A 36-year-old primigravid woman at 26 weeks' gestation comes to the physician complaining of absent fetal movements for the last 2 days. Pregnancy was confirmed by ultrasonography 14 weeks earlier. She has no vaginal bleeding or discharge. She has a history of type 1 diabetes mellitus controlled with insulin. Vital signs are all within the normal limits. Pelvic examination shows a soft, 2-cm long cervix in the midline with a cervical os measuring 3 cm and a uterus consistent in size with 24 weeks' gestation. Transvaginal ultrasonography shows a fetus with no cardiac activity. Which of the following is the most appropriate next step in management?

Plan for oxytocin administration

Perform weekly pelvic ultrasound

A 26-year-old gravida 4 para 1 presents to the emergency department with sudden severe abdominal pain and mild vaginal bleeding. Her last menstrual period was 12 weeks ago. She describes her pain as similar to uterine contractions. She has a history of 2 spontaneous abortions in the first trimester. She is not complaining of dizziness or dyspnea. On physical examination, the temperature is 36.9°C (98.4°F), the blood pressure is 120/85 mm Hg, the pulse is 95/min, and the respiratory rate is 17/min. The pelvic examination reveals mild active bleeding and an open cervical os. There are no clots. Transvaginal ultrasound reveals a fetus with no cardiac activity. She is counseled about the findings and the options are discussed. She requests to attempt medical management with mifepristone before progressing to surgical intervention. Which of the following describes the main mechanism of action for mifepristone?

Increase myometrial sensitivity to contractions and induce decidual breakdown

Interferes with cell growth in rapidly dividing cells

Induce teratogenesis in the fetus

Interferes with placental blood supply to the fetus

A 27-year old primigravid woman at 37 weeks' gestation comes to the emergency department because of frequent contractions for 4 hours. Her pregnancy has been complicated by hyperemesis gravidarum which subsided in the second trimester. The contractions occur every 10–15 minutes and have been increasing in intensity and duration since onset. Her temperature is 37.1°C (98.8°F), pulse is 110/min, and blood pressure is 140/85 mm Hg. Uterine contractions are felt on palpation. Pelvic examination shows clear fluid in the vagina. The cervix is 50% effaced and 3 cm dilated. After 4 hours the cervix is 80% effaced and 6 cm dilated. Pelvic examination is inconclusive for the position of the fetal head. The fetal heart rate is reassuring. Which of the following is the most appropriate next step?

Perform external cephalic version

Perform Mauriceau-Smellie-Veit maneuver

A 24-year-old woman, gravida 1, at 35 weeks gestation is admitted to the hospital with regular contractions and pelvic pressure for the last 5 hours. Her pregnancy has been uncomplicated and she has attended many prenatal appointments and followed the physician's advice about screening for diseases, laboratory testing, diet, and exercise. She has had no history of fluid leakage or bleeding. At the hospital, her temperature is 37.2°C (99.0°F), blood pressure is 108/60 mm Hg, pulse is 88/min, and respirations are 16/min. Cervical examination shows 60% effacement and 5 cm dilation with intact membranes. Cardiotocography shows a contraction amplitude of 220 MVU in 10 minutes. Which of the following is the most appropriate pharmacotherapy at this time?

No pharmacotherapy at this time

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 22-year-old female presents to her PCP after having unprotected sex with her boyfriend 2 days ago. She has been monogamous with her boyfriend but is very concerned about pregnancy. The patient requests emergency contraception to decrease her likelihood of getting pregnant. A blood hCG test returns negative. The PCP prescribes the patient ethinyl estradiol 100 mcg and levonorgestrel 0.5 mg to be taken 12 hours apart. What is the most likely mechanism of action for this combined prescription?

Inhibition or delayed ovulation

Interference of corpus luteum function

Thickening of cervical mucus with sperm trapping

Tubal constriction inhibiting sperm transportation

Alteration of the endometrium impairing implantation of the fertilized egg

Cervical ripening methods for USMLE Step 3: High-Yield OB/GYN Lessons

Bishop Score - Go or No-Go?

Assesses cervical favorability for labor induction. A higher score predicts a higher likelihood of successful induction.

Components (0-3 points each):
- Cervical Dilation
- Cervical Effacement
- Fetal Station
- Cervical Position
- Cervical Consistency (Softness)

📌 Mnemonic: Bishop Is Super Helpful On Placement (Position, Effacement, Dilation, Station, Consistency)

Bishop Score Components Table

⭐ A Bishop score of ≥ 8 suggests the chances of a vaginal delivery after induction are similar to that of spontaneous labor. A score ≤ 5 is considered unfavorable, often requiring cervical ripening.

Mechanical Methods - Physical Pressure

Hygroscopic Dilators: Absorb ambient fluid and expand slowly.
- Laminaria japonica (dried seaweed), Dilapan-S® (synthetic polymer).
- Placed for 12-24 hours to gradually open the cervix.
- Lower infection risk than previously thought but can be uncomfortable.
Balloon Catheters: Apply direct mechanical pressure to the internal os, stimulating local prostaglandin release.
- Foley catheter: passed into the endocervix, inflated with 30-80 mL of saline.
- Cook® Double Balloon Catheter: one balloon in cervix, one in vagina.
- Left in place until it falls out (typically at 3-4 cm dilation).

⭐ Mechanical methods are preferred in patients with contraindications to prostaglandins (e.g., prior C-section) due to a significantly lower risk of uterine tachysystole.

Pharmacologic Methods - Chemical Nudges

Prostaglandins: Primary agents for cervical ripening.
- Mechanism: ↑ local inflammatory mediators → cervical softening & myometrial sensitization.
PGE1 Analog: Misoprostol (Cytotec)
- Routes: Oral, buccal, or vaginal.
- Dose: 25-50 mcg every 4-6 hours.
- Higher efficacy but also ↑ risk of uterine tachysystole (>5 contractions in 10 min).
- 📌 MisoProstol = More Potent.
PGE2 Analog: Dinoprostone
- Cervidil: Vaginal insert (10 mg) with controlled release. Easily removable if tachysystole occurs.
- Prepidil: Cervical gel (0.5 mg).
- Lower risk of tachysystole compared to Misoprostol.
Oxytocin (Pitocin):
- Less effective for ripening an unfavorable cervix (low Bishop score).
- Mainly used for labor induction or augmentation once the cervix is favorable.

⭐ Contraindication: Avoid prostaglandins in patients with a prior uterine scar (e.g., myomectomy, classical C-section) due to ↑ risk of uterine rupture.

Prostaglandins vs. Oxytocin: Uterine & Cervical Actions

High-Yield Points - ⚡ Biggest Takeaways

A Bishop score < 6 indicates an unfavorable cervix that requires ripening before induction.

Misoprostol (PGE1) is highly effective but carries a significant risk of uterine tachysystole.

Dinoprostone (PGE2) inserts can be removed if tachysystole occurs, offering more control.

Mechanical methods, like a Foley balloon, have a much lower risk of tachysystole.

Oxytocin augments labor but does not ripen an unfavorable cervix.

Prostaglandins are contraindicated with prior uterine surgery due to uterine rupture risk.

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