Study guide
13.3 Thyroid Disease & Venous Thromboembolism in Pregnancy
ABIM Internal Medicine Exam
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1 Chapter 0: The ABIM Exam, Blueprint & Study Strategy
0.1 Exam Format, Question Types & the 2026 Blueprint 0.2 Eligibility, Registration, Fees & Exam-Day Logistics 0.3 Scoring, the Passing Standard & Score Reports 0.4 Building a Blueprint-Weighted Study Plan
2 Chapter 1: Cardiovascular Disease (14% of Exam)
1.1 Ischemic Heart Disease & Acute Coronary Syndromes 1.2 Antithrombotic Therapy, Secondary Prevention & Mechanical Complications of MI 1.3 Atrial Fibrillation, Atrial Flutter & Stroke Prevention 1.4 Supraventricular Tachycardias, Ventricular Arrhythmias & Bradycardias 1.5 Heart Failure: Classification, Staging & Guideline-Directed Medical Therapy 1.6 Device Therapy, HFpEF & the Cardiomyopathies 1.7 Valvular Heart Disease & Endocarditis Prophylaxis 1.8 Pericardial Disease & Acute Aortic Syndromes 1.9 Hypertension: Classification, Diagnosis & Secondary Causes 1.10 Hypertensive Crises & Dyslipidemia 1.11 Adult Congenital Heart Disease & Coarctation of the Aorta 1.12 Syncope: Reflex, Orthostatic & Cardiac Causes 1.13 Cardiac Physical Examination, Murmurs & Antithrombotic Selection
3 Chapter 2: Endocrinology, Diabetes & Metabolism (9% of Exam)
2.1 Diabetes Mellitus: Diagnosis, Glycemic Targets & Pharmacotherapy 2.2 Insulin Therapy, Hyperglycemic Emergencies & Chronic Complications 2.3 Thyroid Function Testing & Hypothyroidism 2.4 Thyrotoxicosis, Thyroid Storm & Thyroid Nodules 2.5 Adrenal & Pituitary Disorders 2.6 Hypercalcemia, Hypocalcemia & Disorders of Mineral Metabolism 2.7 Osteoporosis & Paget Disease of Bone 2.8 Ovarian, Testicular & Reproductive Endocrine Disorders 2.9 Hypoglycemia, Endocrine Tumors, Polyglandular Syndromes & Severe Hypertriglyceridemia
4 Chapter 3: Gastroenterology & Hepatology (9% of Exam)
3.1 Esophageal Disease 3.2 Stomach & Duodenal Disease and Gastrointestinal Hemorrhage 3.3 Inflammatory Bowel Disease 3.4 Celiac Disease & Irritable Bowel Syndrome 3.5 Diverticular Disease & Colorectal Cancer Screening 3.6 Viral Hepatitis, Steatotic & Alcohol-Associated Liver Disease 3.7 Cirrhosis & the Complications of Portal Hypertension 3.8 Acute Pancreatitis 3.9 Chronic Pancreatitis & Biliary Tract Disease 3.10 Inherited, Autoimmune & Drug-Induced Liver Disease 3.11 Small Intestinal Disease, Ischemia & Gastrointestinal Complications of HIV
5 Chapter 4: Infectious Disease (9% of Exam)
4.1 Lower Respiratory Tract Infections & Sepsis Syndromes 4.2 Viral Respiratory Pathogens & Tuberculosis 4.3 Central Nervous System Infections 4.4 Skin, Soft Tissue, Bone & Joint Infections 4.5 Infective Endocarditis & Cardiovascular Infection 4.6 Clostridioides difficile & Catheter-Related Bloodstream Infection 4.7 HIV Diagnosis, Antiretroviral Therapy & Prevention 4.8 Opportunistic Infections & Sexually Transmitted Infections 4.9 Fever of Unknown Origin, Neutropenic Fever & Toxic Shock 4.10 Travel-Related Illness, Vector-Borne Disease & Outbreaks 4.11 Infection Prevention, Nosocomial Infection & Postexposure Prophylaxis 4.12 Rheumatic Fever, Poststreptococcal Disease, Enteric & Hepatic Infections
6 Chapter 5: Pulmonary Disease (9% of Exam)
5.1 COPD: Diagnosis, GOLD Classification & Initial Pharmacotherapy 5.2 Interventions That Reduce COPD Mortality & Exacerbation Management 5.3 Asthma: Diagnosis, Stepwise Therapy & Status Asthmaticus 5.4 Interstitial Lung Disease & Idiopathic Pulmonary Fibrosis 5.5 Sarcoidosis, Hypersensitivity Pneumonitis & Occupational Lung Disease 5.6 Pulmonary Embolism: Diagnosis, Risk Stratification & Anticoagulation 5.7 Pulmonary Hypertension & Sleep-Disordered Breathing 5.8 Acute Respiratory Distress Syndrome & Mechanical Ventilation 5.9 Pleural Disease, Empyema & Pneumothorax 5.10 Bronchiectasis, Cystic Fibrosis & Restrictive Lung Disease 5.11 Evaluation of Cough, Dyspnea, Hemoptysis & the Solitary Pulmonary Nodule
7 Chapter 6: Rheumatology & Orthopedics (9% of Exam)
6.1 Rheumatoid Arthritis: Diagnosis & Systemic Manifestations 6.2 Antirheumatic Pharmacotherapy & the Spondyloarthropathies 6.3 Gout: Pathophysiology & Acute Management 6.4 Urate-Lowering Therapy & Calcium Pyrophosphate Deposition Disease 6.5 Osteoarthritis 6.6 Systemic Lupus Erythematosus 6.7 Systemic Sclerosis, Sjogren Syndrome & Inflammatory Myopathies 6.8 The Vasculitides 6.9 Regional Musculoskeletal Syndromes, Back Pain & Sports Injuries 6.10 Other Primary Rheumatic Disorders & Mixed Connective Tissue Disease 6.11 Osteonecrosis & Metabolic Bone Disease
8 Chapter 7: Hematology (6% of Exam)
7.1 Approach to Anemia & the Microcytic Anemias 7.2 Macrocytic, Normocytic & Hemolytic Anemias 7.3 Hemoglobinopathies, Thalassemias & Paroxysmal Nocturnal Hemoglobinuria 7.4 Platelet Disorders, Thrombocytopenia & the Bleeding Patient 7.5 Coagulation Factor Disorders, Thrombophilia & Anticoagulant Reversal 7.6 Acute Leukemias, Chronic Leukemias & Myeloproliferative Neoplasms 7.7 Lymphomas & Plasma Cell Disorders 7.8 Myelodysplastic Syndrome, Myeloproliferative Neoplasms & Porphyria 7.9 Transfusion Medicine & Late Complications of Transplantation
9 Chapter 8: Medical Oncology (6% of Exam)
8.1 Breast, Lung, Colorectal & Prostate Cancer 8.2 Oncologic Emergencies 8.3 Genitourinary & Gynecologic Malignancies 8.4 Head and Neck, Bone & Soft Tissue Cancer and Cancer of Unknown Primary 8.5 Complications of Cancer & Its Treatment 8.6 Cancer Prevention, Survivorship & Psychosocial Care
10 Chapter 9: Nephrology & Urology (6% of Exam)
9.1 Acute Kidney Injury: Staging, Etiology & Urine Microscopy 9.2 Glomerular Disorders & Nephrotic Syndrome 9.3 Nephritic Syndromes, RPGN & Indications for Renal Replacement Therapy 9.4 Chronic Kidney Disease: Staging & Progression Retardation 9.5 Complications of Chronic Kidney Disease: Anemia, CKD-MBD & Acidosis 9.6 Hyponatremia, Hypernatremia & Water Balance 9.7 Potassium Disorders & Systematic Acid-Base Analysis 9.8 Renal Tubular Acidosis & Nephrolithiasis 9.9 Prostate Disorders, Urinary Incontinence & Other Urologic Conditions 9.10 Cystic Kidney Disease, Obstructive Uropathy, Tubulointerstitial Disease & Hematuria
11 Chapter 10: Neurology (4% of Exam)
10.1 Acute Ischemic Stroke: Syndromes & Reperfusion 10.2 Transient Ischemic Attack, Secondary Prevention & Hemorrhagic Stroke 10.3 Headache & Facial Pain 10.4 Seizures, Epilepsy & Movement Disorders 10.5 Multiple Sclerosis & Neuromuscular Junction Disorders 10.6 Motor Neuron Disease & Acute Peripheral Neuropathy 10.7 Cranial Neuropathies & Neuro-Ophthalmology 10.8 Peripheral Neuropathies, CNS Tumors & Other Neurologic Disorders
12 Chapter 11: Psychiatry & Behavioral Health (4% of Exam)
11.1 Major Depressive Disorder & Medical Mimics 11.2 Antidepressant Pharmacotherapy & Treatment-Resistant Depression 11.3 Bipolar Disorder, Mood Stabilizers & Lithium Toxicity 11.4 Anxiety, Stress-Related & Obsessive-Compulsive Disorders 11.5 Alcohol Use Disorder & Withdrawal 11.6 Pharmacotherapy for Alcohol & Opioid Use Disorder 11.7 Toxidromes, Psychiatric Emergencies & Suicide Risk Assessment 11.8 Psychotic, Somatic Symptom, Factitious & Personality Disorders 11.9 Eating Disorders, Sleep Disorders & Sexual Health
13 Chapter 12: Dermatology (3% of Exam)
12.1 Dermatitis, Papulosquamous & Inflammatory Dermatoses 12.2 Acne, Rosacea & Cutaneous Infections 12.3 Herpes Zoster & Autoimmune Blistering Diseases 12.4 Nodules, Tumors & Cutaneous Oncology 12.5 Dermatologic Emergencies & Severe Cutaneous Adverse Reactions 12.6 Pigment Disorders, Alopecia, Nail Disease & Photosensitivity 12.7 Vascular Dermatoses, Environmental Injury & Cutaneous Signs of Systemic Disease
14 Chapter 13: Obstetrics & Gynecology / Women's Health (3% of Exam)
13.1 Contraception, Preconception Care & Teratogenicity 13.2 Hypertensive Disorders of Pregnancy & Gestational Diabetes 13.3 Thyroid Disease & Venous Thromboembolism in Pregnancy 13.4 Menopause & Menopausal Hormone Therapy 13.5 Abnormal Uterine Bleeding, Endometrial Disease & Gynecologic Cancer Screening 13.6 Breast Disorders & Diseases of the Vulva and Vagina 13.7 Menstrual Disorders, Fibroids, Endometriosis & Early Pregnancy Complications
15 Chapter 14: Geriatric Syndromes (3% of Exam)
14.1 Comprehensive Geriatric Assessment & Frailty 14.2 Falls, Gait Assessment & Polypharmacy 14.3 Urinary Incontinence & Pressure Injuries in Older Adults 14.4 Mild Cognitive Impairment, Dementia & Its Subtypes 14.5 Delirium & the Pharmacotherapy of Cognitive Disorders 14.6 Palliative Care, Hospice & Advance Care Planning 14.7 Chronic Wounds, Nutrition, Swallowing, Constipation & Hip Fracture 14.8 Sensory Impairment, Dizziness, Elder Mistreatment & Care Settings
16 Chapter 15: Allergy & Immunology (2% of Exam)
15.1 Anaphylaxis: Recognition & Emergency Management 15.2 Urticaria & Angioedema 15.3 Drug Allergy, Desensitization & Adult Immunodeficiency 15.4 Food Allergy, Insect Venom Hypersensitivity, Serum Sickness & Contrast Reactions 15.5 Rhinitis, Conjunctivitis, Eosinophilic & Mast Cell Disorders
17 Chapter 16: Preventive Medicine, Immunization & Clinical Epidemiology
16.1 The USPSTF Framework & Evidence-Based Cancer Screening 16.2 Cardiovascular & Metabolic Screening and Primary Prevention 16.3 Adult Immunization & Vaccines in Special Populations 16.4 Clinical Epidemiology, Biostatistics & Study Design
18 Chapter 17: Miscellaneous - Ethics, Patient Safety & Quality Improvement (2% of Exam)
17.1 Principles of Bioethics & Decisional Capacity 17.2 Informed Consent, Treatment Refusal & Special Scenarios 17.3 Surrogate Decision-Making, Advance Directives & Confidentiality 17.4 Patient Safety Science, Medical Error & Diagnostic Reasoning 17.5 Quality Improvement Methods, Health Disparities & Health Equity
19 Chapter 18: Perioperative Medicine & Medical Consultation
18.1 Preoperative Cardiovascular Risk Assessment 18.2 Preoperative Pulmonary Risk & Perioperative Medication Management 18.3 Perioperative Anticoagulation, Bridging & Postoperative Complications
20 Chapter 19: Ophthalmology (1% of Exam)
19.1 The Acute Red Eye & Ophthalmic Emergencies 19.2 Painless Vision Loss & Chronic Ophthalmic Disease 19.3 Uveitis, Scleritis & Orbital Disease
21 Chapter 20: Otolaryngology & Dental Medicine (1% of Exam)
20.1 Dizziness, Vertigo & Epistaxis 20.2 Ear Disorders, Hearing Loss & Upper Respiratory Infections 20.3 Oral Cavity, Salivary Gland, Laryngeal & Taste and Smell Disorders
13.3 Thyroid Disease & Venous Thromboembolism in Pregnancy
Key Takeaways Explain This Topic AI
Thyroid disease in pregnancy, peripartum or postpartum is a named topic under the thyroid blueprint subsection.
Levothyroxine requirements increase early in pregnancy, and known hypothyroid women should increase the dose as soon as pregnancy is confirmed.
Propylthiouracil is preferred in the first trimester and methimazole thereafter, because of differing teratogenic profiles.
Low-molecular-weight heparin is the anticoagulant of choice in pregnancy because warfarin is teratogenic and direct oral anticoagulants are not recommended.
Anticoagulation for pregnancy-associated venous thromboembolism continues through pregnancy and for at least six weeks postpartum.
Last updated: August 2026
- 1. Thyroid Disease in Pregnancy
- Gestational Thyroid Physiology
Pregnancy profoundly alters maternal thyroid physiology through two primary mechanisms:
Estrogen Stimulation: High circulating estrogen induces hepatic synthesis and glycosylation of Thyroid-Binding Globulin (TBG) while decreasing TBG clearance, resulting in a doubling of serum TBG levels. Consequently, Total T4 and Total T3 levels increase by ~50% (1.5x non-pregnant baseline), while free T4 and free T3 remain in the normal range.
hCG Cross-Reactivity: Human chorionic gonadotropin (hCG) shares an identical alpha subunit with TSH and exerts weak agonist activity on the thyroid follicular TSH receptor. Peak hCG levels at 10 to 12 weeks gestation stimulate thyroid hormone production, producing a transient physiologic suppression of serum TSH during the first trimester.
Trimester-Specific TSH Reference Ranges: First trimester TSH lower limit is ~0.1 mIU/L (upper limit ~2.5-3.0 mIU/L); second trimester 0.2-3.0 mIU/L; third trimester 0.3-3.0 mIU/L.
Hypothyroidism in Pregnancy
Clinical Significance: Maternal thyroxine is critical for fetal neurocognitive development, as the fetal thyroid gland does not produce endogenous thyroid hormone until 10 to 12 weeks of gestation . Untreated maternal hypothyroidism increases risks of miscarriage, preeclampsia, placental abruption, low birth weight, and impaired child neurodevelopment.
Management:
In patients with pre-existing overt hypothyroidism on Levothyroxine, the Levothyroxine dose must be increased by 25% to 30% immediately upon confirmation of pregnancy (e.g., instructing the patient to take two extra daily doses per week, or increasing the daily dose by 25-50 mcg).
Check serum TSH every 4 weeks through the first half of pregnancy (until 20 weeks) and at least once around 30 weeks gestation, titrating Levothyroxine to maintain TSH within trimester-specific reference ranges (<2.5 mIU/L).
Hyperthyroidism in Pregnancy
Etiology: Graves' disease accounts for >85% of cases. Must be distinguished from Gestational Transient Thyrotoxicosis (hCG-mediated hyperthyroidism associated with hyperemesis gravidarum, which is self-limiting and does not require antithyroid medications).
Pharmacotherapy Selection:
First Trimester: Propylthiouracil (PTU) is the drug of choice during the first trimester (weeks 1-12) because Methimazole is teratogenic during organogenesis, causing methimazole embryopathy (aplasia cutis congenita, choanal atresia, and tracheoesophageal fistula).
Second & Third Trimesters: Switch from PTU to Methimazole at the beginning of the second trimester (week 13-14) because PTU carries a significant risk of severe, fulminant drug-induced hepatotoxicity and acute liver failure.
Target: Maintain maternal Free T4 in the high-normal range using the lowest effective antithyroid dose to prevent iatrogenic fetal hypothyroidism and fetal goiter (since both PTU and Methimazole cross the placenta).
- 2. Venous Thromboembolism (VTE) in Pregnancy
- Hypercoagulability & Risk Profile
Pregnancy confers a 4- to 5-fold increased risk of VTE , which rises to a 20-fold increased risk in the first 6 weeks postpartum .
Pathophysiology represents all three elements of Virchow's triad: hypercoagulability (increased factors I, VII, VIII, IX, X, von Willebrand factor, and PAI-1; decreased protein S), venous stasis (gravid uterus compresses the inferior vena cava and left common iliac vein), and vascular endothelial injury during delivery.
80% of deep vein thromboses in pregnancy occur in the left lower extremity due to anatomic compression of the left common iliac vein by the crossing right common iliac artery and gravid uterus (May-Thurner anatomy).
Diagnostic Pathway
Suspected DVT:
Compression Duplex Ultrasonography of the proximal and distal lower extremity veins is first-line.
If initial ultrasound is negative but clinical suspicion is high (e.g., severe left leg/groin swelling suggesting iliac vein thrombosis), perform repeat compression ultrasound in 3 to 7 days or Magnetic Resonance Venography (MRV) of the pelvic/iliac veins.
Critical Pearl: Serum D-dimer is physiologically elevated in normal pregnancy and has a very high false-positive rate; a positive D-dimer cannot confirm VTE, and a negative D-dimer should not be relied upon to rule out VTE in pregnancy.
Suspected Pulmonary Embolism (PE):
First step: Obtain a Chest X-ray (CXR) .
If CXR is normal : Perform a Ventilation-Perfusion (V/Q) Scan . V/Q scan delivers lower radiation to maternal breast tissue than CTPA and negligible fetal radiation exposure.
If CXR is abnormal (infiltrate, atelectasis, effusion) or V/Q scan is unavailable/indeterminate: Perform Computed Tomography Pulmonary Angiography (CTPA) (with abdominal lead shielding; fetal radiation is minimal at <0.1 mGy, well below the 50 mGy teratogenic threshold).
Anticoagulation Management & Peripartum Timing
Anticoagulant of Choice: Low-Molecular-Weight Heparin (LMWH) (e.g., Enoxaparin 1 mg/kg SC every 12 hours for therapeutic anticoagulation; or 40 mg SC daily for thromboprophylaxis).
LMWH does not cross the placenta and does not cause fetal bleeding or teratogenicity.
Anti-Xa level monitoring is not routinely required for all patients, but is recommended in patients with renal impairment (eGFR <30 mL/min), extremes of body weight (<50 kg or >100 kg), or recurrent thrombosis. Peak anti-Xa target is 0.6 to 1.0 IU/mL (drawn 4 hours post-dose for twice-daily dosing).
Neuraxial Anesthesia (Spinal/Epidural) Timing Rules:
Therapeutic LMWH: Must be held for at least 24 hours prior to placement of neuraxial anesthesia or scheduled induction/cesarean delivery to prevent catastrophic spinal/epidural hematoma.
Prophylactic LMWH: Must be held for at least 12 hours prior to neuraxial blockade.
Transitioning near term: Many centers switch patients on therapeutic LMWH to intravenous Unfractionated Heparin (UFH) at 36 weeks gestation; UFH can be stopped 4 to 6 hours prior to delivery and is rapidly reversible with IV Protamine Sulfate.
Postpartum Anticoagulation: Resume anticoagulation 6 to 12 hours after uncomplicated vaginal delivery (12 to 24 hours after cesarean delivery) and continue for a minimum of 6 weeks postpartum and at least 3 months total therapy.
Contraindicated Anticoagulants in Pregnancy:
Warfarin: Teratogenic (Warfarin embryopathy: nasal hypoplasia, chondrodysplasia punctata, microcephaly, optic atrophy, fetal hemorrhage). Strictly contraindicated except in high-risk mechanical heart valves where low-dose warfarin (<5 mg/day) may be continued after specialist counseling.
Direct Oral Anticoagulants (DOACs: Apixaban, Rivaroxaban, Dabigatran): Cross the placenta with unknown fetal toxicity; contraindicated in pregnancy and during breastfeeding.