ABT Reproductive and Developmental Toxicology 1 — Questions and Answers
Question 1: Which period of prenatal development is most sensitive to teratogenic agents causing structural malformations?
- Weeks 1–2 (pre-implantation)
- Weeks 3–8 (organogenesis) (Correct answer)
- Weeks 9–38 (fetal period)
- Week 40 (peripartum)
Correct answer: Weeks 3–8 (organogenesis)
The embryonic period (weeks 3–8), when organogenesis occurs, is the most sensitive window for structural teratogenesis because organ rudiments are being established.
Question 2: Thalidomide caused phocomelia (limb reduction defects) when taken during which gestational window?
- Days 1–14
- Days 27–40 (Correct answer)
- Weeks 12–20
- Third trimester
Correct answer: Days 27–40
Thalidomide causes limb reduction defects (phocomelia) when exposure occurs during days 27–40 of gestation, coinciding with limb bud development.
Question 3: The Reproductive and Developmental Toxicant classification system in the US uses which regulatory framework?
- REACH (EU)
- Prop 65 / California Safe Drinking Water Act
- EPA Developmental Neurotoxicity Guidelines (DNT)
- GHS/OSHA Hazard Communication Standard (Correct answer)
Correct answer: GHS/OSHA Hazard Communication Standard
The GHS (Globally Harmonized System) adopted by OSHA's Hazard Communication Standard classifies reproductive and developmental toxicants into Category 1A, 1B, and 2 based on evidence strength.
Question 4: Which drug is a known human teratogen classified FDA Category X and causes fetal hydantoin syndrome?
- Valproic acid
- Phenytoin (Correct answer)
- Carbamazepine
- Lithium
Correct answer: Phenytoin
Phenytoin causes fetal hydantoin syndrome, characterized by craniofacial abnormalities, digit/nail hypoplasia, and cognitive impairment, and is classified FDA Category X (contraindicated in pregnancy).
Question 5: Which mechanism explains the selective vulnerability of the fetal brain to methylmercury neurotoxicity?
- Immature liver conjugation of mercury
- Incomplete blood-brain barrier and active neuronal migration in the developing CNS (Correct answer)
- Higher renal clearance of mercury in fetuses
- Greater mercury intake via amniotic fluid
Correct answer: Incomplete blood-brain barrier and active neuronal migration in the developing CNS
The immature blood-brain barrier and ongoing neuronal migration, proliferation, and differentiation during fetal development make the fetal CNS highly vulnerable to methylmercury neurotoxicity.
Question 6: Which endocrine-disrupting chemical is associated with clear cell adenocarcinoma of the vagina in daughters of women treated during pregnancy?
- Bisphenol A (BPA)
- DDT
- Diethylstilbestrol (DES) (Correct answer)
- Atrazine
Correct answer: Diethylstilbestrol (DES)
DES (diethylstilbestrol), a synthetic estrogen prescribed from the 1940s–1970s, caused transplacental carcinogenesis resulting in vaginal clear cell adenocarcinoma in DES daughters.
