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 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

A 28-year-old primigravid woman at 36 weeks' gestation comes to the emergency department because of worsening pelvic pain for 2 hours. Three days ago, she had a burning sensation with urination that resolved spontaneously. She has nausea and has vomited fluid twice on her way to the hospital. She appears ill. Her temperature is 39.7°C (103.5°F), pulse is 125/min, respirations are 33/min, and blood pressure is 130/70 mm Hg. Abdominal examination shows diffuse tenderness. No contractions are felt. Speculum examination shows pooling of nonbloody, malodorous fluid in the vaginal vault. The cervix is not effaced or dilated. Laboratory studies show a hemoglobin concentration of 14 g/dL, a leukocyte count of 16,000/mm3, and a platelet count of 250,000/mm3. Fetal heart rate is 148/min and reactive with no decelerations. Which of the following is the most appropriate next step in management?

Administer intravenous ampicillin and gentamicin and induce labor

Administer oral azithromycin and induce labor

Administer intravenous ampicillin and gentamicin and perform C-section

A 34-year-old gravida 2 para 1 woman at 16 weeks gestation presents for prenatal care. Her prenatal course has been uncomplicated. She takes no medications besides her prenatal vitamin which she takes every day, and she has been compliant with routine prenatal care. She has a 7-year-old daughter who is healthy. The results of her recent quadruple screen are listed below: AFP: Low hCG: Low Estriol: Low Inhibin-A: Normal Which of the following is the most appropriate next step to confirm the diagnosis?

Ultrasound for nuchal translucency

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 29-year-old G2P1 at 35 weeks gestation presents to the obstetric emergency room with vaginal bleeding and severe lower back pain. She reports the acute onset of these symptoms 1 hour ago while she was outside playing with her 4-year-old son. Her prior birthing history is notable for an emergency cesarean section during her first pregnancy. She received appropriate prenatal care during both pregnancies. She has a history of myomectomy for uterine fibroids. Her past medical history is notable for diabetes mellitus. She takes metformin. Her temperature is 99.0°F (37.2°C), blood pressure is 104/68 mmHg, pulse is 120/min, and respirations are 20/min. On physical examination, the patient is in moderate distress. Large blood clots are removed from the vaginal vault. Contractions are occurring every 2 minutes. Delayed decelerations are noted on fetal heart monitoring. Which of the following is the most likely cause of this patient's symptoms?

Premature separation of a normally implanted placenta

Amniotic sac rupture prior to the start of uterine contractions

Placental implantation over internal cervical os

Chorionic villi attaching to the myometrium

Chorionic villi attaching to the decidua basalis

Premature rupture of membranes for USMLE Step 3: High-Yield OB/GYN Lessons

Diagnosis - Water Break Whodunit

Positive Fern Test for PROM

Initial Steps:
- Sterile Speculum Exam: Visualize for pooling of fluid.
- Nitrazine Test: Amniotic fluid is alkaline (pH > 6.5), turning paper blue. ⚠️ False positives: blood, semen, BV.
- Fern Test: Fluid air-dries on a slide, showing a crystallization pattern (arborization). Most specific office test.
If Diagnosis Unclear:
- Ultrasound: Assess for oligohydramnios (AFI < 5 cm).

⭐ The fern test is highly specific for amniotic fluid, as the characteristic arborization pattern is caused by the crystallization of amniotic salts and proteins when dried.

Etiology & Risks - The Weak Link

Infection: The primary driver, weakening membranes.
- Ascending genital tract infections (e.g., bacterial vaginosis)
- UTIs, chorioamnionitis
Uterine Overdistension / Stress:
- Polyhydramnios, multiple gestation
Iatrogenic/Traumatic:
- Amniocentesis, cervical surgery (LEEP, conization)
Intrinsic Membrane Weakness:
- Prior PPROM, smoking, nutritional deficiencies (Vit C, copper)

⭐ A history of PPROM in a prior pregnancy is the single strongest predictor for recurrence.

Complications - Danger Zone Delivery

Umbilical cord prolapse types

Maternal Risks:
- Chorioamnionitis: Most common; intra-amniotic infection.
- Placental abruption: Can cause severe hemorrhage.
- Endometritis & retained placenta post-delivery.
Fetal/Neonatal Risks:
- Umbilical Cord Prolapse: EMERGENCY requiring immediate C-section.
- Pulmonary Hypoplasia: High risk if rupture <24 weeks.
- Prematurity: Major cause of RDS, IVH, NEC.
- Infection: Neonatal sepsis, pneumonia.

⭐ Chorioamnionitis is the most frequent major complication. Suspect with maternal fever, uterine tenderness, maternal or fetal tachycardia, and purulent amniotic fluid.

Management - The Ticking Clock

Management hinges on gestational age and presence of infection or fetal distress.

Expectant Management (<34 wks):
- Corticosteroids (e.g., Betamethasone): For fetal lung maturity.
- Latency Antibiotics (e.g., Ampicillin + Azithromycin): To prolong pregnancy.
- Magnesium Sulfate: If <32 wks for fetal neuroprotection.

⭐ In PPROM, latency antibiotics are given to prolong the interval to delivery and reduce neonatal infectious morbidity, not primarily to treat maternal infection.

High-Yield Points - ⚡ Biggest Takeaways

Rupture of membranes before labor onset is the defining feature.

Diagnose with a sterile speculum exam showing amniotic fluid pooling, a positive nitrazine test (turns blue), and microscopic ferning.

The greatest risks are intra-amniotic infection (chorioamnionitis) and preterm labor.

At term (≥37 weeks), proceed to delivery and induce labor.

For PPROM <34 weeks, manage expectantly with latency antibiotics (e.g., ampicillin, azithromycin) and corticosteroids for fetal lung maturity.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play