Lesson 11

Lesson 11

Prematurity

• Defined as delivery before 37 weeks gestation (less than 259 days).

• Leading cause of perinatal morbidity and mortality.

• Higher risk for newborns < 1,500 g.

• Increased incidence with multiple gestations and premature rupture of membranes.

• Complications: respiratory distress syndrome, intraventricular hemorrhage, NEC, hypoglycemia, hypocalcemia, hyperbilirubinemia.

Tocolysis

• Tocolytic agents delay labor (24-48 hours) to allow corticosteroids to enhance fetal lung maturity.

• Common agents:
  • Beta-agonists
  • Magnesium sulfate
  • Calcium channel blockers
  • Nitric oxide donors

• Antibiotic prophylaxis for chorioamnionitis given in conjunction.

• Tocolytics/corticosteroids seldom given after 33 weeks gestation.

Beta-2 Agonists

• Function: Increase intracellular cAMP -> relax uterus via protein kinase activation.

• Side effects:
  • Hyperglycemia (risk of post-delivery hypoglycemia in newborns)
  • Hypokalemia
  • Can cross the placenta increasing fetal heart rate.

Magnesium Sulfate

• Acts as a calcium antagonist, relaxing smooth muscle.

• Used for seizure prophylaxis in preeclampsia.

• Monitoring needed for renal insufficiency.

Magnesium Toxicity

• Assess hypermagnesemia via reflex testing:
  • Presence -> low serious side effect risk
  • Diminished reflexes -> sign of toxicity

• Additional side effects of hypermagnesemia: skeletal muscle weakness, pulmonary edema, reduced responsiveness to drugs.

• Treatment: supportive care, diuretics, IV calcium gluconate.

Magnesium Levels

• Normal: 1.8-2.5 mg/dL

• Hypomagnesemia: <1.2 mg/dL (symptoms include tetany, seizures, dysrhythmias)

• Hypermagnesemia: >2.5 mg/dL - severe effects at > 12 mg/dL (cardiac arrest, coma).

Calcium Channel Blockers

• Reduce uterine contractions by blocking Ca+2 influx.

• First-line drug: oral nifedipine.

Nitric Oxide Donors

• Function: Vasodilator, relaxes uterine muscle via cGMP.

• Rarely used due to risk of hypotension.