Prenatal Care: MCCQE1 Study Guide

Introduction

Prenatal care is a cornerstone of Obstetrics and a high-yield topic for the MCCQE1. In the Canadian context, prenatal care is guided largely by the Society of Obstetricians and Gynaecologists of Canada (SOGC). The primary goal is to ensure the best possible health outcomes for the dyad (mother and fetus) through risk assessment, health promotion, and medical intervention.

As a future Canadian physician, you must embody the CanMEDS Health Advocate role, ensuring equitable access to screening and preventative measures.

Pre-conception Counseling

Ideally, care begins before conception. This allows for the optimization of maternal health.

Key Pre-conception Actions

• Medication Review: Switch teratogenic meds (e.g., ACE inhibitors, Valproic acid, Warfarin) to safer alternatives.
• Chronic Disease Management: Optimize control of HTN, Diabetes (aim for HbA1c <6.5% or <7.0% depending on hypoglycemia risk), and Thyroid disease.
• Screening: Rubella immunity, Varicella immunity, HIV, Hepatitis B, Syphilis.

The Initial Prenatal Visit

The first visit usually occurs between 8–12 weeks. The objectives are to confirm pregnancy, establish gestational age, and risk stratify.

1. History Taking

• Menstrual History: First day of Last Menstrual Period (LMP).
• Obstetric History (GTPAL): Gravida, Term, Preterm, Abortions, Living.
• Medical/Surgical History: Focus on uterine surgeries (C-section, myomectomy).
• Social History: Smoking, Alcohol (Recommend complete abstinence), Intimate Partner Violence (IPV) screening.

2. Dating the Pregnancy

Accurate dating is crucial for screening windows and induction decisions.

# Naegele's Rule Calculation
EDD = (LMP + 7 days) - 3 months + 1 year

• Clinical Standard: First trimester ultrasound (Crown-Rump Length or CRL) is the most accurate method for dating.
  • If CRL dating differs from LMP dating by >5 days (up to 12 weeks) or >7 days (12-20 weeks), use the Ultrasound date.

3. Initial Investigations

Routine Prenatal Visit Schedule

In an uncomplicated pregnancy, the standard Canadian schedule is:

Standard Assessments at Every Visit

1. Maternal Well-being: BP, Weight, Urine dipstick (proteinuria - debatable utility but often done), Symptoms (bleeding, leakage of fluid, headache).
2. Fetal Well-being:
   • Fetal Heart Rate (FHR) via Doppler (starting 10-12 weeks).
   • Symphysis-Fundal Height (SFH) in cm (starting 20 weeks).
     • Normal: SFH = Weeks of gestation $\pm$ 2 cm.

Trimester-Specific Screening & Interventions

This section is critical for MCCQE1 preparation, as questions often target specific gestational windows.

First Trimester (0–13 weeks)

Genetic Screening (Aneuploidy)

Canadian guidelines recommend offering screening for trisomy 21, 13, and 18 to all pregnant women.

• FTS (First Trimester Screening): 11–14 weeks. Includes Nuchal Translucency (NT) ultrasound + PAPP-A + free $\beta$-hCG.
• NIPT (Non-Invasive Prenatal Testing): Analysis of cell-free fetal DNA in maternal blood.
  • Highest sensitivity and specificity.
  • Provincial funding varies (often funded if age >40 or positive FTS).
• CVS (Chorionic Villus Sampling): Diagnostic test offered if screening is high risk (11–13 weeks).

Second Trimester (14–26 weeks)

1. Genetic Screening (if missed first trimester)

• MSS (Maternal Serum Screen) / Quad Screen: 15–20 weeks (AFP, uE3, hCG, Inhibin A).

2. Detailed Anatomy Scan

• Timing: 18–22 weeks.
• Purpose: Placental location, fetal anatomy, amniotic fluid volume.

3. Gestational Diabetes Mellitus (GDM) Screening

• Timing: 24–28 weeks.
• Method: SOGC prefers the Two-Step Approach.

Third Trimester (27–40 weeks)

1. Rh Immune Globulin (WinRho)

• Timing: 28 weeks.
• Indication: All Rh-negative women with negative antibody screen.
• Also give if: Bleeding, trauma, ECV, or amniocentesis.

2. Group B Streptococcus (GBS) Screening

• Timing: 35–37 weeks.
• Method: Vaginal-rectal swab.
• Positive Result: Intrapartum antibiotic prophylaxis (IV Penicillin G) required.
• Bacteriuria: Any GBS bacteriuria during pregnancy = Treat at time of diagnosis AND automatic intrapartum prophylaxis (no swab needed at 35w).

3. Fetal Movement Counting

• Advise women to start counting kicks daily from 26–32 weeks (depending on risk).
• Guideline: < 6 movements in 2 hours warrants further assessment (NST/BPP).

Common Issues and Canadian Management

Nausea and Vomiting of Pregnancy (NVP)

• Lifestyle: Small frequent meals, ginger.
• Pharmacotherapy: Uniquely Canadian first-line is Doxylamine/Pyridoxine (Diclectin).

Hypertension

• Chronic HTN: Present before 20 weeks.
• Gestational HTN: New onset BP ≥ 140/90 after 20 weeks, no proteinuria.
• Preeclampsia: HTN + Proteinuria or end-organ dysfunction.
• Prophylaxis: SOGC recommends ASA 81–162 mg daily at bedtime starting 12–16 weeks for women at high risk of preeclampsia.

Vaccinations

• Influenza: Recommended in any trimester during flu season.
• Tdap (Pertussis): Recommended in every pregnancy (ideally 21–32 weeks) to provide passive immunity to the newborn against whooping cough.
• Live vaccines (MMR, Varicella): Contraindicated during pregnancy.

Key Points to Remember for MCCQE1

Sample Question

Clinical Scenario

A 28-year-old G1P0 woman presents to the clinic for a routine prenatal visit at 26 weeks gestation. She has no significant past medical history. Her pre-pregnancy BMI was 29 kg/m². Her blood pressure is 118/74 mmHg. She reports good fetal movement. As part of her routine care, you are discussing screening for gestational diabetes.

Question

Which one of the following is the most appropriate next step in the management of this patient according to Canadian guidelines?

Options

• A. Measure random glucose; if >11.1 mmol/L, diagnose gestational diabetes.
• B. Order a fasting plasma glucose and Hemoglobin A1c.
• C. Administer a 50g oral glucose challenge test (non-fasting).
• D. Administer a 75g oral glucose tolerance test (fasting).
• E. Reassure her that screening is not necessary as she has no family history of diabetes.

Explanation

The correct answer is:

• C. Administer a 50g oral glucose challenge test (non-fasting).

Detailed Explanation: The SOGC Clinical Practice Guideline on Diabetes in Pregnancy recommends universal screening for Gestational Diabetes Mellitus (GDM) between 24 and 28 weeks of gestation.

• Option C is correct: The SOGC preferred approach is the Two-Step approach. The first step is the 50g Glucose Challenge Test (GCT), which is done in the non-fasting state.
  • If the 1-hour plasma glucose is < 7.8 mmol/L, GDM is ruled out.
  • If it is 7.8 – 11.0 mmol/L, the patient proceeds to the 75g OGTT (Step 2).
  • If it is ≥ 11.1 mmol/L, GDM is diagnosed.
• Option A is incorrect: Random glucose is not the standard screening test for GDM.
• Option B is incorrect: While HbA1c and fasting glucose are useful for detecting overt diabetes early in pregnancy, they are not the standard screening tests for gestational diabetes at 24-28 weeks due to lower sensitivity for GDM specifically compared to the glucose load tests.
• Option D is incorrect: The 75g OGTT is the second step in the preferred Canadian protocol (or the only step in the “One-Step” IADPSG protocol, which is an alternative but not the preferred standard for SOGC at the time of most recent major guidelines). It requires fasting.
• Option E is incorrect: Universal screening is recommended for all pregnant women in Canada, regardless of risk factors.

References

1. Society of Obstetricians and Gynaecologists of Canada (SOGC). Diabetes in Pregnancy. Clinical Practice Guideline No. 393. J Obstet Gynaecol Can 2019.
2. Society of Obstetricians and Gynaecologists of Canada (SOGC). Immunization in Pregnancy. Clinical Practice Guideline No. 364.
3. Public Health Agency of Canada. The Sensible Guide to a Healthy Pregnancy.
4. Magee LA, et al. Diagnosis, Evaluation, and Management of the Hypertensive Disorders of Pregnancy: Executive Summary. J Obstet Gynaecol Can 2014.
5. Wilson, R.D., et al. Prenatal Screening for Fetal Aneuploidy in Singleton Pregnancies. SOGC Clinical Practice Guideline. J Obstet Gynaecol Can 2015.