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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- First prenatal visit: confirm intrauterine pregnancy, date the pregnancy, screen risk factors, and obtain baseline prenatal labs
- Dating ultrasound is most accurate in the first trimester; crown-rump length is preferred before 14 weeks
- Routine labs include CBC, blood type/Rh, antibody screen, rubella, hepatitis B, hepatitis C, HIV, syphilis, urine culture, and STI testing when indicated
- Key timing: anatomy scan 18-22 weeks, GDM screen 24-28 weeks, Tdap 27-36 weeks, GBS culture 36 0/7-37 6/7 weeks
- Live vaccines are avoided during pregnancy; inactivated influenza vaccine is recommended in any trimester during flu season
Overview
Prenatal care is a structured preventive program designed to identify maternal disease, fetal risk, genetic concerns, infection, hypertensive disease, diabetes, alloimmunization, and social needs early enough to intervene. Pregnancy is dated from the first day of the last menstrual period, but first-trimester ultrasound provides the most accurate dating when dates are uncertain or discordant. USMLE Step 2 CK frequently asks which screening test or intervention is due at a specific gestational age.
Epidemiology
Most pregnancies are uncomplicated, but preventable morbidity is concentrated around hypertensive disease, gestational diabetes, infection, preterm birth, congenital anomalies, and hemorrhage. Early prenatal care improves the chance that these risks are identified before they become emergencies.
Clinical Features
Symptoms
Amenorrhea, nausea, breast tenderness, fatigue, urinary frequency, and mild pelvic fullness are common early symptoms
Light spotting can occur, but pain, heavy bleeding, or syncope requires urgent evaluation
Decreased fetal movement in the third trimester requires prompt fetal assessment
Severe headache, visual symptoms, RUQ pain, or dyspnea after 20 weeks suggests preeclampsia with severe features
Regular contractions, fluid leakage, or vaginal bleeding before term requires evaluation
Signs
Fundal height in centimeters approximates gestational age from 20-36 weeks
Fetal heart tones by Doppler are usually detectable from about 10-12 weeks
Normal pregnancy physiology includes mild tachycardia, increased plasma volume, and physiologic anemia
Blood pressure usually decreases in the second trimester then returns toward baseline near term
Fever, uterine tenderness, or purulent discharge with membrane rupture suggests intraamniotic infection
Investigations
First-line
Pregnancy confirmation and datingUrine or serum beta-hCG confirms pregnancy; transvaginal ultrasound confirms intrauterine location and dates pregnancy
Initial prenatal labsCBC, ABO/Rh, antibody screen, rubella immunity, hepatitis B surface antigen, hepatitis C, HIV, syphilis, urine culture, and varicella immunity if uncertain
STI testingGonorrhea and chlamydia for age/risk indications; repeat later if ongoing risk
Second-line
Aneuploidy screeningCell-free DNA from 10 weeks, first-trimester combined screening, quad screen, or diagnostic testing depending on risk and preference
Anatomy ultrasoundDetailed fetal anatomic survey at 18-22 weeks with placental location and amniotic fluid assessment
Gestational diabetes screeningUS two-step screen at 24-28 weeks: 50-g 1-hour glucose challenge then 100-g 3-hour OGTT if abnormal
Specialist
Maternal-fetal medicine referralMajor fetal anomaly, multiple gestation, significant maternal disease, severe preeclampsia, suspected FGR, or complex genetic risk
Invasive diagnostic testingCVS at 10-13 weeks or amniocentesis at >=15 weeks for definitive fetal genetic diagnosis
Management
ACOG Prenatal Care Guidance, USPSTF Preventive Recommendations, and ACOG Immunization Guidance1
Core prenatal care
- Confirm pregnancy location and gestational age early
- Assess age, prior obstetric history, chronic disease, medication exposures, substance use, safety, and social needs
- Monitor BP, weight, symptoms, fetal heart rate, fundal height after 20 weeks, and fetal movement awareness
- Counsel on nutrition, exercise, avoidance of alcohol/tobacco/recreational drugs, dental care, medication safety, and postpartum planning
2
Supplements and prevention
- Folic acid 400-800 mcg daily for all who could become pregnant; higher dose for selected high-risk patients
- Low-dose aspirin 81 mg daily from 12-28 weeks, ideally before 16 weeks, for high-risk preeclampsia prevention
- Rh-negative unsensitized patients receive Rh(D) immune globulin at 28 weeks and after sensitizing events
- Treat asymptomatic bacteriuria to reduce pyelonephritis and preterm birth risk
3
Vaccination
- Influenza vaccine in any trimester during flu season
- Tdap during every pregnancy at 27-36 weeks
- COVID-19 vaccination/boosters according to current guidance
- Avoid live vaccines such as MMR and varicella during pregnancy; give postpartum if nonimmune
4
Delivery planning
- Avoid elective delivery before 39 0/7 weeks without medical indication
- Discuss labor precautions, fetal movement, breastfeeding, contraception, and postpartum follow-up
- Postpartum care should include early contact and comprehensive assessment by 12 weeks
Complications
- Missed ectopic pregnancy: Early pregnancy pain or bleeding requires confirmation of intrauterine location
- Undetected hypertensive disease: Can progress to seizure, stroke, pulmonary edema, abruption, or HELLP syndrome
- Undiagnosed GDM: Increases macrosomia, shoulder dystocia, neonatal hypoglycemia, and future type 2 diabetes risk
- Rh alloimmunization: Preventable with Rh(D) immune globulin in unsensitized Rh-negative patients
- Congenital infection or anomaly: Requires targeted fetal assessment and specialist referral
USMLE Step 2 CK Exam Tips
- 1Best dating test in early pregnancy = first-trimester ultrasound crown-rump length
- 2Fundal height in cm approximates gestational age from 20-36 weeks
- 3GDM screening occurs at 24-28 weeks unless early testing for overt diabetes is indicated
- 4GBS culture is at 36 0/7-37 6/7 weeks
- 5Tdap is given during every pregnancy at 27-36 weeks
- 6Live vaccines are contraindicated in pregnancy
- 7Low-dose aspirin starts after 12 weeks for patients at high risk of preeclampsia
- 8Rh-negative unsensitized patient with bleeding, trauma, procedure, or 28-week visit = Rh(D) immune globulin
practicetest your knowledge on normal pregnancy & prenatal careApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — obstetrics & gynecology and beyond.
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