A 24-year-old woman visits her physician to seek preconception advice. She is recently married and plans to have a child soon. Menses occur at regular 28-day intervals and last 5 days. She has sexual intercourse only with her husband and, at this time, they consistently use condoms for birth control. The patient consumes a well-balanced diet with moderate intake of meat and dairy products. She has no history of serious illness and takes no medications currently. She does not smoke or drink alcohol. The patient’s history reveals no birth defects or severe genetic abnormalities in the family. Physical examination shows no abnormalities. Pelvic examination indicates a normal vagina, cervix, uterus, and adnexa. To decrease the likelihood of fetal neural-tube defects in her future pregnancy, which of the following is the most appropriate recommendation for initiation of folic acid supplementation?

As soon as her pregnancy is confirmed

No folic acid supplement is required as nutritional sources are adequate

In the second half of pregnancy

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 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 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

A 34-year-old primigravid woman comes to the physician for a prenatal visit at 37-weeks' gestation because of worsening back pain for 3 weeks. The pain is worse with extended periods of walking, standing, and sitting. She has not had any changes in bowel movements or urination. Her mother has rheumatoid arthritis. Examination of the back shows bilateral pain along the sacroiliac joint area as a posterior force is applied through the femurs while the knees are flexed. She has difficulty actively raising either leg while the knee is extended. Motor and sensory function are normal bilaterally. Deep tendon reflexes are 2+. Babinski sign is absent. Pelvic examination shows a uterus consistent in size with a 37-weeks' gestation. There is no tenderness during abdominal palpation. Which of the following is the most likely explanation for this patient's symptoms?

Relaxation of the pelvic girdle ligaments

Vertebral bone compression fracture

Patient education topics for USMLE Step 3: High-Yield OB/GYN Lessons

Nutrition & Supplements - Eating For Two

Caloric Intake: Modest increase; not "eating for two."
- ↑ ~340 kcal/day in 2nd trimester.
- ↑ ~450 kcal/day in 3rd trimester.
Core Supplements:
- Folic Acid: 0.4-0.8 mg/day (preconception/1st tri) to prevent Neural Tube Defects (NTDs).
- Iron: 27 mg/day for Hb synthesis and to prevent anemia.
- Calcium: 1000-1300 mg/day for fetal bone/teeth.
Foods to Avoid (Risk of Listeria, Mercury, Toxoplasma):
- Unpasteurized dairy, deli meats, hot dogs.
- High-mercury fish (e.g., swordfish, king mackerel).
- Raw/undercooked seafood, eggs, and meat.

⭐ For patients with a prior NTD-affected pregnancy or on anti-seizure medication (e.g., valproate, carbamazepine), the folic acid dose is much higher: 4 mg/day.

Lifestyle & Teratogens - The Pregnancy No‑Fly Zone

Alcohol: No safe amount. Risk of Fetal Alcohol Syndrome (FAS).
- Features: Smooth philtrum, thin vermilion border, small palpebral fissures.
Tobacco: ↑ risk of IUGR, preterm labor, placental abruption.
Caffeine: Limit to < 200 mg/day.
Radiation: Fetal risk > 5 rads. Most diagnostic imaging is safe.
Key Teratogens:
- ACE Inhibitors/ARBs: Renal defects.
- Isotretinoin: Severe craniofacial, CNS, cardiac defects.
- Warfarin: Nasal hypoplasia, stippled epiphyses.
- Valproate: Neural tube defects (e.g., spina bifida).
- Lithium: Ebstein anomaly.
- Tetracyclines: Teeth staining.

Fetal Alcohol Syndrome: Key Facial Features

⭐ Use of valproate for seizures or bipolar disorder during pregnancy significantly increases the risk of neural tube defects.

Screening & Testing - The Trimester Checklist

First Trimester (Weeks 1-12)
- Initial Labs: CBC, Rh type, HIV, HBsAg, RPR, Rubella, GC/Chlamydia.
- Aneuploidy Screen (11-13 wks): PAPP-A, β-hCG, nuchal translucency (NT).
- Cell-free fetal DNA (cffDNA) >10 wks.
- CVS for definitive diagnosis.
Second Trimester (Weeks 13-27)
- Quad Screen (15-22 wks): AFP, estriol, β-hCG, inhibin A.
- Anatomy Scan (18-20 wks).
- Glucose Challenge Test (GCT) (24-28 wks): 50g glucose load.
Third Trimester (Weeks 28-40)
- Rho(D) immune globulin at 28 wks if Rh-negative.
- GBS Screen (36-38 wks): Rectovaginal culture.

Pregnancy Check-ins & Testing Timeline by Trimester

⭐ Down Syndrome (Trisomy 21) Quad Screen: ↓ AFP, ↓ Estriol, ↑ β-hCG, ↑ Inhibin A.

Warning Signs & Discomforts - Red Flags & Growing Pains

Normal Discomforts (Physiologic)
- Nausea/Vomiting, heartburn, constipation
- Mild ankle edema, varicose veins
- Low back pain, pelvic girdle pain
- Braxton Hicks: irregular, non-progressing contractions
⚠️ Warning Signs (Red Flags) → Seek Immediate Care
- Vaginal bleeding or fluid leakage
- Severe headache, visual disturbances (scotomata)
- Persistent, severe abdominal pain or regular contractions
- Decreased or absent fetal movement
- Fever >38°C (100.4°F) or chills
- Severe swelling (face, hands), sudden weight gain

⭐ Preeclampsia Triad: New-onset hypertension after 20 weeks gestation, plus proteinuria OR signs of end-organ damage (e.g., severe headache, visual changes, RUQ pain).

High‑Yield Points - ⚡ Biggest Takeaways

Folic acid prevents neural tube defects; high-risk patients need 4 mg/day, while average-risk need 0.4-0.8 mg/day.

Weight gain targets are based on pre-pregnancy BMI (normal BMI target: 25-35 lbs).

Avoid unpasteurized foods (Listeria), undercooked meat (Toxoplasma), and high-mercury fish.

There is no safe amount of alcohol; counsel complete cessation of tobacco and illicit drugs.

Key teratogenic medications to stop include ACE inhibitors, ARBs, warfarin, and valproate.

Teach warning signs: severe headache, vision changes, vaginal bleeding, or decreased fetal movement.

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