Summary
Drug use during pregnancy requires careful risk–benefit assessment. Maternal, fetal, and placental pharmacokinetics determine drug exposure. Risk depends on fetal age, with organogenesis being most critical. FDA pregnancy categories and knowledge of drug-specific teratogenicity guide clinical decision-making. Non-essential drugs, smoking, alcohol, and certain supplements should be avoided to optimize fetal outcomes.
Epidemiology
Over 50% of pregnant women are exposed to prescribed, over-the-counter (OTC), social, or illicit drugs during pregnancy. Drugs should generally be avoided unless absolutely necessary, as approximately 2–3% of all birth defects are drug-related.
Pharmacokinetics During Pregnancy
Maternal Changes
-
Increased body fluid volume
-
Altered cardiovascular and pulmonary function
-
Gastric activity modifications
-
Changes in serum binding proteins and their occupancy
-
Renal function alterations
Fetal Pharmacokinetics
-
Fetal plasma proteins differ from maternal proteins
-
Placental drug transfer undergoes first-pass metabolism in the fetal liver
-
Liver and kidney functions are immature, affecting drug clearance
Placental Pharmacokinetics
-
Increased placental blood flow during gestation
-
Drug transfer influenced by placental blood flow, surface area, and metabolism
-
At term, nearly all compounds can reach the fetus
Drug Transfer Determinants
-
Molecular weight: <500 D crosses easily; <1000 D crosses partially
-
Lipid solubility, protein binding, degree of ionization
-
Maternal blood concentration is the main determinant
-
Similar principles govern drug passage into breast milk; weak bases may be trapped due to ion trapping
Fetal Vulnerability by Gestational Age
|
Stage |
Days |
Risk Type |
|
Pre-implantation |
0–20 |
All-or-nothing effect; teratogenesis unlikely |
|
Organogenesis |
20–56 |
Highest risk; structural malformations, spontaneous abortion |
|
Post-organogenesis |
2nd–3rd trimester |
Functional defects; altered growth or organ function |
Types of Drug Effects
-
Teratogenicity: Detected at birth (e.g., thalidomide)
-
Long-term latency: Effects manifest later (e.g., DES, testicular dysfunction)
-
Predisposition to metabolic disease: Low birth weight associated with adult diabetes, hypertension, heart disease
- Neurodevelopmental impairment: E.g., phenobarbital exposure
FDA Pregnancy Risk Categories
|
Category |
Description |
|
A |
Human studies show no risk |
|
B |
Animal studies show no risk; human studies lacking |
|
C |
Animal studies show adverse effects; human studies lacking |
|
D |
Evidence of fetal risk; benefits may outweigh risks |
|
X |
Contraindicated; risk outweighs benefits |
Common Drugs and Safety in Pregnancy
Antibiotics:
|
Category |
Drugs |
Notes |
|
B |
Penicillins, Cephalosporins, Macrolides, Nitrofurantoin (except late pregnancy), Metronidazole (avoid lactation), Vancomycin (oral) |
Safe in pregnancy, select with caution |
|
C |
Aminoglycosides (neomycin-tobramycin), Quinolones, Trimethoprim, Chloramphenicol |
Potential fetal harm; use only if necessary |
|
D |
Tetracyclines, Aminoglycosides (streptomycin-gentamicin) |
Teratogenic: teeth discoloration, hearing loss |
Antivirals:
|
Category |
Drugs |
Notes |
|
B |
Acyclovir, Valacyclovir |
Safe for herpes, especially 2nd–3rd trimesters |
|
C |
Amantadine, Lamivudine, Delaviridine, Indinavir |
Potential teratogenicity; use if alternatives unavailable |
|
Avoid |
Efavirenz, Ribavirin, Interferon α combinations |
Neural tube defects, preterm birth, hepatotoxicity |
Antifungals:
|
Category |
Drugs |
Notes |
|
B |
Amphotericin B, Terbinafine |
Preferred systemic agents |
|
C |
Ketoconazole |
Teratogenic effects possible |
|
C/D |
Fluconazole |
Dose-dependent teratogenicity |
|
X |
Griseofulvin |
Contraindicated |
Antihypertensives:
|
Category |
Drugs |
Notes |
|
B/C |
Methyldopa, Labetalol, Hydralazine, Nifedipineز |
Safe first-line therapy |
|
Avoid |
ACE inhibitors, ARBs, Atenolol, Thiazides |
Fetal hypotension, renal failure, growth restriction |
Anticoagulants:
|
Drug |
Notes |
|
Heparin |
Preferred; does not cross placenta |
|
Warfarin |
Category X/D; teratogenic, fetal hemorrhage risk |
Analgesics:
-
Acetaminophen: Safe
-
NSAIDs: Avoid after 30 weeks (ductus arteriosus closure)
-
Opioids: Caution; neonatal withdrawal possible
Antiepileptics:
-
Phenytoin, Carbamazepine: D, fetal hydantoin syndrome
-
Valproate: D, neural tube defects, cognitive impairment
Other Notable Drugs:
|
Drug |
Risk |
|
Thalidomide |
X, phocomelia, heart and eye defects |
|
Methotrexate |
X, major congenital anomalies |
|
Isotretinoin |
X, severe birth defects |
|
Lithium |
D, Ebstein anomaly |
|
SSRIs |
C/D, small increased risk of heart defects, neonatal withdrawal |
Lifestyle Considerations
-
Smoking: Hypoxia, growth restriction, congenital defects, childhood asthma
-
Alcohol: Low birth weight, fetal alcohol syndrome, neurodevelopmental deficits
-
Caffeine: Safe in moderate amounts (<1 cup/day)
- Aspartame: Safe in moderate intake (<1 liter/day)
احصل على التجربة الكاملة
اشترك للوصول لفيديوهات الشرح التفصيلي والبطاقات التعليمية التفاعلية وأسئلة الممارسة مع تتبع التقدم.