A 27-year-old woman, gravida 2, para 1, at 37 weeks' gestation is admitted to the hospital in active labor. She has received routine prenatal care, but she has not been tested for group B streptococcal (GBS) colonization. Pregnancy and delivery of her first child were complicated by an infection with GBS that resulted in sepsis in the newborn. Current medications include folic acid and a multivitamin. Vital signs are within normal limits. The abdomen is nontender and contractions are felt every 4 minutes. There is clear amniotic fluid pooling in the vagina. The fetus is in a cephalic presentation. The fetal heart rate is 140/min. Which of the following is the most appropriate next step in management?

Administer intrapartum intravenous penicillin

Obtain vaginal-rectal swab for nucleic acid amplification testing

Obtain vaginal-rectal swab for GBS culture

Obtain vaginal-rectal swab for GBS culture and nucleic acid amplification testing

A 29-year-old G1P0 presents to her obstetrician for her first prenatal care visit at 12 weeks gestation by last menstrual period. She states that her breasts are very tender and swollen, and her exercise endurance has declined. She otherwise feels well. She is concerned about preterm birth, as she heard that certain cervical procedures increase the risk. The patient has a gynecologic history of loop electrosurgical excision procedure (LEEP) for cervical dysplasia several years ago and has had negative Pap smears since then. She also has mild intermittent asthma that is well controlled with occasional use of her albuterol inhaler. At this visit, this patient’s temperature is 98.6°F (37.0°C), pulse is 69/min, blood pressure is 119/61 mmHg, and respirations are 13/min. Cardiopulmonary exam is unremarkable, and the uterine fundus is just palpable at the pelvic brim. Pelvic exam reveals normal female external genitalia, a closed and slightly soft cervix, a 12-week-size uterus, and no adnexal masses. Which of the following is the best method for evaluating for possible cervical incompetence in this patient?

Transvaginal ultrasound at 18 weeks gestation

Transabdominal ultrasound in the first trimester

Transvaginal ultrasound in the first trimester

Serial transvaginal ultrasounds starting at 16 weeks gestation

Transabdominal ultrasound at 18 weeks gestation

A 31-year-old woman, gravida 2, para 1, at 32 weeks' gestation comes to the emergency department for sudden leakage of clear vaginal fluid. Her pregnancy has been uncomplicated. Her first child was born at term by vaginal delivery. She has no history of serious illness. She does not drink alcohol or smoke cigarettes. Current medications include vitamin supplements. Her temperature is 37.2°C (98.9°F), pulse is 70/min, respirations are 18/min, and blood pressure is 128/82 mm Hg. Speculum examination demonstrates clear fluid in the cervical canal. The fetal heart rate is reactive at 160/min with no decelerations. Tocometry shows uterine contractions. Nitrazine testing is positive. She is started on indomethacin. Which of the following is the most appropriate next step in management?

Administer betamethasone and ampicillin

Administer betamethasone, ampicillin, and proceed with cesarean section

Administer betamethasone, ampicillin, and proceed with induction of labor

Administer ampicillin and perform amnioinfusion

Administer ampicillin and test amniotic fluid for fetal lung maturity

A P2G1 diabetic woman is at risk of delivering at 29 weeks gestation. Her obstetrician counsels her that there is a risk the baby could have significant pulmonary distress after it is born. However, she states she will give the mother corticosteroids, which will help prevent this from occurring. Additionally, the obstetrician states she will perform a test on the amniotic fluid which will indicate the likelihood of the infant being affected by this syndrome. Which of the following ratios would be most predictive of the infant having pulmonary distress?

lecithin:phosphatidylserine < 1.5

lecithin:phosphatidylserine > 3.0

A P1G0 diabetic woman is at risk of delivering at 30 weeks gestation. Her obstetrician counsels her that there is a risk the baby could have significant pulmonary distress after it is born. However, she states she will administer a drug to the mother to help prevent this from occurring. By what action will this drug prevent respiratory distress in the premature infant?

Increasing the secretory product of type II alveolar cells

Promoting increased surface tension of alveoli

Suppressing the neonatal immune system

Preventing infection of immature lungs

Reducing the secretory product of type II alveolar cells

A 26-year-old gravida 1 at 36 weeks gestation is brought to the emergency department by her husband complaining of contractions lasting up to 2 minutes. The contractions are mostly in the front of her abdomen and do not radiate. The frequency and intensity of contractions have not changed since the onset. The patient worries that she is in labor. The blood pressure is 125/80 mm Hg, the heart rate is 96/min, the respiratory rate is 15/min, and the temperature 36.8°C (98.2℉). The physical examination is unremarkable. The estimated fetal weight is 3200 g (6.6 lb). The fetal heart rate is 146/min. The cervix is not dilated. The vertex is at the -4 station. Which of the following would be proper short-term management of this woman?

Reassurance, hydration, and ambulation

Admit to the Obstetrics Department for observation

Admit to the Obstetrics Department in preparation for labor induction

Perform an ultrasound examination

A 30-year-old woman, gravida 2, para 1, at 38 weeks' gestation comes to the hospital for regular, painful contractions that have been increasing in frequency. Her pregnancy has been complicated by gestational diabetes treated with insulin. Pelvic examination shows the cervix is 50% effaced and 4 cm dilated; the vertex is at -1 station. Ultrasonography shows no abnormalities. A tocometer and Doppler fetal heart monitor are placed on the patient's abdomen. The fetal heart rate monitoring strip shows a baseline heart rate of 145/min with a variability of ≥ 15/min. Within a 20-minute recording, there are 7 uterine contractions, 4 accelerations, and 3 decelerations that have a nadir occurring within half a minute. The decelerations occur at differing intervals relative to the contractions. Which of the following is the most appropriate next step in the management of this patient?

Placement of fetal scalp electrode

A 33-year-old woman, gravida 2, para 1, at 26 weeks' gestation comes to the emergency department because of frequent contractions. The contractions are 40 seconds each, occurring every 2 minutes, and increasing in intensity. Her first child was delivered by lower segment transverse cesarean section because of a nonreassuring fetal heart rate. Her current medications include folic acid and a multivitamin. Her temperature is 36.9°C (98.4°F), heart rate is 88/min, and blood pressure is 126/76 mm Hg. Contractions are felt on the abdomen. There is clear fluid in the vulva and the introitus. The cervix is dilated to 5 cm, 70% effaced, and station of the head is -2. A fetal ultrasound shows polyhydramnios, a median cleft lip, and fused thalami. The corpus callosum, 3rd ventricle, and lateral ventricles are absent. The spine shows no abnormalities and there is a four chamber heart. Which of the following is the most appropriate next step in management?

Perform dilation and evacuation

A 30-year-old woman, gravida 2, para 1, at 31 weeks' gestation is admitted to the hospital because her water broke one hour ago. Pregnancy has been complicated by iron deficiency anemia and hypothyroidism treated with iron supplements and L-thyroxine, respectively. The patient followed-up with her gynecologist on a regular basis throughout the pregnancy. Pregnancy and delivery of her first child were uncomplicated. Pulse is 90/min, respirations are 17/min, and blood pressure is 130/80 mm Hg. The abdomen is nontender. She has had 8 contractions within the last hour. Pelvic examination shows cervical dilation of 3 cm. The fetal heart rate is 140/min with no decelerations. In addition to administration of dexamethasone and terbutaline, which of the following is the most appropriate next step in the management of this patient?

Administration of magnesium sulfate

Administer prophylactic azithromycin

Administration of anti-RhD immunoglobulin

Preterm labor management for USMLE Step 1: High-Yield OB/GYN Lessons

Diagnosis - Too Soon, Too Fast

Gestational Age: <37 weeks
Uterine Contractions: Regular, painful uterine activity.
- ≥4 in 20 minutes OR ≥8 in 60 minutes.
Cervical Change: Documented cervical effacement ≥80% or dilation ≥3 cm.

Key Predictors for Equivocal Cases:

Transvaginal Ultrasound (TVUS):
- Gold standard for cervical length (CL).
- A short cervix (<25 mm before 24 wks) is a strong predictor.
Fetal Fibronectin (fFN):
- Glycoprotein "glue"; its presence in cervicovaginal secretions indicates disruption.

⭐ The primary value of fFN testing is its high Negative Predictive Value (NPV). A negative result is >99% reliable in ruling out delivery within the next 7-14 days.

Ultrasound: Cervical Length Measurement

Tocolysis - Hit The Brakes

Goal: Delay delivery for 48 hours to allow antenatal corticosteroids (e.g., Betamethasone) to enhance fetal lung maturity.
📌 Mnemonic: It's Not My Time
- Indomethacin
- Nifedipine
- Magnesium Sulfate
- Terbutaline

Tocolytics Mechanism of Action in Uterine Muscle Cell

Contraindications:
- Indomethacin (NSAID): Avoid after >32 weeks (premature ductus arteriosus closure).
- Nifedipine (CCB): Avoid with maternal hypotension.
- Terbutaline (β-agonist): Avoid in maternal cardiac disease, poorly controlled diabetes.
- Magnesium Sulfate: Avoid in myasthenia gravis. Check for toxicity (↓ reflexes, respiratory depression).

⭐ High-Yield: Magnesium Sulfate given before <32 weeks also provides fetal neuroprotection, reducing the risk of cerebral palsy.

Antenatal Corticosteroids - Baby's Breath Boost

Goal: Accelerate fetal lung maturity to ↓ risk of Neonatal Respiratory Distress Syndrome (NRDS).
Mechanism: Stimulates surfactant production from Type II pneumocytes.
Primary Window: Given between 24 0/7 and 34 0/7 weeks for patients at risk of preterm delivery within 7 days.
Regimens:
- Betamethasone: 12 mg IM q24h x 2 doses.
- Dexamethasone: 6 mg IM q12h x 4 doses.
Key Benefits: ↓ NRDS, intraventricular hemorrhage (IVH), and necrotizing enterocolitis (NEC).

⭐ A single rescue course can be considered for patients < 34 0/7 weeks if the prior course was >14 days ago and they are at risk of delivering within 7 days.

Antenatal Corticosteroids for Preterm Birth Outcomes

Neuroprotection & GBS Prophylaxis - Guard the Brain & Gut

Magnesium Sulfate ($MgSO_4$) for Neuroprotection:
- Indication: Viable gestation to < 32 weeks with likely imminent delivery.
- Goal: ↓ risk & severity of cerebral palsy by stabilizing fetal brain circulation.
- Dose: 4-6 g IV load, then 1-2 g/hr maintenance infusion.
Group B Strep (GBS) Prophylaxis:
- Goal: Prevent early-onset neonatal GBS sepsis.
- Indication: Unknown GBS status + delivery < 37 wks, ROM > 18 hrs, or intrapartum fever; or known GBS positive.
- Regimen: Penicillin G 5 million units IV load, then 2.5-3 million units q4h until delivery.

⭐ High-Yield: Magnesium sulfate for neuroprotection is a separate indication from its use as a tocolytic. It is given specifically at < 32 weeks to reduce cerebral palsy risk, even if tocolysis is not attempted.

High‑Yield Points - ⚡ Biggest Takeaways

Preterm labor is defined as regular uterine contractions causing cervical change before 37 weeks gestation.

Administer antenatal corticosteroids (e.g., Betamethasone) for patients at < 34 weeks to promote fetal lung maturity.

Tocolytics (Indomethacin, Nifedipine) are used to delay delivery for 48 hours, allowing corticosteroids to work.

Provide Magnesium Sulfate for fetal neuroprotection if gestation is < 32 weeks.

GBS prophylaxis with Penicillin is a critical intervention.

Tocolysis is contraindicated in cases like chorioamnionitis or non-reassuring fetal status.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play