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Chapter 37: Peripartum Imaging

Asma Assiri; Abdalmajed Eisa

ULTRASOUND IN THE MODERN ERA

Advances in medical technologies have allowed us to think out of the box and augment our practical skills with direct visualization using ultrasound, including portable machines. Some use handheld ultrasound probes that can be wirelessly connected to any device with a screen, such as smartphones. Although ultrasound cannot replace clinical assessment, it can improve the quality of care and answer questions that no clinical exam can (e.g., location of the placenta).

The chapter focuses on imaging techniques directly applicable to patients presenting to the labor and delivery unit. This can be collectively referred to as peripartum ultrasound (Table 37-1). Regardless of the type of scan, fetal viability should be assessed every time.

TABLE 37-1:ROLES FOR PERIPARTUM ULTRASOUND
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TABLE 37-1: ROLES FOR PERIPARTUM ULTRASOUND
Antepartum Ultrasound Intrapartum Ultrasound Postpartum Ultrasound Other Uses

  • Fetal viability

  • Fetal number

  • Antepartum bleeding (placenta previa, vasa previa, or placenta abruption)

  • Biometry

  • Amniotic fluid volume

  • Preoperative mapping

  • Biophysical profile

  • First stage:

    1. Presentation

    2. Placenta location

    3. Breech assessment (type, neck flexion, and EFW)

  • Second stage:

    1. Head position

    2. Head station

    3. Head direction

    4. Midline angle

    5. Subpubic angle

    6. Second twin assessment

  • Third stage of labor complications (retained products of conception and PPH)

  • Ultrasound-guided operative procedures (D&C, MROP, and placement of a Bakri balloon)

  • Invasive procedures

    1. Amnioreduction

    2. Drainage of abnormal fetal fluid collections

  • Bladder residual volume

  • Local and regional anesthesia

  • Nuchal cord

  • Fetal Dopplers

  • Placental maturity

The following ultrasound assessments should be within the skill set of most obstetricians practicing in labor and delivery. A key practical point is to always ensure that the probe orientation matches the screen orientation. This ensures “left” and “cranial” are always depicted correctly on the screen. Gently moving your finger on one corner of the probe and observing the screen will confirm this before you start scanning.

Because ultrasound is transmitted poorly through air, the face of the transducer must be coupled to the patient’s skin by a fluid medium, such as gel, so that the sound waves may penetrate the skin surface–air interface. Higher ultrasound frequencies are used on vaginal probes, giving finer, more detailed resolution of structures. However, the higher frequency beam can only penetrate a short distance, and therefore the field depth is limited. Lower frequency probes are used transabdominally, giving greater depth and penetration.

In order to reflect real obstetric practice, the images used in this chapter were either obtained using a basic, older-model ultrasound machine (as typically found in most labor and delivery units) or a newer handheld, portable unit.

ANTEPARTUM ULTRASOUND

Fetal Viability

Using real-time ultrasound, fetal cardiac motion can be readily appreciated within the fetal chest. Confirming fetal viability can help avoiding a Cesarean section in some cases of nonviable fetus. By applying color or power Doppler, ...

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