CT pelvimetry measures the size and shape of the bony pelvis. Although it can produce anatomical measurements, routine pelvimetry should not be used to decide whether a pregnant patient should have vaginal or caesarean birth because pelvic measurements do not reliably predict cephalopelvic disproportion or labour outcome.
If CT pelvimetry is proposed during pregnancy, a senior obstetric and radiology team should identify the unusual, specific question it is expected to answer, explain how the result would change care, consider non-ionising alternatives, and use an optimised low-dose protocol.
Common Indications for CT Pelvimetry
Routine use for suspected cephalopelvic disproportion, previous difficult labour, breech presentation, or planning birth after caesarean is not supported for deciding mode of birth. Rare specialist uses may include selected assessment after major pelvic trauma or deformity when the measurement is expected to change management. Ask the obstetrician to explain the exact indication.
What does a CT Pelvimetry scanner looks like?
The CT scanner is shaped like a wide, circular ring. You lie on a narrow table that gently moves through the center while images of your pelvis are captured.
What happens during a CT Pelvimetry procedure?
- You will lie on your back with legs straight.
- The Radiographer may position you carefully to capture all necessary measurements.
- A quick series of images of your pelvis is taken, it usually lasts less than a minute.
- Specialized software is used to calculate key pelvic dimensions (inlet, outlet, diagonal conjugate, interspinous distance, etc.).
Do I need to prepare for CT Pelvimetry?
No special preparation is usually required.
- You can eat and drink normally before the scan.
- Wear comfortable clothing but you may be asked to change into a hospital gown.
- Remove metallic objects around the pelvic area, such as belts, jewelry, or clothing with zippers or snaps.
Will contrast dye be used?
No, CT Pelvimetry is performed without contrast dye because only the bones of the pelvis are being measured.
How long does CT Pelvimetry take?
The scan itself is very quick, typically less than 5 minutes. Including preparation, you should expect to spend about 10–15 minutes in the CT department.
Is CT Pelvimetry safe during pregnancy?
CT pelvimetry directly exposes the pelvis and fetus to ionising radiation. Dose can vary substantially with technique, so it should not be described as automatically low risk. It should only proceed for a justified specialist indication after alternatives and dose optimisation have been considered.
Does the scan hurt?
No, CT Pelvimetry is painless. You only need to lie still for a short time.
What information does CT Pelvimetry provide?
It provides:
- Accurate measurement of the size and shape of the pelvic bones
- An estimate of the space available for childbirth
- Provides anatomical measurements, but these should not be used alone to predict successful vaginal birth or determine caesarean birth.
Questions to ask your team
- Why is CT pelvimetry being requested, given that routine pelvimetry should not determine mode of birth?
- What specific specialist decision will the measurements change?
- What fetal dose-reduction protocol and non-radiation alternatives were considered?
Sources and further reading
- NICE: Caesarean birth recommendations
- RadiologyInfo: CT safety during pregnancy
- FDA: Computed tomography benefits and risks
Conclusion
CT pelvimetry can provide bony measurements, but it is not a routine or reliable test for choosing vaginal versus caesarean birth. During pregnancy it requires a clearly documented specialist indication, consideration of alternatives, and an optimised radiation protocol.