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 female at 32 weeks gestation presents to the emergency department with vaginal bleeding. She has had minimal prenatal care to-date with only an initial visit with an obstetrician after a positive home pregnancy test. She describes minimal spotting that she noticed earlier today that has progressed to larger amounts of blood; she estimates 30 mL of blood loss. She denies any cramping, pain, or contractions, and she reports feeling continued movements of the baby. Ultrasound and fetal heart rate monitoring confirm the presence of a healthy fetus without any evidence of current or impending complications. The consulted obstetrician orders blood testing for Rh-status of both the mother as well as the father, who brought the patient to the hospital. Which of the following represents the best management strategy for this situation?

If mother is Rh-negative and father is Rh-positive then administer RhoGAM

After 28 weeks gestation, administration of RhoGAM will have no benefit

If mother is Rh-positive and father is Rh-negative then administer RhoGAM

If mother is Rh-negative and father is Rh-negative then administer RhoGAM

If mother is Rh-negative and father is Rh-positive, RhoGAM administration is not needed

A 35-year-old woman gravida 2, para 1, comes to the physician for her first prenatal visit. Pregnancy and delivery of her first child were uncomplicated. She is not sure about the date of her last menstrual period. Pelvic examination shows a uterus consistent in size with a 10-week gestation. An ultrasound examination confirms the gestational age and shows one fetus with no indication of multiple gestations. During counseling on pregnancy risks and possible screening and diagnostic tests, the patient states she would like to undergo screening for Down syndrome. She would prefer immediate and secure screening with a low risk to herself and the fetus. Which of the following is the most appropriate next step in management at this time?

Nuchal translucency, pregnancy-associated plasma protein-A, human chorionic gonadotropin

Maternal serum α-fetoprotein, human chorionic gonadotropin, unconjugated estriol, and inhibin A

A 27-year-old G1P0 female presents for her first prenatal visit. She is in a monogamous relationship with her husband, and has had two lifetime sexual partners. She has never had a blood transfusion and has never used injection drugs. Screening for which of the following infections is most appropriate to recommend this patient?

Syphilis, HIV, HBV, and chlamydia

No routine screening is recommended for this patient

A 36-year-old primigravida presents to her obstetrician for antenatal care. She is at 24 weeks of gestation and does not have any current complaint except for occasional leg cramps. She does not smoke or drink alcohol. Family history is irrelevant. Her temperature is 36.9°C (98.42°F), blood pressure is 100/60 mm Hg, and pulse of 95/minute. Her body mass index is 21 kg/m² (46 pounds/m²). Physical examination reveals a palpable uterus above the umbilicus with no other abnormalities. Which of the following screening tests is suitable for this patient?

Oral glucose tolerance test for gestational diabetes mellitus

Fasting and random glucose testing for gestational diabetes mellitus

HbA1C for gestational diabetes mellitus

Complete blood count for iron deficiency anemia

Wet mount microscopy of vaginal secretions for bacterial vaginosis

A 25-year-old G1P0 woman at 22 weeks’ gestation presents to the emergency department with persistent vomiting over the past 8 weeks which has resulted in 5.5 kg (12.1 lb) of unintentional weight loss. She has not received any routine prenatal care to this point. She reports having tried diet modification and over-the-counter remedies with no improvement. The patient's blood pressure is 103/75 mm Hg, pulse is 93/min, respiratory rate is 15/min, and temperature is 36.7°C (98.1°F). Physical examination reveals an anxious and fatigued-appearing young woman, but whose findings are otherwise within normal limits. What is the next and most important step in her management?

Admit and begin intravenous rehydration

Begin treatment with vitamin B6

Begin treatment with metoclopramide

Obtain a basic electrolyte panel

Obtain a beta hCG and pelvic ultrasound

A 26-year-old woman presents to the women’s health clinic with a 9-week delay in menses. The patient has a history of grand mal seizures, and was recently diagnosed with acute sinusitis. She is prescribed lamotrigine and amoxicillin. The patient smokes one-half pack of cigarettes every day for 10 years, and drinks socially a few weekends every month. Her mother died of breast cancer when she was 61 years old. The vital signs are stable during the current office visit. Physical examination is grossly normal. The physician orders a urine beta-hCG that comes back positive. Abdominal ultrasound shows an embryo consistent in dates with the first day of last menstrual period. Given the history of the patient, which of the following would most likely decrease congenital malformations in the newborn?

Switching to another antiepileptic medication

Routine prenatal visit schedule for USMLE Step 3: High-Yield OB/GYN Lessons

Initial Prenatal Visit - The Grand Welcome

Comprehensive History & Physical:
- History: Detailed medical, surgical, OB/GYN (GPs), and genetic history.
- Physical Exam: Baseline weight, BMI, blood pressure, and a full pelvic exam including a Pap test if due.
Dating the Pregnancy:
- Based on Last Menstrual Period (LMP).
- 1st-trimester ultrasound is the most accurate method; Crown-Rump Length (CRL) measurement is key. Supersedes LMP if discrepancy is >7 days.
Initial Lab Workup (Prenatal Panel):
- Blood Tests: CBC, Blood type, Rh(D) status & antibody screen, RPR (syphilis), HBsAg (Hep B), HIV screen.
- Immunity Status: Rubella and Varicella titers.
- Infection Screen: Urine culture, Gonorrhea & Chlamydia NAAT.

⭐ A fetal heart rate is typically first detectable by Doppler ultrasound around 10-12 weeks of gestation.

First Trimester - Foundation & Formation

Frequency: Every 4 weeks.
Aneuploidy Screening (11-14 weeks):
- - Combined Test: Serum PAPP-A & β-hCG + Nuchal Translucency (NT) ultrasound.
- - NIPT/cffDNA: Non-invasive prenatal testing using cell-free fetal DNA; high sensitivity/specificity, especially for high-risk patients.
Diagnostic Testing (Confirmatory):
- - Chorionic Villus Sampling (CVS): Performed at 10-13 weeks if screening is positive or for high-risk cases.

Fetal Nuchal Translucency Ultrasound

⭐ Nuchal translucency (NT) is a key marker; an increased NT measurement is associated with a higher risk for aneuploidies like Trisomy 21.

Second Trimester - Anatomy & Sweetness

Visits: Every 4 weeks until 28 weeks.
Assessments: Monitor fetal heart tones & measure fundal height (pubic symphysis to uterine fundus).
Key Screenings & Diagnostics:
- 15-20 wks: Quad Screen (AFP, hCG, Estriol, Inhibin A).
- 15-20 wks: Amniocentesis for genetic diagnosis if indicated.
- 18-22 wks: Detailed anatomy ultrasound.
- 24-28 wks: Gestational Diabetes (GDM) screen with 50g, 1-hr glucose challenge test.

⭐ Quad Screen Pattern: In Down Syndrome (Trisomy 21), expect ↓ AFP, ↓ Estriol, but ↑ hCG and ↑ Inhibin A.

Third Trimester - The Final Countdown

Visit Frequency: Every 2 weeks from 28-36 weeks, then weekly from 36 weeks until delivery.
Key Assessments & Screenings:
- 28 weeks: Administer Rho(D) immune globulin if Rh-negative. Repeat CBC for anemia.
- 36-38 weeks: Group B Strep (GBS) rectovaginal culture.
- Assess fetal position and presentation via Leopold maneuvers.
- Consider repeat HIV/RPR for high-risk patients.

⭐ Intrapartum penicillin is indicated for GBS-positive status, unknown GBS status with risk factors (e.g., fever, prolonged rupture of membranes), or a history of an infant with invasive GBS disease.

Leopold maneuvers for fetal assessment

High-Yield Points - ⚡ Biggest Takeaways

Visit Frequency: Every 4 weeks until 28 weeks, every 2 weeks until 36 weeks, then weekly until delivery.

Initial Labs: Type & Rh, CBC, RPR, HIV, HBsAg, rubella immunity, GC/Chlamydia.

24-28 Weeks: Screen for gestational diabetes (1-hr GCT); give Rho(D) immune globulin to Rh-negative patients.

36-38 Weeks: Perform Group B Strep (GBS) rectovaginal culture.

Every Visit: Assess fetal heart tones and measure fundal height (after 20 weeks).

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