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 24-year-old woman comes to the physician for preconceptional advice. She has been married for 2 years and would like to conceive within the next year. Menses occur at regular 30-day intervals and last 4 days with normal flow. She does not smoke or drink alcohol and follows a balanced diet. She takes no medications. She is 160 cm (5 ft 3 in) tall and weighs 55 kg (121 lb); BMI is 21.5 kg/m2. Physical examination, including pelvic examination, shows no abnormalities. She has adequate knowledge of the fertile days of her menstrual cycle. Which of the following is most appropriate recommendation for this patient at this time?

Begin high-dose vitamin A supplementation

Begin vitamin B12 supplementation

A 24-year-old primigravida presents at 36 weeks gestation with vaginal bleeding, mild abdominal pain, and uterine contractions that appeared after bumping into a handrail. The vital signs are as follows: blood pressure 130/80 mm Hg, heart rate 79/min, respiratory rate 12/min, and temperature 36.5℃ (97.7℉). The fetal heart rate was 145/min. Uterine fundus is at the level of the xiphoid process. Slight uterine tenderness and contractions are noted on palpation. The perineum is bloody. The gynecologic examination shows no vaginal or cervical lesions. The cervix is long and closed. Streaks of bright red blood are passing through the cervix. A transabdominal ultrasound shows the placenta to be attached to the lateral uterine wall with a marginal retroplacental hematoma (an approximate volume of 150 ml). The maternal hematocrit is 36%. What is the next best step in the management of this patient?

Admit for maternal and fetal monitoring and observation

Manage as an outpatient with modified rest

Corticosteroid administration and schedule a cesarean section after

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 27-year-old G0P0 female presents to her OB/GYN for a preconception visit to seek advice before becoming pregnant. A detailed history reveals no prior medical or surgical history, and she appears to be in good health currently. Her vaccination history is up-to-date. She denies tobacco or recreational drug use and admits to drinking 2 glasses of wine per week. She states that she is looking to start trying to become pregnant within the next month, hopefully by the end of January. Which of the following is NOT recommended as a next step for this patient's preconception care?

Administer measles, mumps, rubella (MMR) vaccination

Begin 400 mcg folic acid supplementation

Recommend inactivated influenza vaccination

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 21-year-old G2P1 woman presents to the clinic and is curious about contraception immediately after her baby is born. She is anxious about taking care of one child and does not believe that she can handle the responsibility of caring for another. She has no other questions or complaints today. Her past medical history consists of generalized anxiety disorder, antithrombin deficiency, and chronic deep vein thrombosis. She has been hospitalized for acute on chronic deep vein thrombosis. Her only medication is buspirone. Her blood pressure is 119/78 mm Hg and the heart rate is 78/min. BMI of the patient is 32 kg/m2. On physical examination, her fundal height is 21 cm from pubic symphysis. No ovarian masses are palpated during the bimanual examination. Ultrasound exhibits a monoamniotic, monochorionic fetus. Which of the following forms of contraception would be the most detrimental given her risk factors?

Transdermal contraceptive patch

Depot medroxyprogesterone acetate

Prior preterm birth management for USMLE Step 3: High-Yield OB/GYN Lessons

Risk Stratification - Spotting Trouble Early

History is Paramount: The single greatest risk factor is a prior spontaneous preterm birth (sPTB).
- Risk ↑ with the number of prior sPTBs and the earliness of those deliveries.
Cervical Length (CL) Screening:
- Assessed via transvaginal ultrasound (TVUS) between 16-24 weeks.
- A short cervix (CL < 25 mm) is the key predictive finding.

Transvaginal ultrasound of shortened cervix (2.09 cm)

⭐ A history of a single prior spontaneous preterm birth at <34 weeks increases the risk for a subsequent preterm birth by approximately 3-fold.

Interventions - Progesterone & Cerclage

Progesterone Supplementation
- Indication: Singleton pregnancy with a history of prior spontaneous preterm birth (sPTB).
- Regimen: Start 17-OHPC or vaginal progesterone at 16-24 weeks, continue until 36 weeks. Reduces risk of recurrent PTB.
Cervical Cerclage
- Indications:
  - History-indicated: ≥1 prior 2nd-trimester loss from painless dilation.
  - Ultrasound-indicated: Prior sPTB + short cervix (CL < 25 mm) before 24 weeks.
- Timing: Placed at 12-14 weeks (history) or up to 24 weeks (ultrasound). Removed at ~37 weeks.

Transabdominal and Transvaginal Cerclage Procedures

⭐ High-Yield: Cerclage is NOT indicated for a short cervix found on ultrasound without a prior history of preterm birth. It is also not recommended for multiple gestations as it may increase the risk of preterm birth.

Management Algorithm - The Preterm Playbook

Threatened Preterm Labor Management Algorithm

Patient Profile: Singleton pregnancy with a history of prior spontaneous preterm birth (sPTB).
Core Strategy: Progesterone supplementation & cervical length (CL) monitoring.

⭐ Cerclage is only indicated for a short cervix (<25 mm) in a patient with a history of prior preterm birth. For an incidental short cervix without a prior history, progesterone alone is the standard of care.

Special Cases - Twins & Rescues

Twin Gestation & Prior PTB:
- Progesterone (vaginal or 17-OHPC) is not effective in preventing preterm birth in twins and is not recommended.
- Cerclage for a short cervix ($<25$ mm before 24 weeks) is controversial; its benefit is less clear than in singleton pregnancies.
Rescue (Emergent) Cerclage:
- Performed for painless cervical dilation discovered on physical exam in the second trimester.
- Goal is to physically close the cervix to prolong gestation.

⭐ In stark contrast to singleton pregnancies, progesterone supplementation has not been shown to reduce the risk of preterm birth in women with twin gestations.

Cervical Cerclage Illustration

High‑Yield Points - ⚡ Biggest Takeaways

Prior preterm birth is the strongest predictor for future preterm labor.

Management is guided by serial cervical length measurements between 16-24 weeks.

A history of preterm birth plus a short cervix (<2.5 cm) indicates a cerclage.

With a normal cervix length, give prophylactic 17-hydroxyprogesterone from 16 weeks.

For an incidental short cervix without a prior history, use vaginal progesterone.

Administer antenatal corticosteroids for threatened delivery <37 weeks.

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