Maternal emergencies after 20 weeks of pregnancy and in the peripartum period

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Core Mechanism: Medical and traumatic emergencies in the second half of pregnancy (≥20 weeks) are complicated by massive maternal physiologic adaptations, including a hyperdynamic cardiovascular state, dilutional anemia, and a baseline respiratory alkalosis.
• The Mechanical Breakdown (Caval Compression): By 18 to 20 weeks, the gravid uterus physically compresses the inferior vena cava (IVC) when the patient is supine. This mechanical obstruction drastically restricts venous return, potentially decreasing cardiac output by up to 30% and precipitating profound hypotension.
• Placental Abruption vs. Previa: In abruption, the inelastic placenta violently shears away from the elastic uterine wall during deformation (trauma) or hypertensive stress, leading to retroplacental hemorrhage and fetal hypoxia. Placenta previa occurs when the placenta implants abnormally low, partially or fully covering the internal cervical os, risking massive hemorrhage if the cervix dilates or is mechanically disrupted.
• Eclampsia: A state of severe endothelial dysfunction and vasospasm, leading to end-organ ischemia and acute-onset seizures. The risk window spans from 20 weeks of gestation all the way to 8 weeks postpartum.
• Amniotic Fluid Embolism (AFE): A rare but catastrophic maternal inflammatory response to fetal tissue entering the maternal circulation, triggering sudden right ventricular failure, hypoxia, and disseminated intravascular coagulation (DIC).

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization & Positioning: Secure the ABCs and immediately initiate left-lateral uterine displacement (tilting the patient 30 degrees to the left or manually displacing the uterus) to relieve IVC compression.
• Targeted Resuscitation:
• Access: Establish two large-bore IVs above the diaphragm (e.g., antecubital or jugular veins), as lower extremity IVs are ineffective due to IVC compression and potential pelvic venous injury.
• Fluids: Increase standard crystalloid resuscitation volume by 50% to account for the physiologically expanded maternal plasma volume.
• Acute Hypertension & Eclampsia:
• If BP is $\ge$ 160/110 mm Hg, initiate emergent therapy with Labetalol 20 mg IV or Hydralazine 5 mg IV.
• For eclamptic seizures, administer Magnesium Sulfate 4 to 6 g IV load, followed by an infusion of 2 g/hr.
• Resuscitative Hysterotomy (Perimortem C-Section): In maternal cardiac arrest with a fundus at or above the umbilicus (>20 weeks), initiate an emergent vertical midline incision. The procedure must be initiated rapidly with the goal of fetal delivery within 5 minutes of the loss of maternal pulse, which drastically improves both maternal venous return and survival.
• Postpartum Hemorrhage (PPH): Administer uterotonics (Oxytocin, Methergine, Hemabate) and perform aggressive fundal massage. Consider Tranexamic Acid and massive transfusion protocols.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• "Can't-Miss" Mimics & Etiologies:
• Aortic Dissection: Must be considered in any pregnant patient presenting with severe, unexplained chest, back, or neck pain.
• Pulmonary Embolism: Pregnancy represents a severely hypercoagulable state; risk is increased 5 to 6 times, peaking in the 6 weeks postpartum.
• Amniotic Fluid Embolism: Suspect in sudden cardiovascular collapse with DIC during labor or immediately postpartum.
• Head Injury: May closely mimic eclampsia with altered mental status and seizures, and vice versa.
• Prioritized Diagnostic Workup:
• Fetal Cardiotocographic (CTG) Monitoring: Essential. For trauma patients, a minimum of 4 to 6 hours of continuous monitoring is strictly required to rule out fetal distress and occult placental abruption.
• Maternal Labs: Complete blood count (CBC), comprehensive metabolic panel, coagulation profile (PT/PTT, Fibrinogen, FDPs), and a Type & Crossmatch.
• Fetal Maternal Hemorrhage Test: Obtain a Kleihauer-Betke test or flow cytometry on all pregnant trauma patients.
• Transabdominal Ultrasound: Mandatory to assess placental location prior to any digital pelvic examination if $\ge$ 20 weeks.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• The E-FAST & Fetal POCUS:
• Assess Morison's pouch and the splenorenal recess for free intraperitoneal fluid indicating occult maternal hemorrhage.
• Evaluate the fetus for cardiac activity (normal is 120-160 bpm) and measure the femur length (a length >4 cm suggests a gestational age $\ge$ 20 weeks and potential viability).
• The Physical Exam (Fundal Height): Visually and physically assess the uterine fundus. A fundus palpable at or above the umbilicus correlates with a gestational age of $\ge$ 20 weeks, marking the threshold for viability and the necessity of perimortem cesarean section.
• Chest Tube Modification: If placing a thoracostomy tube for trauma, visually adjust your anatomical landmarks and place the tube 1 to 2 intercostal spaces higher (cephalad) than usual due to the diaphragmatic elevation caused by the gravid uterus.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• The Viability Threshold: Fetal viability is generally defined as 22 to 24 weeks of gestation or an estimated weight of 500 grams.
• Trauma Monitoring Guidelines: Most placental abruptions are detected within 6 hours. However, electronic fetal monitoring must be extended to 24 hours if the patient exhibits >6 uterine contractions per hour in any single hour, or has significant abdominal tenderness.
• The "4 Ts" of Postpartum Hemorrhage: Risk-stratify PPH by systematically assessing for Tone (uterine atony, 75-90% of cases), Trauma (lacerations), Tissue (retained placenta), and Thrombin (coagulopathy/DIC).

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• Deadly Cognitive Trap (The Digital Exam): Performing a blind digital pelvic or speculum exam on a patient with 3rd-trimester vaginal bleeding. Critical Action: You must strictly defer the pelvic exam until a transabdominal ultrasound definitively rules out placenta previa to prevent massive, fatal iatrogenic hemorrhage.
• Deadly Cognitive Trap (Reassuring PaCO2): Interpreting a "normal" PaCO2 (e.g., 40 mm Hg) as reassuring in a pregnant trauma patient. Correction: Normal pregnancy induces a baseline respiratory alkalosis (PaCO2 ~30 mm Hg). A PaCO2 of 40 mm Hg actually represents relative hypoventilation and is an early sign of impending respiratory failure.
• Deadly Cognitive Trap (Fetal Prioritization): Focusing resuscitation efforts on the distressed fetus while the mother is in shock. Critical Action: Fetal survival is entirely dependent on maternal survival. The best way to save the fetus is to aggressively resuscitate the mother.
• Critical Action (Rh Status): Ensure all Rh-negative pregnant trauma patients or patients with vaginal bleeding receive Rh immune globulin (RhoGAM) within 72 hours.

7. MCQ MASTERCLASS (Written Exam Tips)

• The Best Trauma Indicator: A board question will ask for the best indicator of fetal outcome following blunt maternal trauma. The options will include maternal vital signs, FAST exam, and abdominal tenderness. Answer: Continuous cardiotocographic monitoring for at least 4 hours is the only reliable predictor of fetal outcome.
• The Seizure Distractor: A 35-week pregnant patient presents with new-onset seizures and a BP of 165/95. The distractor options will push you to use lorazepam or phenytoin. Answer: The definitive first-line therapy for eclamptic seizures is Magnesium Sulfate.
• The Painful vs. Painless Bleeding Rule: "Painless, bright red" third-trimester bleeding strongly points to Placenta Previa. "Painful, dark" vaginal bleeding with a rigid uterus strongly points to Placental Abruption.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Initial Assessment Hook: "Given the patient is visibly pregnant with a fundus above the umbilicus, my immediate priorities are securing her ABCs, placing her in the left lateral decubitus position to relieve caval compression, and obtaining two large-bore IVs strictly above the diaphragm."
• The Diagnostic Command: "For this trauma patient, I will utilize the 'CODE' mnemonic to quickly gather her obstetric history. I am ordering a Kleihauer-Betke test, a comprehensive coagulation panel, and I will consult obstetrics immediately to initiate continuous fetal cardiotocographic monitoring for a minimum of 4 hours to rule out placental abruption."
• The Arrest Pivot: "The patient has lost pulses. Because her fundus is above the umbilicus, I will immediately initiate CPR with continuous manual left uterine displacement. I am calling for the scalpel to perform a resuscitative hysterotomy with a vertical midline incision, with the strict goal of delivering the fetus within 5 minutes of arrest to optimize maternal venous return."