmarde and Noori ⁽²³⁾. This idea is supported by the results of the present investigation, which also show that the comparison between TCD and FL had the most significant correlation coefficient, whereas the highest correlation coefficient was obtained between FKL and AC. When Dahmarde and Noori compared FKL with FL, they discovered a high correlation coefficient.

The present study is in agreement with that of Shivalingaiash et al., who examined 60 pregnant women between the ages of 24 and 36 weeks to determine the effect of kidney length on gestational age. Thanks to an early dating scan, these women's pregnancies were precisely pinpointed. In the later trimesters of pregnancy in particular, the researchers discovered a robust association (r = 0.85) between the length of the fetal kidneys and the gestational age. Fetuses with intrauterine growth restriction (IUGR) and other biometric data showed this association ⁽¹⁸⁾.

Notably, the capacity to see many fetal organs, particularly the kidneys, using in utero imaging has been substantially improved by developments in sonographic resolution. Fetal kidneys can now be more easily identified with the use of real-time high-resolution sonography. There was a substantial correlation between FKL and GA in the study that used inaccurate and out-of-date ultrasonography equipment, similar to the one by Cohen and Lemann Jr. In addition, the results showed that the gestational age estimated by FKL and other physiological markers were quite consistent with one another (24). This finding provides more evidence that FKL is useful for assessing the GA.

The results of the present study were consistent with those of Akram et al., and Meenakshi et al., which found no significant differences in kidney size between the right and left sides of the body ^{(25, 26)}. 

As a standard against which to compare deviations in other measurements, the transcerebellar diameter is a useful tool for gestational age (GA) estimation ⁽²⁷⁾. The subject's growth accelerates significantly in the second trimester and continues in a steady linear pattern that is directly related to the gestational age ⁽²⁸⁾. The present study found a strong and statistically significant correlation between GA and transcranial Doppler (r = 0.966, p value <0.001) in normal, uncomplicated pregnancies. Relationships between TCD and BPD (r = 0.905, p < 0.001), HC (r = 0.879, p < 0.001), FL (r = 0.948, p < 0.001), and AC (r = 0.937, p < 0.001) were substantial and statistically significant. Results were similar in a study by Bansal et al., that included 650 cases with GA ranging from 14 to 40 weeks. Researchers discovered a correlation between the gestational age of a fetus and the TCD (Transcranial Doppler) measurement. A correlation coefficient (r) of 0.9723 and a p-value less than 0.001 ⁽²⁹⁾ demonstrated a highly significant and substantial connection between gestational age and TCD.

Prssad and Likhitha conducted their own investigation, which corroborated the results of the current probe. Measurements of intrauterine growth retardation (IUGR) and transcranial Doppler (TCD) in the third trimester were found to be significantly correlated in this study (30). In their third trimester study, Naseem et al., looked at 327 pregnant patients. The research found the gestational age by comparing the results of transcranial Doppler (TCD) and femur length (FL) tests. The findings demonstrated that TCD is an improved technique for third-trimester gestational age determination ⁽³¹⁾. The accuracy of Transcranial Doppler (TCD) in estimating the gestational age (GA) of third-trimester pregnant women was the subject of an Egyptian study by Akl et al., At this point in the pregnancy, the researchers found that TCD is a valid way to measure GA ⁽³²⁾.

This study's results are in agreement with those of Reddy et al., who compared Fetal TCD to other well-established methods for estimating GA from the fifteenth to the forty-first week of pregnancy and assessed its accuracy in predicting GA. Using transcranial Doppler (TCD), they proved that it is a reliable indication of gestational age during the second and third trimesters. Reason being, at the time of the last menstrual period (LMP), there is a substantial correlation between TCD levels and gestational age. Additionally, as shown by Fattah et al.,⁽³³⁾, the transcere-bellar diameter is a more reliable marker of gestational age in the third trimester when compared to other fetal measurements.

Additionally, in healthy pregnancies, Singh et al., (2021) found a strong association (r = 0.975, p value <0.001) between GA and transcranial Doppler (TCD) readings. Additionally, there was a meaningful association between TCD and both BPD (r = 0.950, p < 0.001) and HC (r = 0.966, p < 0.001) ⁽¹²⁾. This leads us to believe that standard measurements of the cerebellum taken during pregnancy can accurately determine the gestational age (GA), regardless of the shape of the baby's head ⁽¹²⁾.  In addition, there was a strong and substantial positive association (r=0.854, p<0.001) between FKL and TCD. This result is also in line with that of Singh et al., who found a strong correlation between the two approaches ⁽¹²⁾.

The results of this experiment showed that the FKL and TCD were significantly related to the GA that was allocated. In addition, the dimensions of the femur and knee, as well as the diameter of the tibial condyle, were positively correlated with that of the patient's Borderline Personality Disorder (BPD), head circumference, abdominal circumference, and lumbar region. Accordingly, when coupled with other biometric indications, FKL and TCD may prove to be valuable predictors, particularly in the second and third trimesters.

In addition, this is very helpful when measuring the infant's head circumference or biparietal diameter becomes challen-ging because the baby is engaged in head movement during pregnancy or because the abdomen circumference is modest because of intrauterine growth restriction (IUGR). In this case, you can use FKL and TCD independently to predict GA. The current research supports the idea that foetal kidney length (FKL) and transchordal diameter (TCD) can be used as reliable sonographic parameters to determine the fetus's gestational age, particularly in the second and third trimesters when other measure-ment indices are not as reliable.

A small sample size, a single center, and the unusual use of transcranial Doppler (TCD) and fetal kidney length measurements in fetal biometry are major limitations of this study.