636 Obstetrics and Gynecology Board Review •••
❍ What are the adverse reproductive outcomes associated with occupational and environmental exposure?
These include infertility, single gene defects, chromosome abnormalities, spontaneous abortions, congenital
malformation, IUGR, perinatal deaths, developmental disabilities, behavioral disorders, and malignancies.
❍ What is “recall bias” in reproductive toxicology?
Women with an adverse pregnancy outcome such as spontaneous abortion, fetal or neonatal demise, or a
congenital malformation are more likely to recall exposure to environmental or occupational or infectious agents.
However, those with satisfactory pregnancy outcomes tend to forget such exposures.
❍ What is “selection bias” in reproductive toxicology?
When studying a particular outcome or teratogenic agent, there are potential problems that can affect the
interpretation of reported results. Some examples include (i) inaccurate or incomplete information about single
or multiple exposures and confounding exposures, (ii) incomplete, inaccurate or absent survey responses, (iii) not
validating the reproductive history, (iv) recall bias, (v) inaccurate methods of data collection, and (vi) investigators’
bias toward one of the possible outcomes of a study.
❍ Who is more susceptible to carbon monoxide (CO) poisoning, a mother or her fetus?
The fetus. CO causes toxicity by asphyxiation. It binds to hemoglobin to form carboxyhemoglobin (COHb).
Fetal COHb levels tend to be 10–15% higher than maternal levels. If a woman has a significant enough exposure
to cause unconsciousness, >50% of fetuses will die in utero and the many of the remainder suffer from significant
impairment.
❍ How do you treat a patient with suspected CO poisoning?
High-dose O 2 displaces CO from Hb and causes it to diffuse out of tissues. Hyperbaric oxygen therapy will
more significantly reduce the half-life of CO in the bloodstream and it is the treatment of choice when available.
The half-life of CO in maternal blood is approximately 230 minutes and it is longer in the fetus. The half-life is
reduced to 90 minutes with 100% and can be safely reduced to <30 minutes with hyperbaric oxygen therapy.
❍ What maternal blood level of lead is toxic to her fetus?
Maternal blood lead levels as low as 10 mg/mL have been linked to neurobehavioral disturbances in their offspring.
The CDC has defined blood levels above 25 mg/mL as elevated, because this is when toxic effects are seen in adults,
but the fetus appears to be more susceptible to lead poisoning.
❍ What effect does lead have on the human body?
Lead can affect multiple organ systems and may cause death in adults when blood concentrations exceed 300 mg/mL.
The central nervous system, GI tract, kidneys, joints, and reproductive systems may all be affected. Studies vary
whether lead causes structural malformations in exposed fetuses, but it is clear that lead causes learning disabilities
and other behavioral disturbances.
❍ Which women today are most at risk of mercury poisoning?
Fish-eaters. The only real human exposure to organic mercury is through consumption of fish. Fetuses are more
susceptible to toxic effects of mercury than their maternal hosts, so extra care must be taken when working
with pregnant patients. Large exposures to methyl mercury have resulted in infants with microcephaly, mental
retardation, cerebral palsy, and blindness.