15.1 Antepartum Emergencies, Preeclampsia & Normal Spontaneous Childbirth

15.1 Antepartum Emergencies, Preeclampsia & Normal Spontaneous Childbirth

Maternal Physiological Adaptations to Pregnancy

Pregnancy induces profound, multi-organ anatomical and physiological adaptations designed to support fetal growth and protect the mother from blood loss during delivery. Primary care paramedics under the Canadian Paramedic Competence Framework (CPCF Appendix A #2, #13) must interpret baseline vital signs and trauma presentations through the lens of these gestational adaptations.

Cardiovascular Adaptations

• Intravascular Volume Expansion: Total maternal blood volume increases by 40% to 50% (approximately 1.5 litres above non-pregnant baselines). Maternal plasma volume expands disproportionately (up to 50%) relative to erythrocyte mass (which expands 20% to 30%), producing a state of physiological anemia of pregnancy with a normal term hemoglobin of 105 to 120 g/L and hematocrit of 30% to 34%.
• Resting Hemodynamics: Resting heart rate increases progressively by 10 to 15 beats per minute above baseline by the third trimester. Cardiac output increases by 30% to 50% due to augmented stroke volume and heart rate.
• Systemic Vascular Resistance (SVR): Circulating progesterone stimulates vascular smooth muscle relaxation while the low-resistance uteroplacental vascular bed dilates, causing a marked decrease in SVR. Blood pressure typically falls during the second trimester (diastolic dipping 5 to 10 mmHg) before returning toward normal pre-pregnancy levels near term.
• Compensated Hemorrhage: Because of the expanded circulating blood volume, a pregnant patient can lose 30% to 35% of total blood volume (1200–1500 mL) before exhibiting conventional signs of shock (such as hypotension or marked tachycardia). However, maternal compensatory mechanisms aggressively vasoconstrict the uterine arcuate and radial arteries, shunting blood away from the placenta to preserve maternal central perfusion. Fetal distress and severe hypoxia inevitably precede maternal decompensation.

Respiratory Adaptations

• Diaphragmatic Displacement: As the gravid uterus enlarges, it elevates the diaphragm cephalad by up to 4 cm, accompanied by an increase in the transverse diameter of the thoracic cage. This anatomical displacement decreases the Functional Residual Capacity (FRC) by approximately 20%.
• Ventilation Dynamics: High levels of circulating progesterone act as a direct respiratory stimulant on the medullary center, increasing tidal volume by 30% to 40% with minimal change in respiratory rate. This heightened minute ventilation produces a baseline physiological respiratory alkalosis (normal arterial blood gas in third-trimester pregnancy: PaCO2 28 to 32 mmHg, bicarbonate 18 to 21 mmol/L, pH 7.40 to 7.45).
• Oxygen Consumption: Maternal metabolic oxygen demand increases by 20% to 30%. The combination of elevated oxygen consumption and diminished FRC means that pregnant patients become hypoxemic and desaturate precipitously during hypoventilation, airway obstruction, or rapid sequence management.

Gastrointestinal Adaptations

• Progesterone-mediated smooth muscle relaxation decreases lower esophageal sphincter tone and reduces gastrointestinal motility, delaying gastric emptying. Combined with mechanical cephalad compression of the stomach by the uterus, all pregnant patients in active labor or beyond 20 weeks gestation are considered to have a full stomach and carry a high risk of pulmonary aspiration.

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Supine Hypotensive Syndrome & Aortocaval Compression

When a pregnant patient in the second or third trimester lies flat on her back, the heavy gravid uterus compresses two major retroperitoneal vessels against the lumbar vertebral column:

1. Inferior Vena Cava (IVC) Compression: Occlusion of the IVC curtails venous return (preload) to the right atrium, which can reduce stroke volume and cardiac output by 25% to 30%.
2. Abdominal Aorta Compression: Compression of the descending aorta directly compromises blood flow to the iliac arteries and uterine circulation, reducing uteroplacental perfusion pressure.

Clinical Presentation

Within 3 to 10 minutes of lying supine, the mother may develop supine hypotensive syndrome:

• Maternal pallor, diaphoresis, lightheadedness, dizziness, syncope, nausea, and a profound drop in systolic blood pressure.
• Fetal bradycardia and distress resulting from acute placental hypoperfusion.

Prehospital Corrective Management

• Left Lateral Tilt: Place the patient in a 15° to 30° left lateral tilt by placing a firm wedge, rolled blanket, or specialized positioning device under the patient's right hip and flank.
• Manual Left Uterine Displacement (LUD): If the patient is immobilized on a spinal board or undergoing CPR, a rescuer manually grasps the uterus with one or two hands and pulls/pushes it toward the patient's left side.
• Spinal Motion Restriction / Transport: Pregnant patients should never be packaged, immobilized, or transported completely flat in the supine position.

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Antepartum Bleeding Emergencies: Placenta Previa vs. Placental Abruption

Vaginal bleeding during the third trimester represents a critical obstetrical emergency requiring rapid differentiation between the two most prevalent structural pathologies:

[!CAUTION] Absolute Contraindication to Digital Vaginal Examination: Paramedics must NEVER perform a digital vaginal examination on any pregnant patient presenting with unexplained second- or third-trimester vaginal bleeding. Inserting fingers through the cervix can puncture or shear the low-lying placental disc of placenta previa, provoking sudden, catastrophic maternal exsanguination and fetal demise within minutes. Physical assessment is strictly limited to visual inspection of the perineum.

Prehospital Management of Antepartum Hemorrhage

1. Administer high-flow oxygen via non-rebreather mask (15 L/min) to maintain maternal PaO2 and optimize fetal oxygenation.
2. Position the patient in a left lateral tilt (15°–30°) to prevent aortocaval compression.
3. Establish two large-bore intravenous lines (16G or 14G) en route; infuse warmed isotonic crystalloid (normal saline or lactated Ringer's) in titrated boluses (250–500 mL) to maintain maternal radial pulses and an SBP of 90 to 100 mmHg.
4. Collect and save all expelled blood clots and saturated sanitary pads to allow hospital staff to estimate total blood loss. Never pack dressings or gauze into the vagina.
5. Initiate rapid priority transport with immediate pre-arrival notification to an obstetrical surgical facility.

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Hypertensive Disorders of Pregnancy: Preeclampsia & Eclampsia

Hypertensive disorders complicate up to 10% of all pregnancies and remain a leading cause of maternal and fetal morbidity in Canada.

Clinical Spectrum & Definitions

• Gestational Hypertension: New-onset Systolic Blood Pressure (SBP) ≥140 mmHg or Diastolic Blood Pressure (DBP) ≥90 mmHg occurring after 20 weeks of gestation in a previously normotensive patient, without proteinuria or systemic end-organ signs. Blood pressure returns to normal within 12 weeks postpartum.
• Preeclampsia: Multisystem endothelial disorder developing after 20 weeks gestation characterized by hypertension (SBP ≥140 or DBP ≥90 mmHg on two occasions at least 4 hours apart) accompanied by proteinuria (≥1+ on urine dipstick) OR evidence of maternal end-organ dysfunction:
  • Central Nervous System: Persistent, throbbing frontal or occipital headache unresponsive to analgesics, visual disturbances (scotomata, blurred vision, photophobia, temporary blindness), brisk deep tendon reflexes (hyperreflexia), and patellar clonus.
  • Hepatic: Severe, persistent epigastric or right upper quadrant abdominal pain (resulting from hepatic microvascular ischemia and distension of Glisson's capsule), accompanied by elevated liver enzymes (AST/ALT).
  • Hematologic: Thrombocytopenia (platelets <100 × 10^9/L), microangiopathic hemolytic anemia, or HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets).
  • Renal / Pulmonary: Serum creatinine >97 µmol/L, oliguria, and non-cardiogenic pulmonary edema.
• Eclampsia: The development of new-onset generalized tonic-clonic seizures or unexplained coma in a patient with preeclampsia, occurring during the antepartum, intrapartum, or postpartum period (up to 4–6 weeks post-delivery).

Pathophysiological Cascade

Preeclampsia stems from abnormal trophoblastic invasion of the maternal spiral arteries during early placentation. The failure of spiral arteries to transform into wide, low-resistance channels causes chronic placental hypoperfusion and ischemia. The ischemic placenta releases antiangiogenic factors and inflammatory cytokines into maternal circulation, triggering widespread systemic vascular endothelial dysfunction, microvascular thrombosis, intense arterial vasospasm, and capillary leakage.

Prehospital Management of Preeclampsia and Eclampsia

1. Environment: Minimize sensory stimulation. Transport in a calm, darkened environment with sirens extinguished whenever possible to prevent triggering seizures.
2. Positioning & Oxygen: Position the mother in a left lateral tilt; administer high-flow oxygen if SpO2 <95% or if seizures occur.
3. Seizure Management in Eclampsia:
   • Protect the patient from physical trauma (pad side rails); do NOT force objects into the mouth.
   • Suction the oropharynx gently only after the seizure ceases; maintain lateral positioning.
   • Magnesium Sulfate: The definitive anticonvulsant for eclampsia per the Society of Obstetricians and Gynaecologists of Canada (SOGC). Primary care paramedics should rendezvous with Advanced Life Support (ALS) for administration of a magnesium sulfate IV loading dose of 4 g to 5 g over 15 to 20 minutes, followed by a maintenance infusion (1–2 g/hr). Paramedics must monitor for signs of magnesium toxicity (loss of deep tendon reflexes, respiratory depression <12/min, hypotension, cardiac arrest); calcium gluconate (1 g IV over 10 minutes) serves as the specific reversal agent.
   • If ALS is unavailable or seizures are prolonged (status epilepticus), PCP protocols authorize midazolam (5–10 mg IM or 2–5 mg IV/IN) for immediate seizure termination.

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Stages of Labor & Signs of Imminent Delivery

Normal spontaneous labor progresses through three distinct, sequential physiological stages:

1. Stage 1 (Cervical Dilation & Effacement): Begins with the onset of regular, painful uterine contractions and ends when the cervix is fully dilated to 10 cm and 100% effaced. Subdivided into:
   • Latent Phase: Slow cervical dilation from 0 to 5 cm; contractions irregular or 5 to 15 minutes apart.
   • Active Phase: Rapid cervical dilation from 6 to 10 cm; contractions become regular, intense, lasting 60 to 90 seconds and occurring every 2 to 3 minutes.
2. Stage 2 (Fetal Expulsion / Delivery of Infant): Begins with full cervical dilation (10 cm) and ends with the complete delivery of the newborn. The mother experiences an involuntary, reflex urge to bear down (the Ferguson reflex). In primigravidas (first-time mothers), this stage lasts 1 to 2 hours; in multigravidas, it may proceed precipitously in 15 to 30 minutes.
3. Stage 3 (Placental Expulsion): Begins immediately following delivery of the newborn and concludes with the complete expulsion of the placenta and fetal membranes. This stage typically lasts 5 to 30 minutes.

Clinical Indicators of Imminent Field Delivery

Paramedics must immediately assess whether delivery will occur on scene or if safe transport to an obstetrical center is feasible. The presence of the following signs dictates immediate preparation for on-scene field delivery:

• Contractions occurring less than 2 minutes apart, lasting 60 to 90 seconds, and regular.
• The mother expresses an overwhelming, involuntary urge to push or reports feeling like having an immediate bowel movement (caused by the fetal head compressing the rectum against the sacrum).
• Maternal vocalizations change from rhythmic breathing to involuntary, deep grunting or groaning.
• Physical inspection reveals crowning: the fetal presenting part (occiput) is visible at the vaginal introitus and does not regress between contractions.
• Perineal bulging, flattening of the anus, or gaping of the rectal sphincter.
• History of multiparity with previous rapid or precipitous labors.

[!IMPORTANT] Transport Decision Rule: If the fetal head is crowning or the mother is experiencing an uncontrollable urge to push with frequent contractions, NEVER attempt transport. Place the patient in a safe, controlled environment and prepare the field delivery kit immediately. Delivering an infant unassisted in a moving ambulance compromises safety for both mother and neonate.

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Stepwise Field Delivery Technique

When imminent delivery is recognized, the primary care paramedic executes a systematic, calm delivery protocol:

[Imminent Delivery Recognized]
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[Control Head Descent & Support Perineum]
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[Check for Nuchal Cord Upon Head Delivery]
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[External Rotation (Restitution)]
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[Deliver Anterior Shoulder (Gentle Downward Traction)]
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[Deliver Posterior Shoulder (Gentle Upward Traction)]
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[Deliver Trunk & Rest of Body]
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[Immediate Thermal Care & Airway Clearance If Needed]
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[Delayed Cord Clamping (60s) & Cutting]
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[Deliver Placenta Spontaneously (No Traction)]
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[Initiate Skin-to-Skin & Fundal Massage]

1. Preparation & Positioning

• Create a warm, clean, draft-free environment. Turn off vehicle air conditioning.
• Position the mother in a semi-Fowler position or dorsal lithotomy with hips slightly elevated and a small wedge under the right flank to maintain lateral uterine displacement.
• Open the sterile obstetrical (OB) kit: lay sterile drapes beneath the buttocks and over the abdomen. Prepare the neonatal bulb syringe, umbilical cord clamps, sterile scissors, warm towels, and neonatal resuscitation bag-valve-mask (BVM).

2. Controlling the Fetal Head

• As the head crowns, place the flat palm of one gloved hand gently against the emerging fetal skull. Apply gentle counter-pressure to slow the exit of the head.
• Rationale: Controlling descent prevents explosive delivery. Explosive delivery causes severe maternal perineal tears (third- and fourth-degree lacerations involving the anal sphincter) and can induce rapid fetal intracranial decompression, resulting in subdural or tentorial hemorrhages.
• Concurrently, support the maternal perineal tissues with a sterile towel held by the other hand.
• If the amniotic sac remains intact as the head crowns ("born in the caul"), tear or snip the membranes with gloved fingers away from the infant's face and peel them off the head immediately.

3. Checking for Nuchal Cord

• As soon as the fetal head delivers, it undergoes restitution (external rotation to align with the fetal spine). Immediately slide a gloved index finger along the baby's neck to check if the umbilical cord is wrapped around the neck (nuchal cord).
• If a loose nuchal cord is present, gently slip the loop over the infant's head.
• If the cord is tight or coiled multiple times and cannot be slipped over the head, immediately apply two umbilical clamps side-by-side onto the cord around the neck, cut between the clamps with sterile scissors, and proceed immediately with shoulder delivery.

4. Delivering the Shoulders & Body

• Support the head with both hands placed on the parietal bones. Do NOT pull or twist.
• During the next contraction, guide the head gently downward (toward the maternal rectum) to allow the anterior shoulder to slip beneath the maternal symphysis pubis.
• Once the anterior shoulder is visualized, guide the head gently upward (toward the maternal abdomen) to deliver the posterior shoulder over the perineum.
• The remainder of the infant's torso and lower extremities will deliver rapidly. The infant is extremely slippery; grasp the torso securely around the thorax and pelvis using a dry, warm towel.

5. Airway Management & Suctioning Guidelines

• Routine bulb suctioning of healthy, vigorous newborns is strictly contraindicated.
• Suctioning the mouth and hypopharynx triggers vagal stimulation, resulting in reflex bradycardia, apnea, and laryngeal spasm.
• Suction the mouth first, then the nose ("M before N") using a bulb syringe ONLY IF the airway is visibly obstructed by thick secretions, blood, or meconium, or if the infant requires positive pressure ventilation.

6. Umbilical Cord Clamping and Cutting

• If the newborn is vigorous, delay cord clamping for at least 60 seconds (delayed cord clamping per SOGC guidelines) to facilitate physiological placental transfusion, enhancing neonatal hemoglobin levels and iron stores.
• Apply the first umbilical clamp approximately 10 cm (4 inches) from the infant's abdomen.
• Apply the second umbilical clamp 5 cm (2 inches) distal to the first clamp (approximately 15 cm from the abdomen).
• Cut the cord cleanly between the two clamps using sterile scissors. Inspect the cut ends for active bleeding; apply a third clamp proximal to the first if oozing persists.

7. Placental Delivery

• Allow the placenta to detach and deliver spontaneously (typically within 5 to 20 minutes). Look for signs of placental separation: sudden lengthening of the umbilical cord, a gush of dark blood from the vagina, and the uterus rising and becoming firm and globular.
• NEVER apply traction or pull on the umbilical cord. Pulling on the cord can tear the placenta or cause acute uterine inversion, an immediate life-threatening obstetrical catastrophe causing catastrophic neurogenic shock and massive hemorrhage.
• Place the delivered placenta and membranes into a biohazard bag and transport them to the hospital for physician inspection to ensure no cotyledons were retained.
• Place the dried, warm infant skin-to-skin directly on the mother's chest, cover both with dry warm blankets, and initiate fundal massage.

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Clinical Scenario: Imminent Multiparous Delivery in the Field

Paramedics are dispatched to a private residence for a 31-year-old female (Gravida 3, Para 2) at 39 weeks gestation complaining of severe labor contractions. Upon arrival, the patient is kneeling on the bedroom floor, groaning uncontrollably, and stating, "The baby is coming right now, I need to push!"

1. Primary Assessment & Visual Inspection: Paramedic 1 assesses vital signs (BP 128/78 mmHg, HR 96 bpm, SpO2 98%) while Paramedic 2 visually inspects the perineum with the patient's consent. Contractions are occurring every 90 seconds. Crowning is clearly visible, with 4 cm of the fetal occiput showing at the introitus between contractions. Paramedic 1 immediately cancels the transport decision and announces an on-scene delivery.
2. Setup: Paramedic 2 places a sterile drape beneath the patient's buttocks and preheats two sets of dry bath towels while opening the sterile obstetrical kit. Paramedic 1 positions a rolled towel under the patient's right hip.
3. Controlled Delivery of Head: As the next contraction peaks, the patient bears down involuntarily. Paramedic 1 places a gloved palm over the advancing occiput, applying gentle counter-pressure while supporting the perineum with a sterile pad. The fetal head delivers smoothly without tearing the perineal tissues.
4. Nuchal Check & Shoulder Delivery: Paramedic 1 immediately sweeps a gloved index finger around the infant's neck and palpates a loose loop of umbilical cord. The loop is easily slipped forward over the infant's occiput. External rotation occurs spontaneously. Paramedic 1 gently directs the head downward until the anterior shoulder slips under the pubic symphysis, then guides the head upward to release the posterior shoulder. The rest of the infant delivers smoothly at 14:22.
5. Post-Delivery Care: The infant is vigorous, crying lustily, and has active muscle tone. Paramedic 2 immediately places the newborn directly onto the mother's bare chest, thoroughly dries the infant's head and body with warm towels, and covers mother and infant with a fresh dry blanket. At 60 seconds, Paramedic 1 double-clamps the cord at 10 cm and 15 cm and cuts between them. Ten minutes later, the placenta delivers spontaneously without cord traction and is placed into an OB bag. Paramedic 1 performs gentle fundal massage; the uterus remains firm and bleeding is minimal (<150 mL).

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Exam Pitfalls & High-Yield Obstetrical Pearls

• Performing a Digital Vaginal Exam in Antepartum Bleeding: Never insert fingers into the vagina of a bleeding pregnant patient. It can puncture placenta previa and trigger fatal exsanguination.
• Transporting a Crowning Patient: Never load and drive with a crowning multipara. Deliver on scene in a controlled environment.
• Traction on the Umbilical Cord: Never pull on the cord to expedite placental expulsion. Cord traction causes acute uterine inversion.
• Supine Transport: Never allow a patient in late pregnancy to remain flat on her back. Maintain a 15° to 30° left lateral tilt to prevent aortocaval compression.
• Routine Vigorous Airway Suctioning: Never routinely suction a vigorous, crying infant. Bulb suctioning triggers vagal bradycardia and laryngeal spasm.