ML20133D591
| ML20133D591 | |
| Person / Time | |
|---|---|
| Site: | Three Mile Island  |
| Issue date: | 09/02/1984 |
| From: | Bratz J, James Kim, Tokuhata G PENNSYLVANIA, COMMONWEALTH OF |
| To: | |
| Shared Package | |
| ML20132B167 | List: |
| References | |
| FOIA-85-285 NUDOCS 8507220244 | |
| Download: ML20133D591 (9) | |
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THREE MILE ISLAND (THI) NUCLEAR ACCIDENT AND PREGNANCY OUTCOME
- 1 George K. Tokuhata, Dr.P.H. , Ph.D.**
Joyce Kim, Ed.D.
. Jane Bratz, B.S.S.
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Division of Epidemiology Research Pennsylvania Department of Health
- 0ral presentation at the XIIth International Biometric Conference, September 2 - 7, 1984
- Dr. Tokuhata is Division Director. He is also Professor of Epidemiology and Biostatistics, Graduate School of Public Health, University of Pittsburgh, t
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THREE MILE ISLAND (TMI) NUCLEAR ACCIDENT AND PREGNANCY OUTCOME The Three ' tile. Island (TMI) nuclear accident of March 28, 1979 created ~
marked social unrest locally, nationally, and internationally, particularly with respect to the health and safety aspects of nuclear energy. Subsequent to the TMI accident, the Pennsylvania Department of Health initiated a compre-hensive epidemiologic evaluation of possible health effects upon local popula-tion of uncontrolled radiation releases from the damaged nuclear reactor and of severe psychological disturbance caused by fears and anxieties about radia-tion exposure.
One of the most important studies developed shortly after the accident was to determine if the TMI nuclear accident has had any measurable impacts upon pregnancy outcome within a 10-mile area. The embryo and the fetus are highly
' sensitive to both ionizing radiation and maternal stress, depending upon the severity' of such environmental insults, the mode of exposure, and the gestational age at exposure. This study covered a cohort of 3,529 single deliveries which took place from March 28, 1979 through March 27, 1980 representing mothers and fetuses exposed to radiation and subjected to psycholoaical stress durina and shortly after the accident. In contrast, the control cohort of 3,624 single daliveries which took place one year later from March 28, 1980 through March 27, 1981 represented mothers and fetuses living in the same 10-mile area communities, but not directly exposed to the accident radiation.
Measures of adverse pregnancy outcome investigated were: fetal deaths
'(stillbirths and abortions after 16 week gestation), neonatal death (within 28 days of delivery), prematurity (gestation less than 37 weeks), low birthweicht (2,500 grams or less), connenital anomalies (major or minor defects recognized at birth), and low Apoar scores (less than 7 at one minute postpartum). Many -
factors other than radiation and stress are known to influence the course of pregnancy and fetal growth; thus, detailed data on such factors were collected, including maternal characteristics (sociodemographic and behavioral attributes and medical-obstetric histories), health care provider characteristics, and nature of prenatal care provided. These confounding factors were converted into 34 discrete variables for statistical analyses.
Maternal stress during and shortly after the TMI accident was estimated by overt personal statements of " anxiety / fear" as reported by individual preg-nant women, and by actual stress-coping patterns described, such as taking extra medications (tranquilizers, sleeping pills, analgesics, cardiac or hypertensive preparations) and/or smoking / drinking more than usual amounts because of their anxiety and fear.
Maternal / fetal radiation _ exposure during the 10-day crisis was estimated.
For thisyrpose, already documented thermoluminescent do.simetry (TLD) and other source data including time-dependent dose-rate distribution compiled by govern-
. ment and non-government agencies were used to estimate both maximum possible and likely doses to each individual pregnant woman and the fetus. In addition to whole body gamma and thyroid doses to the mother and the fetus, combined gamma and beta doses to the skin were also estimated. Shielding factors related to building or clothing were not taken into account in dose calculation.
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In order to assess possible health effects of TMI radiation and the related stress upon pregnancy outcome, it was necessary to take into account the influences
.of all 34 confounding variables under study. Since these confounding variables and all of the dependent variables were dichotomized, multivariate logistic regression analysis was used when each of the six pregnancy outcome measures was evaluated in relation to TMI radiation and TMI stress.
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After simultaneous adjusting for the influences of those confounding variables described earlier, the incidences of fetal and neonatal mortalities, congenital anomalies, prematurity, low birthweight, and low Apgar scores within the exposed study cohort were not significantly different from those within the .
unexposed control cohort. This suggests that the impact of the TMI nuclear accident upon pregnancy outcome was negligible, if any.
A further analysis of the comprehensive data by the multivariate logistic regression method indicated that neither radiation exposure nor maternal psycho-logical stress as such was significantly correlated to the incidence of fetal-neonatal mortalities, congenital anomalies, prematurity, low birthweight, or low Apgar scores within the exposed study cohort.
However, excess medication taken by those pregnant women who were severely stressed during and shortly after the accident was significantly correlated to the incidence of low Apgar' scores measured at one minute postpartum, and to the incidence of low birthweight. This was interpreted 'to mean that, other factors being equal, one-minute Apgar scores among newborn infants were significantly influenced by maternal excess medications through the accident-caused stress and anxiety. Our data also showed that the Apgar scores at 5 minutes postpartum were not significantly correlated to the same maternal excess medications while pregnant. It appears that the effect on the Apgar scores was only short-lived and, thus, would probably have a minimum clinical significance. On the other hand, the significant relationship found between excess medications mediated via stress and anxiety and the incidence of low birthweight is of potential epidemio-logic importance. This is particularly so in view of the fact that low birthweight is known to be the single most important prognostic indicator in child growth and development.
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Because of the differential sensitivity of the fetus by gestational ages when exposed to environmental insults, further analysis was conducted according to the trimester of gestation at the time of the TMI accident. On the average, there were approximately 850 women in each trimester group. For each pregnant woman the last date of menstrual period (LMP) or the time of conception was determined. The incidence of low Apgar scores at one minute was the hiahest
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within the first trimester group (10; per 1,000 births). Furthermore, this was the only trimester group in which there was a significant association between excess medications and low Apgar scores as indicated by both x2 and 0 tests.
Having observed that such significant association exists only among women in the early gestation period, it was of further interest to determine which of the first three months is more important in terms of potential influence by excess medications. According to our data, it was the second-month gestation group thauustained the significant association. -
A similar analysis was conducted with respect to the effect of excess medications upon low birthweight. A significant association between excess medications and low birthweight was found only within the third trimester and zero trimester groups as indicated by both x2 and 0 tests. The zero trimester group represents those women who became pregnant within three months subsequent to the accident when the level of psychological stress remained high.
Further analysis showed that the significant association observed earlier did not appear consistently for the entire third trimester group, but was shown only among those women who were in the 8th-month aestation. Likewise, within the zero trimester group, a significant association was observed only among those women who became pregnant during the third month (June 1979) following the TMI accident.
Interpretation of these interesting observations may not be self-evident, but is not difficult to speculate. Effects of certain drugs and medications
taken by pregnant women upon fetus have been reported previously. We have identified what categories of medications taken in excess frequency or amount .
are'important, what gestational ages are important when excess medications can, have negative effects, and what kinds of effects in terms of pregnancy outcome may result. According to our study, fetal and neonatal mortalities, congenital 1
anomalies or premature births were not affected by excess medications while pregnant.
Radiation exposure to pregnant women can cause a variety of damages to the embryo and the fetus including death or rejection from the womb. However, radiation levels below 10 rem have not shown this association either because it does not exist at these low levels or because it is too small to measure with the existing epidemiologic method. According to the radiation doses estimated by the Department of Radiation Health, University of Pittsburgh, pregnant women living within 10 miles of the TMI plant and their fetuses received an average "likely" full-body gamma dose of 4 millirem and an average " maximum" full-body gamma dose of 10 millirem during the 10-day crisis.
From such low doses, no radiation health effects from the TMI accident would be detectable including spontaneous abortions. Nevertheless, confusion, uncertainty and public apprehension continued because cf their own perceived exposure to much larger doses of radiation. Furthermore, official government reports on radiation releases have been challenged by some radiation scientists.
For this reason, it is prudent to consider possible radiation effect upon spon-taneous abortions. On the other hand, maternal stress is also known to be capable of causing spontaaeous abortions; thus it must also be considered independently.
In order to determine whether the incidence of spontaneous abortion was greater than expected near the TMI nuclear power plant durino the months follow-ing the accident, all pregnant women living within the 5-mile radius and included
o s in the special census conducted in June 1979 were recontacted one year later and pregnancy outcome status verified. Using the life table method, it was found, given pregnancies after four completed weeks of gestation, that the estimated incidence of spontaneous abortion (miscarriage before completion of 16 week gestation) was 15.1 percent. Combining spontaneous abortions and still-births (delivery of a dead fetus after 16 week gestation),theestimatedincidence was 16.1 percent. Both incidences are comparable to baseline studies of fetal loss. This indicates that the effects of the TMI accident upon spontaneous abortion was negligible, if any.
Potential biological effects of ionizing radiation can also be shown in terms of sex ratio among newborn infants. Theoretically, when paternal gonads were irradiated significantly, relatively fewer boy babies than usual may be born because of a decreased viability of the germ cells carrying Y chromosome.
In view of-the public perception of high doses of radiation exposure during the TMI nuclear accident, sex ratio of newborn infants was compared between the
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10-mile area around TMI and the State of Pennsylvania as a whole. Sex ratios (number of boys per 100 girls) for the entire State as compared with the TMI area were 105.3 vs.103.2 during 1977,105.3 vs.105.1 during 1978, 104.8 vs.
103.7 during 1979, and 104.8 vs. 105.8 during 1980. These minor changes / differ-ences were all within a range of random variations.
Radiation releases during the accident at the TMI nuclear plant included radioactive iodine which can be taken up by the fetal thyroid gland after 10 week gestation. It is also known that the fetal thyroid gland is much more sensitive to radioactive iodine than is the mother's thyroid gland. Because i
of this biological affinity and differential sensitivity, a special study was conducted to determine if the incidence of hypothyroidism among newborn infants waselevatedin[the10-mileTMI area follnwino the accident. ' The
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t 0 statewide screening program for congenital hypothyroidism which started in mid-1978 in Pennsylvania provided the necessary data.
During the March 28, 1979 - March 27, 1980 period, only one case of con-genital hypothyroidism was identified within the 10-mile study area among ~
approximately 4,000 newborn infants. This incidence rate was well within a normal range of expectation.
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Meteorological records indicated that during the first 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> followinc the accident when most of the radioactive releases took place, the prevailing wind direction was north and northwest, which generally determined the radio-active plume pathways. Therefore, the incidence of thyroid abnonnalities, if any, would have been higher in the down-wind areas. After March 28 through December 31, 1979, no single case of congenital hypothyroidism was reported in any of the eight adjacent counties located north and northwest from the TMI plant.
However, a total of seven cases of congenital hypothyroidism were reported during 1979 within one particular county, Lancaster, located some 30 miles south-east of TMI. Because of physical proximity and timing of tnese reported cases, a special epidemiologic investigation was conducted to determine if these cases were etiologically related to the TMI accident. The results of this investigation revealed that (a) one of the seven cases was diagnosed in January (prior to the TMI accident); (b) one infant with multiple central nervous system anomalies was born three months after the accident, thus such anomalies are most likely to have already been developed at the time of the accident; (c) one case was of dysgensis, representing one of discordant Amish twins, thus, non-supportive of the etiology secondary to radiation exposure; (d) another case of dysgenesis in whom the thyroid glands were displaced from the normal position, thus, non-functioning; (e) one case of dyshormonogenesis from an Amish family where the condition (lack of enzyme to synthesize thyroxine) was inherited from the parents; and (f) for the remaining '
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- two cases diagnostic thyroid scan was not conducted. From these epidemiologic observations along with the extremely low levels of radioactive iodine detected in cow's milk in the area, it was concluded that these reported cases of hypo-thyroidism in _Lancaster were not directly related to the TMI accident. It should be noted that Lancaster has a large Amish population known to have relatively more than usual number of birth defects due mainly to consanguinity.
The accidental radiation received by people residing in the vicinity of TMI came almost entirely from xenon gases and traces of radiciodine, all of which have very short half-life. Based on the available data and calculations, the maximum cumulative whole-body ganna dose to anyone off site was estimated to be no more than 100 mrem within 10 miles of the plant. Additional exposure to the population came from the beta radiation dose to the skin and from the inhalation dose to the lung. The total dose to the skin could have been much larger th Ag_the whole-body gamma dose by a . factor of.3 to. 4 if the protective effects of shelter and clothing were disregarded.
Low dose radiation exposure at the level no more than natural background radiation in the TMI area is not expected to produce any detectable health consequences among local population. This expectation has been consiste.nt with the results of our various studies 'on pregnancy outcome as reported in this paper. However, since the level of government-reported radiation doses has been challenged by some nuclear scientists, and because the potential chronic effects of psychological stress and related behavioral disorders are largely unknown at this time, it is prudent to continue health surveillance over the accident-exposed people including those in-utero exposed children and their mothers as well as general population. The Pennsylvania Department of Health has established two long-term followup registries including general population and a cohort of mothers and children which are being pursued for periodic epidem-iologic assessment.
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