Management of Preterm Labor

Hydration

Always hydrate first in preterm labor. It often stops contractions. Dehydration causes antidiuretic hormone (ADH) secretion, and ADH mimics oxytocin (both made in posterior pituitary).

Tocolytic Therapy

Tocolysis is used if < 34 weeks.

Tocolytic Agents

■ IV magnesium sulfate—suppresses uterine contractions

■ Oral calcium channel blocker (nifedipine)

■ Beta mimetics (ritodrine, terbutaline)—stimulate beta-2 receptors on myometrial cells ^ increase cyclic adenosine monophosphate (cAMP) ^ decrease intracellular Ca ^ decrease contractions

Side effects: Pulmonary edema, tachycardia, headaches

■ Prostaglandin inhibitors (indomethacin)

Side effects: Premature constriction of ductus arteriosus, pulmonary HTN, and interventricular hemorrhage

Contraindications to Tocolysis

■ Severe Bleeding from any cause

■ Severe Abruptio placentae

■ Fetal Death/life-incompatible anomaly

■ Chorioamnionitis

■ Severe pregnancy-induced Hypertension

■ Unstable maternal hemodynamics

Action

■ Acts as Ca2+ antagonist and reduces actin-myosin interaction (at 7 mg/100 mL)

Side Effects

■ Decreases deep tendon reflexes (at 8 to 10 mg/100 mL)

■ Respiratory/cardiac depression (at > 12 mg/100 mL)

■ Flushing, warmth, headaches, nystagmus, dizziness, dry mouth, hypocal-cemia

Mnemonic for contraindications to tocolysis: BAD CHU

■ Severe Bleeding from any cause

■ Severe Abruptio placentae

■ Fetal Death/life-incompatible anomaly

■ Chorioamnionitis

■ Severe pregnancy-induced Hypertension

■ Unstable maternal hemodynamics

About Magnesium Sulfate

■ Magnesium sulfate antagonizes Ca and decreases intracellular Ca, thus decreasing contractions. It is 70 to 90% effective in achieving 2 to 3 days of tocolysis.

Side effects: Depressed reflexes, pulmonary edema, fatigue. Toxicity is treated with calcium gluconate.

Mg Level

Corticosteroids

Side Effect

Uterine contractions decreased Depressed deep tendon reflexes Respiratory/cardiac depression

■ Given to patients in preterm labor from 24 to 35 weeks unless they have chorioamnionitis

■ Reduce fetal mortality: Accelerate fetal lung maturity (decreases respiratory distress syndrome [RDS]), reduce intraventricular hemorrhage, and reduce necrotizing enterocolitis

Lecithin-Sphingomyelin Ratio

An amniocentesis may be performed to assess fetal lungs for risk of RDS. Fetal lungs are mature if:

■ Phosphatidylglycerol is present in amniotic fluid or

■ Lecithin-sphingomyelin ratio is > 2

PREMATURE RUPTURE OF MEMBRANES

PROM is the most common diagnosis associated with preterm delivery.

Premature rupture denotes spontaneous rupture of fetal membranes before the onset of labor. This can occur at term (PROM) or preterm (PPROM).

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