A 38-year-old woman, gravida 3, para 2, at 12 weeks' gestation comes to her obstetrician for a prenatal visit. Screening tests in the first trimester showed a decreased level of pregnancy-associated plasma protein and an increased level of β-hCG. A genetic disorder is suspected. Which of the following results from an additional diagnostic test is most likely to confirm the diagnosis?

Trisomy 21 on chorionic villus sampling

Decreased estriol in maternal serum

Increased inhibin A in maternal serum

Increased nuchal translucency on ultrasound

A 19-year-old woman presents for a sports physical. She says she feels healthy and has no concerns. Past medical history is significant for depression and seasonal allergies. Current medications are fluoxetine and oral estrogen/progesterone contraceptive pills. Family history is significant for a sister with polycystic ovarian syndrome (PCOS). The patient denies current or past use of alcohol, recreational drugs, or smoking. She reports that she has been on oral birth control pills since age 14 and uses condoms inconsistently. No history of STDs. She is sexually active with her current boyfriend, who was treated for chlamydia 2 years ago. She received and completed the HPV vaccination series starting at age 11. Her vital signs include: temperature 36.8°C (98.2°F), pulse 97/min, respiratory rate 16/min, blood pressure 120/75 mm Hg. Physical examination is unremarkable. Which of the following are the recommended guidelines for cervical cancer screening for this patient at this time?

No cervical cancer screening is indicated at this time

Cytology (pap smear) and HPV DNA co-testing every 3 years

Cytology (pap smear) every 3 years

Cytology (pap smear) and HPV DNA co-testing every 5 years

A mother presents to the family physician with her 16-year-old son. She explains, "There's something wrong with him doc. His grades are getting worse, he's cutting class, he's gaining weight, and his eyes are often bloodshot." Upon interviewing the patient apart from his mother, he seems withdrawn and angry at times when probed about his social history. The patient denies abuse and sexual history. What initial test should be sent to rule out the most likely culprit of this patient's behavior?

Sexually transmitted infection (STI) testing

A 36-year-old G3P2002 presents to her obstetrician’s office for her first prenatal visit at ten weeks and two days gestation. She notes that she has felt nauseous the last several mornings and has been especially tired for a few weeks. Otherwise, she feels well. The patient has had two uncomplicated spontaneous vaginal deliveries at full term with her last child born six years ago. She is concerned about the risk of Down syndrome in this fetus, as her sister gave birth to an affected child at age 43. The patient has a history of generalized anxiety disorder, atopic dermatitis, and she is currently on escitalopram. At this visit, this patient’s temperature is 98.6°F (37.0°C), pulse is 70/min, blood pressure is 121/67 mmHg, and respirations are 13/min. The patient appears anxious, but overall comfortable, and cardiopulmonary and abdominal exams are unremarkable. Pelvic exam reveals normal female external genitalia, a closed and slightly soft cervix, a ten-week-sized uterus, and no adnexal masses. Which of the following is the best next step for definitively determining whether this patient’s fetus has Down syndrome?

Genetic testing of patient’s sister

First trimester screening for USMLE Step 2 CK: High-Yield OB/GYN Lessons

First Trimester Screen - The Early Peek

When: 11-14 weeks gestation.
Components:
- Maternal Serum: Pregnancy-associated plasma protein-A (PAPP-A) & free β-hCG.
- Ultrasound: Nuchal Translucency (NT).
Screens for: Aneuploidies, primarily Trisomy 21 & 18.
Abnormal Patterns:
- Trisomy 21: ↓ PAPP-A, ↑ β-hCG, ↑ NT. (📌 Mnemonic: Down syndrome has High hCG).
- Trisomy 18: ↓ PAPP-A, ↓ β-hCG, ↑ NT.

Fetal Nuchal Translucency Ultrasound Measurement

⭐ The "combined test" (this screen + maternal age) detects ~85% of Down syndrome cases. A positive screen is NOT diagnostic; it indicates increased risk requiring further testing.

Screening Components - The Telltale Trio

Combined first-trimester screening (cFTS) integrates ultrasound findings with maternal serum analytes between 11-14 weeks gestation to calculate aneuploidy risk.

Nuchal Translucency (NT) on Ultrasound
- Measures subcutaneous fluid at the back of the fetal neck.
- ↑ NT suggests increased risk for aneuploidies (Trisomy 21, 18) and cardiac defects.
Maternal Serum Analytes
- ↓ PAPP-A (Pregnancy-Associated Plasma Protein-A): Low levels are a consistent marker for Trisomy 21 & 18.
- ↑ free β-hCG (human Chorionic Gonadotropin): Significantly elevated in Trisomy 21; decreased in Trisomy 18.

⭐ The combination of NT, PAPP-A, and β-hCG achieves a detection rate of approximately 85% for Down syndrome.

Interpreting Results - Trisomy Telltales

Combined First Trimester Screening (CFTS): Integrates Nuchal Translucency (NT) ultrasound with maternal serum markers (PAPP-A, free β-hCG) to calculate an adjusted aneuploidy risk.

Aneuploidy	Nuchal Translucency (NT)	PAPP-A	Free β-hCG
Trisomy 21 (Down)	↑	↓	↑↑
Trisomy 18 (Edwards)	↑	↓↓	↓↓
Trisomy 13 (Patau)	↑	↓↓	↓↓

📌 Mnemonic: For T21, remember HI-CG & HI-NT (hCG and NT are HIgh). For T18/13, all markers are profoundly Low.

⭐ Isolated low PAPP-A in the first trimester is a significant marker for adverse pregnancy outcomes like pre-eclampsia, fetal growth restriction, and stillbirth, even with a normal fetal karyotype.

Positive Screen Path - What Now?

A positive screen requires patient counseling on risks and options. The choice is between proceeding directly to invasive diagnostic testing or opting for non-invasive cell-free fetal DNA (cffDNA) screening first, which has higher sensitivity and specificity.

⭐ Definitive diagnosis requires fetal genetic material. Screening tests only assess risk; they are not diagnostic. Both CVS and amniocentesis carry a small risk of miscarriage.

Amniocentesis vs. Chorionic Villus Sampling

High‑Yield Points - ⚡ Biggest Takeaways

First-trimester screening assesses risk for aneuploidies, mainly Trisomies 21, 18, and 13.

It combines maternal serum analytes (free β-hCG, PAPP-A) with an ultrasound for nuchal translucency (NT).

Performed between 11 and 14 weeks gestation.

Trisomy 21 findings: ↑ NT, ↑ free β-hCG, and ↓ PAPP-A.

Trisomy 18/13 findings: ↑ NT with ↓ free β-hCG and ↓ PAPP-A.

This is a screening test, not diagnostic; abnormal results require confirmatory testing (CVS or amniocentesis).

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