Is TCD a reliable marker for fetal dating in obstetrics ultrasound?

-

Fetal biometry plays a crucial role in estimating gestational age (GA) and monitoring fetal growth. Traditionally, parameters like biparietal diameter (BPD), head circumference (HC), femur length (FL), and abdominal circumference (AC) have been widely used. However, transcerebellar diameter (TCD) is emerging as a more reliable marker, especially in cases of abnormal growth patterns.

But is TCD truly superior for fetal dating? Let’s explore the science behind it.

Why TCD is a Reliable Marker for Gestational Age

TCD measures the width of the cerebellum in the posterior fossa of the fetal brain. Studies have shown that cerebellar growth follows a linear pattern throughout pregnancy, making it a consistent and reliable marker for dating pregnancies.

Key Advantages of TCD for Gestational Age Estimation

1. Less Affected by Fetal Growth Abnormalities

Traditional measurements like AC and FL can be significantly affected by intrauterine growth restriction (IUGR), skeletal dysplasias, or macrosomia.

TCD remains relatively unaffected by these conditions, making it a better alternative in compromised pregnancies.

2. Resistant to External Factors

Head molding from uterine compression can distort BPD and HC measurements, especially in cases of oligohydramnios or breech presentations.

TCD is less affected by head compression, preserving its accuracy.

3. Reliable in the Third Trimester

BPD becomes less reliable after 28 weeks due to fetal head molding, but TCD remains a consistent indicator of GA even in later gestation.

4. Strong Correlation with Gestational Age

Several studies have confirmed that TCD correlates strongly with gestational age, making it useful for both early and late pregnancy assessments.

How TCD Compares to Traditional Biometric Measurements

Scientific Studies Supporting TCD Reliability

1. Chavez et al. (2004) – TCD in Growth-Restricted Fetuses

Published in the American Journal of Obstetrics and Gynecology, this study found that TCD remains accurate for dating fetuses with IUGR, while BPD and AC significantly underestimated gestational age.

2. Goldstein et al. (1987) – Correlation of TCD with Gestational Age

A landmark study published in Obstetrics & Gynecology demonstrated a strong correlation between TCD and GA throughout pregnancy, confirming its reliability.

3. Malik et al. (2021) – TCD as a Late-Pregnancy Dating Tool

Research in The Journal of Maternal-Fetal & Neonatal Medicine emphasized that TCD is particularly useful when standard parameters become unreliable in the third trimester.

Is TCD More Reliable for Fetal Dating?

The answer depends on the clinical scenario.

In normal pregnancies, BPD, HC, FL, and AC are still effective tools for gestational age estimation.

In cases of IUGR, skeletal abnormalities, or head molding, TCD proves to be more reliable than traditional measurements.

For late pregnancy dating, TCD outperforms BPD, making it an excellent choice for estimating gestational age in the third trimester.

Final Verdict: TCD should be included as a routine biometric measurement, especially in cases where other parameters are unreliable.

How to Integrate Transcerebellar Diameter (TCD) into Fetal Ultrasound Practice

Integrating Transcerebellar Diameter (TCD) into routine fetal ultrasound practice enhances accuracy in gestational age (GA) estimation, particularly in cases where traditional biometric measurements are unreliable. Below is a step-by-step guide to successfully incorporating TCD into your practice.

1. Understand When to Use TCD

While TCD can be used in all fetal assessments, it is most useful in the following cases:

Uncertain gestational age (e.g., late booking with unknown last menstrual period)

Intrauterine growth restriction (IUGR) (where BPD and AC may underestimate GA)

Head molding due to oligohydramnios or breech presentation

Skeletal dysplasias or abnormal femur length

Third-trimester dating, when BPD becomes less reliable

2. Optimize Your Ultrasound Protocol

A. Equipment Settings

Use a mid-range frequency probe (3–5 MHz) for optimal penetration and resolution.

Adjust depth and gain settings to clearly visualize the posterior fossa.

B. Scanning Technique

1. Obtain the Transverse Axial Plane

Position the probe in the transcerebellar plane, which is slightly lower than the standard BPD plane.

Identify key landmarks:

Cerebellum (butterfly-shaped structure)

Cisterna magna (fluid-filled space behind the cerebellum)

Cavum septi pellucidi (CSP) (anterior landmark)

2. Measure the TCD

Place calipers outer to outer across the widest part of the cerebellum.

Ensure the midline structures (thalamus, falx cerebri) are symmetrical for accuracy.

3. Record and Compare with Standard Charts

Use established TCD reference charts for gestational age estimation.

Cross-check with BPD, HC, FL, and AC for a comprehensive assessment.

3. Train Staff and Educate Patients

Sonographer Training: Conduct hands-on workshops and use case studies to familiarize sonographers with TCD measurement techniques.

Physician Awareness: Educate obstetricians on the benefits of TCD, especially in complex cases.

Patient Education: Explain to patients why additional measurements like TCD may be necessary for more accurate dating.

4. Incorporate TCD into Reporting and Diagnosis

A. Update Ultrasound Report Templates

Include a section for TCD measurement in standard fetal biometry reports.

If gestational age estimation differs significantly from other parameters, mention it in the conclusion.

B. Use TCD to Improve Diagnostic Accuracy

If there’s a discrepancy between TCD and other biometric parameters, consider possible conditions:

Small TCD: Suggests cerebellar hypoplasia or genetic syndromes.

Large TCD: May indicate cerebellar overgrowth syndromes.

Combine TCD with Doppler studies to assess fetal well-being in IUGR cases.

By integrating TCD into your routine fetal ultrasound practice, you improve gestational age accuracy and enhance diagnostic confidence in challenging cases. Ready to start? Update your scanning protocols today and see the difference!

Comments

  1. AnonymousFebruary 27, 2025 at 3:18 AM

    TCD is reliable for gestational age (GA) estimation throughout pregnancy, from as early as 14 weeks up to full term (40 weeks). However, its reliability is most notable in the second and third trimesters due to its linear growth pattern and resistance to factors like head molding and growth abnormalities.

    Studies suggest that:

    First trimester: TCD is not commonly used for GA estimation.

    Second trimester (14–28 weeks): Highly accurate for GA estimation.

    Third trimester (28–40 weeks): More reliable than BPD and HC, especially in cases of IUGR or altered head shape.


    Because the cerebellum continues growing at a predictable rate even in cases of growth restriction, TCD remains a valuable biometric tool even in late pregnancy.

    ReplyDelete

Post a Comment

Popular posts from this blog

Hepatic Pregnancy: A Rare Form of Ectopic Pregnancy

-
Image
A few days ago, a colleague shared a video of a real-time pregnancy developing in the liver, and I was in complete disbelief. This is an extremely rare form of ectopic pregnancy, with an estimated incidence of 1 in 8,000 births. While abdominal pregnancies are already uncommon, hepatic pregnancies—where the embryo implants in the liver—are even more exceptional. Recent Case in Namibia A recently reported case in Namibia has reignited discussions in the medical community about this rare phenomenon. The video evidence highlights the complexity of hepatic pregnancies and the significant challenges in their management. Understanding Hepatic Pregnancy Hepatic pregnancy falls under the broader category of abdominal pregnancies, which account for approximately 1.4% of all ectopic pregnancies. Most abdominal pregnancies implant in the pelvis, but in extremely rare cases, implantation occurs in the upper abdomen, particularly in the liver. Case Study from the Literature A documented case publi...
Read more

Choris prosopos fetalis: Faceless birth defect

-
Image
"Choris prosopos fetalis" or absent fetal face is a congenital birth defect that can be classified in the arthrogryposis multiplex congentia . This is the absence of facial bone due to failure of ossification centres, and eventual bone formation. The inability for bone formation results in the malformation of other facial organs like the mouth, nose and eyes. Choris prosopos fetalis is a very rare form of facial deformity with almost zero survival rate this is very similar to but not  Frontonasal Dysplasia , also known as Median Cleft Face Syndrome, is a condition in which the nose has a flat, wide appearance, and the eyes may be wide-set. There is a groove of varying degrees, which runs down the middle of the face across the nose. In some cases the tip of the nose is missing. A gap with extra folds of skin covering it may appear on the front of the head. Craniofacial defects are caused by the abnormal growth or development of the head and/or facial bones wh...
Read more

Medical news: live shots of an ovulating ovary

-
Image
Alot is known on the physiology of female reproductive system . These knowledge has been the fulcrum on which modern day reproductive medicine is practiced, the success of medical practice is hinged on the culmination of all piece of know. But not all that has been taught will ever be seen, some processes occurs when man isn't looking. In a very rare sight during surgery, the first time for many practitioners, there was an ovulation caught on camera. The pic below is a live still image of an ongoing ovulation during surgery. Exciting sight for many In the collage picture the process starts from top right and ends in bottom right of the image.
Read more