(a) Purpose. In the assessment and evaluation of the toxic characteristics of a chemical, determination of the potential developmental toxicity is important. The developmental toxicity study is designed to provide information on the potential hazard to the unborn which may arise from exposure of the mother during pregnancy.
(b) Definitions.
(1) Developmental toxicity is the property of a chemical that causes in utero death, structural or functional abnormalities or growth retardation during the period of development.
(2) Dose is the amount of test substance administered. Dose is expressed as weight of test substance (g, mg) per unit weight of a test animal (e.g., mg/kg).
(3) No-observed-effect level is the maximum concentration in a test which produces no observed adverse effects. A no-observed-effect level is expressed in terms of weight of test substance given daily per unit weight of test animal (mg/kg)
(c) Principle of the test method. The test substance is administered in graduated doses for at least part of the pregnancy covering the major period of organogenesis, to several groups of pregnant experimental animals, one dose level being used per group. Shortly before the expected date of delivery, the pregnant females are sacrificed, the uteri removed, and the contents examined for embryonic or fetal deaths, and live fetuses.
(d) Limit test. If a test at an exposure of at least 1000 mg/kg body weight, using the procedures described for this study, produces no observable developmental toxicity, then a full study using three dose levels might not be necessary.
(e) Test procedures -
(1) Animal selection -
(i) Species and strain. Testing shall be performed in at least 2 mammalian species. Commonly used species include the rat, mouse, rabbit, and hamster. If other mammalian species are used, the tester shall provide justification/reasoning for their selection. Commonly used laboratory strains shall be employed. The strain shall not have low fecundity and shall preferably be characterized for its sensitivity to developmental toxins.
(ii) Age. Young adult animals (nulliparous females) shall be used.
(iii) Sex. Pregnant female animals shall be used at each dose level.
(iv) Number of animals. At least 20 pregnant rats, mice or hamsters or 12 pregnant rabbits are required at each dose level. The objective is to ensure that sufficient pups are produced to permit meaningful evaluation of the potential developmental toxicity of the test substance.
(2) Control group. A concurrent control group shall be used. This group shall be an untreated or sham treated control group, or, if a vehicle is used in administering the test substance, a vehicle control group. Except for treatment with the test substance, animals in the control group(s) shall be handled in an identical manner to test group animals.
(3) Dose levels and dose selection.
(i) At least 3 dose levels with a control and, where appropriate, a vehicle control, shall be used.
(ii) The vehicle shall neither be developmentally toxic nor have effects on reproduction.
(iii) To select the appropriate dose levels, a pilot or trial study may be advisable. It is not always necessary to carry out a trial study in pregnant animals. Comparison of the results from a trial study in non-pregnant, and the main study in pregnant animals will demonstrate if the test substance is more toxic in pregnant animals. If a trial study is carried out in pregnant animals, the dose producing embryonic or fetal lethalities or maternal toxicity shall be determined.
(iv) Unless limited by the physical/chemical nature or biological properties of the substance, the highest dose level shall induce some overt maternal toxicity such as reduced body weight or body weight gain, but not more than 10 percent maternal deaths.
(v) The lowest dose level should not produce any grossly observable evidence of either maternal or developmental toxicity.
(vi) Ideally, the intermediate dose level(s) should produce minimal observable toxic effects. If more than one intermediate concentration is used, the concentration levels should be spaced to produce a gradation of toxic effects.
(4) Observation period. Day 0 in the test is the day on which a vaginal plug and/or sperm are observed. The dose period shall cover the period of major organogenesis. This may be taken as days 6 to 15 for rat and mouse, 6 to 14 for hamster, or 6 to 18 for rabbit.
(5) Administration of test substance. The test substance or vehicle is usually administered orally, by oral intubation unless the chemical or physical characteristics of the test substance or pattern of human exposure suggest a more appropriate route of administration. The test substance shall be administered approximately the same time each day.
(6) Exposure conditions. The female test animals are treated with the test substance daily throughout the appropriate treatment period. When given by gavage, the dose may be based on the weight of the females at the start of substance administration, or, alternatively, in view of the rapid weight gain which takes place during pregnancy, the animals may be weighed periodically and the dosage based on the most recent weight determination.
(7) Observation of animals.
(i) A gross examination shall be made at least once each day.
(ii) Additional observations shall be made daily with appropriate actions taken to minimize loss of animals to the study (e.g., necropsy or refrigeration of those animals found dead and isolation or sacrifice of weak or moribund animals).
(iii) Signs of toxicity shall be recorded as they are observed, including the time of onset, the degree and duration.
(iv) Cage-side observations shall include, but not be limited to: changes in skin and fur, eye and mucous membranes, as well as respiratory, autonomic and central nervous systems, somatomotor activity and behavioral pattern.
(v) Measurements should be made weekly of food consumption for all animals in the study.
(vi) Animals shall be weighed at least weekly.
(vii) Females showing signs of abortion or premature delivery shall be sacrificed and subjected to a thorough macroscopic examination.
(8) Gross necropsy.
(i) At the time of sacrifice or death during the study, the dam shall be examined macroscopically for any structural abnormalities or pathological changes which may have influenced the pregnancy.
(ii) Immediately after sacrifice or as soon as possible after death, the uterus shall be removed and the contents examined for embryonic or fetal deaths and the number of viable fetuses. The degree of resorption shall be described in order to help estimate the relative time of death of the conceptus. The weight of the gravid uterus should be recorded for dams that are sacrificed. Gravid uterine weights should not be obtained from dead animals if autolysis or decomposition has occurred.
(iii) The number of corpora lutea shall be determined for all species except mice.
(iv) The sex of the fetuses shall be determined and they shall be weighed individually, the weights recorded, and the mean fetal weight derived.
(v) Following removal, each fetus shall be examined externally.
(vi) For rats, mice and hamsters, one-third to one-half of each litter shall be prepared and examined for skeletal anomalies, and the remaining part of each litter shall be prepared and examined for soft tissue anomalies using appropriate methods.
(vii) For rabbits, each fetus shall be examined by careful dissection for visceral anomalies and then examined for skeletal anomalies.
(f) Data and reporting -
(1) Treatment of results. Data shall be summarized in tablular form, showing for each test group: the number of animals at the start of the test, the number of pregnant animals, the number and percentages of live fetuses and the number of fetuses with any soft tissue or skeletal abnormalities.
(2) Evaluation of results. The findings of a developmental toxicity study shall be evaluated in terms of the observed effects and the exposure levels producing effects. It is necessary to consider the historical developmental toxicity data on the species/strain tested. A properly conducted developmental toxicity study should provide a satisfactory estimation of a no-effect level.
(3) Test report. In addition to the reporting requirements as specified under 40 CFR part 792, subpart J the following specific information shall be reported:
(i) Toxic response data by concentration.
(ii) Species and strain.
(iii) Date of death during the study or whether animals survived to termination.
(iv) Date of onset and duration of each abnormal sign and its subsequent course.
(v) Food, body weight and uterine weight data.
(vi) Pregnancy and litter data.
(vii) Fetal data (live/dead, sex, soft tissue and skeletal defects, resorptions).
(g) References. For additional background information on this test guideline the following references should be consulted:
(1) Department of Health and Welfare. The Testing of Chemicals for Carcinogenicity, mutagenicity and Teratogenicity. Minister of Health and Welfare (Canada: Department of Health and Welfare, 1975).
(2) National Academy of Sciences. “Principles and Procedures for Evaluating the Toxicity of Household Substances.” A report prepared by the Committee for the Revision of NAS Publication 1138, under the auspices of the Committee on Toxicology, National Research Council, National Academy of Sciences, Washington, DC (1977).
(3) World Health Organization. Principles for the Testing of Drugs for Teratogenicity. WHO Technical Report Series No. 364. (Geneva: World Health Organization, (1967).
[50 FR 39397, Sept. 27, 1985, as amended at 52 FR 19077, May 20, 1987]