1.1 Prerequisites for X-Rays

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  Minimum X-ray dose (<5 rad; i.e., 0.05 Gy) to be used.

  
  
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  Fetal shielding is required.

  
  
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  First trimester X-rays must be avoided. Hence, every woman should provide the date of her last menstrual period to avoid inadvertent X-rays in early pregnancy.

  
  
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  USS/MRI scan must be considered as an alternative investigation in comorbid conditions.

1.2 Indications

With the advent of high-resolution USS and MRI, there is almost no role of an X-ray in fetal and maternal imaging.

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  Intrauterine fetal death (IUFD): is easily diagnosed by the absence of cardiac activity by USS. However, certain bony signs are suggestive of IUFD and would be visualised on an X-ray.

  
  
  
  
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     ◦ Spalding sign: irregular overlapping of the cranial bones due to liquefaction of brain matter and softening of ligaments. Appears seven days after death.

     
     
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     ◦ Hyperflexion of the spine.

     
     
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     ◦ Crowding of ribs.

     
     
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     ◦ Roberts sign: appearance of gas shadow in the heart chambers and great vessels. Appears within 12 hours of intrauterine fetal death.

  
  
  
  
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  Ossification centres of lower end of the femur appears at 32 weeks and that of the upper end of the tibia appears at 36 weeks and this may give an indication of fetal maturity.

  
  
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  Secondary abdominal pregnancy: presence of an empty endometrial cavity and the presence of a fetus in the abdomen confirms an abdominal pregnancy. Again, with USS being widely available, even in developing countries, an abdominal radiograph would rarely be used. Where further imaging is indicated, an MRI scan is more useful as it can also delineate the placental position and attachments.

1.3 Maternal Indications

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  X-Ray pelvimetry is occasionally performed in cases of pelvic deformity or pelvic fractures.

2.1 Modes of Ultrasound Imaging in Obstetrics and Gynaecology

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  Transabdominal sonography.

  
  
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  Transvaginal sonography.

  
  
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  Transrectal and transperineal sonography.

  
  
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  Doppler interrogation of arteries and veins to ascertain blood flow.

  
  
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  Saline infusion sonography to visualise the endometrial cavity.

  
  
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  Endoscopic ultrasound probes are being developed to ascertain the degree of tissue invasion and vascularity of dense adhesions.

2.2 Standard Ultrasound Images

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  B-mode: a two-dimensional ultrasound image display composed of bright dots representing the ultrasound echoes. Using brightness mode display, two-dimensional images are obtained, in greyscale.

  
  
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  M-mode: to study moving organs; for example, fetal heart rate.

  
  
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  3D imaging refers to reconstruction of a three-dimensional picture after capturing an ultrasound image.

  
  
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  4D is the viewing of three-dimensional images in motion.

  
  
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  Colour Doppler is used to map and study blood flow in arteries and veins. If the blood is flowing towards the transducer, the vessels will appear red (artery) and if the blood is flowing away from the transducer, the vessels will appear blue (vein).

  
  
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  Pulse wave Doppler study reveals that systolic and diastolic blood flow patterns in arteries are consistent and can be studied to calculate the systolic:diastolic ratio, pulsatility index and resistance index of a vessel.

  
  
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  Pulse Doppler index shows the capillary perfusion in a structure.

2.3 Transabdominal Sonography

Transabdominal sonography is the preferred mode of imaging in the second and third trimesters of pregnancy. It utilises a 3–5 MHz curvilinear transducer. A distended urinary bladder provides a good reference point for pelvic structures and acts as an acoustic window to improve transmission of ultrasound waves. It also pushes the uterus upwards for clear imaging and displaces the small intestine from the field of view. However, it does not allow accurate assessment of cervical length.

Fetal anomaly scans, growth scans, echocardiography, placental localisation and Doppler assessments are performed transabdominally. All invasive procedures during pregnancy (such as fetal reduction, amniocentesis, cordocentesis and drainage of obstructive lesions like hydronephrosis and ventriculomegaly) are performed under abdominal ultrasound guidance.