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Birth defects among the children of atomic-bomb survivors (1948-1954)

No statistically significant increase in major birth defects or other untoward pregnancy outcomes was seen among children of survivors. Monitoring of nearly all pregnancies in Hiroshima and Nagasaki began in 1948 and continued for six years. During that period, 76,626 newborn infants were examined by ABCC physicians. When surveillance began, certain dietary staples were rationed in Japan, but ration regulations made special provision for women who were at least 20 weeks pregnant. This supplementary ration registration process enabled the identification of more than 90% of all pregnancies and the subsequent examination of birth outcomes.

Physical examination of newborns during the first two weeks after birth provided information on birth weight, prematurity, sex ratio, neonatal deaths, and major birth defects. Newborn frequencies of untoward pregnancy outcomes, stillbirths, and malformations are shown in Tables 1, 2, and 3 according to parental dose or exposure. The incidence of major birth defects (594 cases or 0.91%) among the 65,431 registered pregnancy terminations for which parents were not biologically related accords well with a large series of contemporary Japanese births at the Tokyo Red Cross Maternity Hospital, where radiation exposure was not involved and overall malformation frequency was 0.92%. No untoward outcome showed any relation to parental radiation dose or exposure.

The most common defects seen at birth were anencephaly, cleft palate, cleft lip with or without cleft palate, club foot, polydactyly (additional finger or toe), and syndactyly (fusion of two or more fingers or toes). These abnormalities accounted for 445 of the 594 (75%) malformed infants in Table 3.

Since many birth defects, especially congenital heart disease, are not detected in the neonatal period, repeat examinations were conducted at age eight to ten months. Among the 18,876 children re-examined at that age, 378 had one or more major birth defect (2.00%), compared with 0.97% within two weeks of birth. Again, there was no evidence of relationships to radiation dose.

Table 1. Untoward pregnancy outcomes (stillbirths, malformations, and neonatal deaths within two weeks of birth) among A-bomb survivors, by parental radiation doses and cases/children examined, 1948-1953
Mother's weighted dose (Gy)
Father's weighted dose (Gy)
<0.01 0.01-0.49
≥0.50
<0.01
2,257/45,234
(5.0%)
81/1,614
(5.0%)
29/506
(5.7%)
0.01-0.49
260/5,445
(4.8%)
54/1,171
(4.6%)
6/133
(4.5%)
≥0.50
63/1,039
(6.1%)
3/73
(4.1%)
7/88
(8.0%)

Table 2. Stillbirths to A-bomb survivors by cases/children examined, 1948-1953
Mother's exposure
conditions
Father's exposure condition
Not in cities Low to middle doses
High dose
Not in cities
408/31,559
(1.3%)
72/4,455
(1.6%)
9/528
(1.7%)
Low to middle doses
279/17,452
(1.6%)
139/7,881
(1.8%)
13/608
(2.1%)
High doses
26/1,656
(1.6%)
6/457
(1.3%)
2/144
(1.4%)

Table 3. Malformations diagnosed within two weeks of birth by
cases/children examined, 1948-1953
Mother's exposure
conditions
Father's exposure conditions
Not in cities Low to middle doses
High doses
Not in cities
294/31,904
(0.92%)
40/4,509
(0.89%)
6/534
(1.1%)
Low to middle doses
144/17,616
(0.82%)
79/7,970
(0.99%)
5/614
(0.81%)
High doses
19/1,676
(1.1%)
6/463
(1.3%)
1/145
(0.7%)

In addition, a clinical health study of about 12,000 individuals was conducted between 2002 and 2006 with a focus on lifestyle diseases, based on the idea that adulthood is when disorders from radiation effects may develop. In this study, possible relationships between parental exposure and a combination of six multifactorial diseases (e.g., diabetes and hypertension) were analyzed, taking into consideration such lifestyle habits as drinking and smoking. The results showed no evidence at this time of increased risk of these multifactorial diseases among the target individuals. However, given that the subjects were still young at the time of the health examinations, with an average age of 48.6, it would be desirable to continue the clinical health study of this fixed cohort.
References about this subject
Neel JV, Schull WJ, eds. The Children of Atomic-bomb Survivors: A Genetic Study. Washington DC: National Academy Press; 1991
Nakamura N: Genetic effects of radiation in atomic-bomb survivors and their children: Past, present and future. Journal of Radiation Research (Tokyo) 2006; 47(Suppl):B67-73
Otake M, Schull WJ, Neel JV: Congenital malformations, stillbirths, and early mortality among children of atomic bomb survivors: A reanalysis. Radiation Research 1990; 122:1-11
Fujiwara S, Suyama A, Cologne JB, Akahoshi M, Yamada M, Suzuki G, Koyama K, Takahashi N, Kasagi F, Grant EJ, Lagarde F, Hsu WL, Furukawa K, Ohishi W, Tatsukawa Y, Neriishi K, Takahashi I, Ashizawa K, Hida A, Imaizumi M, Nagano J, Cullings HM, Katayama H, Ross NP, Kodama K, Shore RE. Prevalence of adult-onset multifactorial disease among offspring of atomic bomb survivors. Radiation Research 2008; 170:451-7