Accurate assessment of the gestational age is very important for the clinician to impart a good antenatal care as it is very critical in planning the mode of delivery and also in the management of high risk cases and their associated complications [1]. 

Based on certain specific fetal biometric parameters we can determine the age of gestation and fetal growth can also be assessed. The accuracy of gestational age by measuring fetal biometric parameters is maximum in first trimester and accuracy reduces as the fetal age advances from second to third trimester [2].

Transcerebellar diameter is emerging as a promising indicator for assessment of the Gestational age. Because of less variation and less deformation of cerebellum by extrinsic factors transcerebellar diameter is a better predictor of Gestation age than conventional biometric parameters [3,4].

It is also observed that the reliability of almost all the parameters greatly diminishes as gestational age advances [5-8]. In third trimester, the reliability of any single ultrasound parameter is poor. The accuracy of BPD between 12 and 26weeks is +/-10-11days and near term it is +/-3weeks whereas transcerebellar diameter is considered to be more effective as the size of cerebellum is less affected by deviation in fetal growth restriction or growth acceleration. The predicted gestational age by TCD between 22-28 weeks is within 0-2 days whereas between 29-36 weeks it is within 05 days and at 37 week 4 is 09 days of actual gestation. TCD nomogram predicts gestational age with accuracy of 94% in the third trimester [4]. 

So the purpose of our study was to evaluate the Correlation and estimate the Variability between Transcerebellar Diameter and Gestation age in Normal pregnancies.

Aims and Objectives

• To evaluate the Correlation between GA (by LMP) Versus TCD in all normal pregnancies

• To estimate the Variability between Gestation age in weeks according to LMP and the measured TCD in normal patients

• To derive the Quadratic Equation showing relationship of Gestational age with TCD

• To derive the nomogram for estimating the gestational age of the fetus from the measured transverse cerebellar diameter

This study was conducted on 100 antenatal women of gestational age 15-40 weeks with normal pregnancies cases attending the antenatal clinic and admitted in the department of Obstetrics and gynaecology and sent to Department of Radiology KNSH M&C and IGMC Shimla for Antenatal USG Scan:

• Study Design: Prospective Cross-sectional study 

• Study duration: One year 

• Study Place: Department of Radiodiagnosis, Indira Gandhi Medical College, Shimla

Inclusion Criteria

Normal singleton pregnancies of 15 to 40 weeks gestation with known last menstrual period.

Exclusion Criteria

Clinically and radiologically suspected IUGR pregnancies, Congenital Malformations and Multiple pregnancies. 

Machine Specifications

GE LOGIQ P6. The transducer used was 2-5 MHz convex array transducer. Method of Examination: The patient was made to lie in supine position after applying the coupling agent. 

Methodology for Measurement TCD Parameters

In every patient TCD was measured. 

Transcerebellar Diameter

The cerebellar view was obtained by rotating the transducer in the axial plane centred on the thalamus to show the cerebellar hemispheres. This view shows cerebellum, the cistern magna and the cavum septum pellucidi. The cerebellum characteristically appears as two lobules on either side of the midline in the posterior cranial fossa. The widest diameter of the cerebellum is measured. From the above measured parameters gestational age and effective fetal weight was computed by the ultrasound machine based on Hadlock tables by using regression equations from combination of measurements (computation software package). Measured TCD was recorded in millimetres. 

Duration of pregnancy in weeks was recorded as menstrual weeks and days and TCD was recorded in one decimal point. 

Statistical Analysis

Data was entered into MS excel spread sheet, cleaned and transferred to EPI INFO Version 7.2 software. The qualitative variables were presented as percentages, frequencies and proportions. The quantitative variables were presented as mean and standard deviation. Correlation coefficients were then used to compare TCD with Gestational age in normal pregnancies. P values <0.05 was considered significant Data measured in normal pregnancy patients was then utilized to establish nomograms by taking the 5th, 50th and 95th Percentile values.

Ethical Committee Clearance

The research procedure was in accordance with the approved ethical standards of Indira Gandhi Medical College and Hospital, Shimla, Ethics Committee. 

In this study 100 were normal pregnancies were studied. Age distribution of normal pregnancies was 18 to 32 years with Mean age of 24.8±3.25 years. Maximum number of patients (54%) was between 21-25 years followed by 26-30 years (32%). Youngest patient was 18 years old and the eldest was 32 years. Maximum number of patients (44%) was between 30-36 weeks of gestation and least number of patients (5%) were between 12-18 weeks (Table 1).

Table 1: Age and Gestational Age Distribution of the Patients in Normal Pregnancies

It was noted that minimum variability was seen during 12-18 weeks i.e. ±0.34weeks and maximum variability in estimation of gestational age by transcerebellar diameter was seen between 24-30 weeks i.e. ±1.38 weeks (Table 2).

Table 2: Variability Estimates between Gestation Age in Weeks According to LMP and the Measured TCD in Normal Patients

It was observed that during second trimester TCD had the highest correlation with gestational age i.e. 0.987 .It is also noted that TCD has relatively lesser correlation with gestational age in third trimester i.e. 0.788. Overall it was noted that TCD had a strong correlation with gestational age throughout the pregnancy which was statistically significant (Table 3 and Figure 1).

Figure 1: Scattered Plot of TCD Vs GA (by LMP)

Table 3: Correlation between GA (by LMP) Versus TCD in all Normal Pregnancies 

Statistical Analysis: Karl Pearson’s correlation. Correlation is significant at the 0.05 level

A quadratic equation was derived where gestational age can be calculated by taking into account TCD (Table 4).

Table 4: Quadratic Equation Showing Relationship of Gestational Age with TCD

By using the values of all the measured biometric parameters, nomogram was derived at 5^th, 50^th and 95^th percentile for the corresponding gestational age, since we did not include any patient at 15^th 16^th 26^th and 30^th week of gestation in our study so the nomogram for these gestations could not be calculated (Table 5).

Table 5: Normogram Showing Mean TCD Measurements at 5^th, 50^th and 95^th Percentile for the Corresponding Gestational Age

The commonest problem that an obstetrician faces is the accurate assessment of fetal maturity to decide whether the pregnancy should be taken to full term or should be terminated. It is of utmost importance to know the gestational age of the fetus especially in the cases of intrauterine growthrestriction [9].

In our study it was observed that there was maximum variability (least accuracy) in transcerebellar diameter for prediction of gestational age between 24-30 weeks.

In a similar study done by Dashottar et al. [10], it was observed that correlation between TCD and gestational age was strong at 16-20 and >20-24 weeks. It was moderate at >24-28 weeks and mild at >32-35 and >36-40 weeks. The results of our study were not in concurrence with the above study as the variability between TCD and gestational age was highest between 24-30 weeks (±1.34) followed by 36-42 weeks (±0.78).It was also noted that since the patients studied between 24-30weeks of gestation were significantly less in number than the patients studied between 30-36weeks, this could be one reason for the maximum variability observed in it.

We noted that there was a good correlation between TCD and gestational age. Similar study was done by Reece et al. [11] who prospectively studied ultrasonography of 371 normal pregnant women, with gestational ages ranging from 13 weeks to 40 weeks. They found curvilinear relationships between the transverse diameter of the cerebellum and the gestational age (R2 = 0.948; p = 0.001). A nomogram of cerebellar measurements estimating gestational age was generated. Chavez et al. [12] concluded that throughout pregnancy normative cerebellar measurements allows for estimation of gestational age that is independent of the shape of fetal head. The result of our study was in concurrence with the above observations and there was good correlation between TCD and gestational age (R2 = 0.974, p-value<0.001).

Orji [13] reported that TCD of the fetus ranges from 11.9 mm (at 13 weeks) to 59.3 mm at 41 weeks with a mean value of 34.2±14.1 mm. There was significant correlation between TCD and menstrual gestational age (r = 0.984, p = 0.000) TCD has a predictive accuracy of 96.9% with high standard error of ±10 days. Our study was in concurrence with the above study and showed a significant correlation between gestation age and TCD (R = 0.974; p<0.001).

In this study TCD nomogram was established from sonographically measured data which can be used for estimating the gestational age of fetus. Smith et al. [14] demonstrated that the fetal cerebellum can be visualized with ultrasound throughout the second trimester. Nomograms of transcerebellar diameter measurements against gestational age showed good correlation and narrow confidence limits.

It was noticed that early visualization of cerebellum by ultrasonography occurred as early as 14 weeks [14]. It was also seen that TCD had a strongest correlation with gestational age in second and early third trimester as there was good visualization of cerebellum in each case and measurements were easier to perform in second and early third trimester in comparison to late third trimester in the study done by Smith et al. [14] Similar results were observed in our study, it was seen that amongst all the parameters TCD has the strongest correlation with gestational age during second trimester (R2 = 0.98) and it significantly reduced in the third trimester (R2 = 0.78). This could be due to poor visualization of cerebellum in the third trimester hampering its accurate measurement and also it was observed that the growth rate of cerebellum increases in third trimester. A study done by Malik et al. [15] observed that the fetal cerebellum grows in linear pattern in second trimester and the curve flattens in the third trimester.

The potential of transcerebellar diameter in predicting the gestational age in normal pregnancies has thus been stated .Its accuracy being more in second than in third trimester has also been demonstrated.

Limitations of the Study

In our study early dating of pregnancy by ultrasound was not done in all the patients since most of the patients were from rural background where ultrasound facilities are not available. The number of patients studied between POG 24-30 weeks was less (n = 8) as compared to the other study groups. Our study did not include any patient at 15th 16th 26th and 30th week of gestation in our study so the nomograms for these gestations could not be calculated.

It was observed that in normal pregnancies TCD is an effective and accurate parameter to predict the gestational age in second trimester. The correlation of TCD with gestation age decreases as the pregnancy advances and was least in the third trimester since the growth rate of cerebellum is more in the third trimester. It is thus established that TCD is an independent reliable marker for estimation of gestational age in normal pregnancies. The nomograms and quadratic equation derived from the measured TCD data at 5^th, 50th and 95th percentile can be used to calculate the gestational age of the fetus.

1. Kramer, M.S. et al. "US Black vs White disparities in foetal growth: Physiological or pathological?" Int. J. Epidemiol., vol. 35, 2006, pp. 1187–1195.

2. Cughey, A.B. et al. "First vs second trimester ultrasound: The effect on pregnancy dating and perinatal outcomes." Am. J. Obstet. Gynecol, vol. 198, no. 6, 2008, pp. 703–705.

3. Araujo, E.J. et al. "Correlation of the fetal cerebellar volume with other fetal growth indices by three dimensional ultrasound." J. Matern. Fetal Neonatal Med., vol. 20, no. 8, 2007, pp. 581–587.

4. Chavez, M.R. et al. "Fetal transcerebellar diameter measurement with particular emphasis in the third trimester: A reliable predictor of gestational age." Am. J. Obstet. Gynecol, vol. 191, no. 3, 2004, pp. 979–984.

5. Hadlock, F.P. et al. "Fetal abdominal circumference as a predictor of menstrual age." Am. J. Roentgenol, vol. 139, no. 2, Aug. 1982, pp. 367–370.

6. Hadlock, F.P. et al. "Fetal biparietal diameter: A critical re-evaluation of the relation to menstrual age by means of real time ultrasound." Ultrasound Med., vol. 1, no. 3, Apr. 1982, pp. 97–104.

7. Hadlock, F.P. et al. "Fetal head circumference: relation to menstrual age." Am. J. Roentgenol., vol. 138, no. 4, Apr. 1982, pp. 649–653.

8. Deter, RL. et al. "Fetal head and abdominal circumferences: II a critical re-evaluation of the relationship to menstrual age." J. Clin. Ultrasound, vol. 10, no. 8, Oct. 1982, pp. 365–372.

9. Scott, K.E. and R. Usher. "Fetal malnutrition: Its incidence, causes and effects." Am. J. Obstet. Gynaecol., vol. 94, no. 7, Apr. 1966, pp. 951–963.

10. Dashottar, S. et al. "Transcerebellar diameter: An effective tool in predicting gestational age in normal and IUGR pregnancy." Int. J. Reprod. Contracept Obstet Gynecol, vol. 7, no. 10, 2018, pp. 4190–4196.

11. Reece, E.A. et al. "Cerebellar measurements with ultrasonography in the evaluation of fetal growth and development." Am. J. Obstet. Gynecol., vol. 156, no. 5, May 1987, pp. 1065–1069.

12. Chavez, M.R. et al. "Fetal transcerebellar diameter measurement for prediction of gestational age at the extremes of fetal growth." J. Ultrasound. Med., vol. 26, no. 9, Sep. 2007, pp. 1167–1171.

13. Orji, M.O. and A.A. Adeyekun. "Ultrasound estimation of foetal gestational age by transcerebellar diameter in healthy pregnant Nigerian women." West Afr. J. Med., vol. 33, no. 1, 2014, pp. 61–67.

14. Smith, P.A. et al. "Prenatal measurement of the fetal cerebellum and cisterna cerebellomedullaris by ultrasound." Prenat. Diagn., vol. 6, no. 2, Mar. 1986, pp. 133–141.

15. Malik, G. et al. "Determination of gestational age by transverse cerebellar diameter in third trimester of pregnancy." J. Coll. Physicians Surg. Pak., vol. 16, no. 4, 2006, pp. 249–252.