Reproductive · Obstetrics
The facts most likely to be tested
Preterm labor is defined as regular uterine contractions occurring before 37 weeks gestation accompanied by cervical change or cervical dilation of at least 3 cm.
Fetal fibronectin (fFN) testing is indicated for patients with symptoms of preterm labor between 24 and 34 weeks to predict the risk of delivery within the next week.
Betamethasone or dexamethasone is the mandatory antenatal corticosteroid regimen administered to promote fetal lung maturity and reduce risks of respiratory distress syndrome and intraventricular hemorrhage.
Magnesium sulfate is indicated for fetal neuroprotection in patients at risk of imminent delivery before 32 weeks gestation.
Tocolytics such as nifedipine or indomethacin are used for short-term (48-hour) delay of delivery to allow for the administration of corticosteroids.
Indomethacin is contraindicated after 32 weeks gestation due to the risk of premature closure of the ductus arteriosus and oligohydramnios.
Group B Streptococcus (GBS) prophylaxis with intravenous penicillin is required for all patients in preterm labor unless GBS status is known to be negative.
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A 26-year-old G1P0 woman at 30 weeks gestation presents to the labor and delivery unit with regular, painful uterine contractions. On physical examination, the cervix is 3 cm dilated and 50% effaced. The patient is afebrile and the fetus is in a vertex presentation with a reactive non-stress test. The patient has no history of rupture of membranes.
What is the most appropriate next step in management to improve neonatal outcomes?
Administration of betamethasone and magnesium sulfate
The patient meets the criteria for preterm labor; therefore, she requires corticosteroids for fetal lung maturity and magnesium sulfate for neuroprotection, as she is less than 32 weeks gestation.
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Etiology / Epidemiology
Defined as regular uterine contractions with cervical change before 37 weeks gestation. Prior preterm birth is the strongest risk factor.
Clinical Manifestations
Regular, painful contractions with cervical effacement or dilation ≥ 3 cm. Often presents with bloody show.
Diagnosis
Gold standard is fetal fibronectin (fFN) testing and transvaginal ultrasound for cervical length < 20 mm.
Treatment
Administer betamethasone for lung maturity and magnesium sulfate for neuroprotection if < 32 weeks. Use nifedipine for tocolysis.
Prognosis
Major risk is respiratory distress syndrome (RDS). Survival rates improve significantly after 28 weeks.
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Epidemiology & Etiology
Preterm labor accounts for the majority of neonatal morbidity. Key risk factors include multiple gestations, uterine anomalies, and short interpregnancy intervals. Infection, specifically bacterial vaginosis, is a frequent precipitating trigger.
Pertinent Anatomy
The cervix undergoes ripening and shortening prior to labor. Transvaginal ultrasound is the only reliable method to visualize the internal os and measure the cervical length accurately.
Pathophysiology
The process involves premature activation of the maternal-fetal HPA axis and inflammatory cytokine release. Prostaglandins induce myometrial contractions and cervical remodeling. This cascade is often accelerated by decidual hemorrhage or intrauterine infection.
Clinical Manifestations
Patients present with persistent, rhythmic abdominal pain or pelvic pressure. Cervical dilation ≥ 3 cm or cervical length < 20 mm confirms the diagnosis. Chorioamnionitis is a red flag, presenting with maternal fever, tachycardia, and foul-smelling amniotic fluid.
Diagnosis
The fetal fibronectin (fFN) test is a high-negative predictive value tool for patients between 24-34 weeks. A cervical length < 20 mm on transvaginal ultrasound is diagnostic of preterm labor. Always rule out preterm premature rupture of membranes (PPROM) using nitrazine paper and ferning.
Treatment
Tocolysis with nifedipine is first-line to delay delivery for 48 hours. Magnesium sulfate is indicated for fetal neuroprotection if < 32 weeks. Betamethasone must be administered to accelerate fetal lung maturity. Indomethacin is contraindicated after 32 weeks due to risk of premature closure of the ductus arteriosus.
Prognosis
The primary concern is respiratory distress syndrome (RDS) and intraventricular hemorrhage. Neonatal outcomes are inversely proportional to gestational age at birth. Close monitoring for necrotizing enterocolitis is required in the NICU.
Differential Diagnosis
Braxton-Hicks contractions: irregular and non-progressive
PPROM: confirmed by fluid pooling and positive nitrazine test
Abruptio placentae: presents with painful vaginal bleeding and rigid uterus
Urinary tract infection: common trigger for uterine irritability
Appendicitis: localized RLQ pain with rebound tenderness