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Chapter IX ANALYSIS OF THE STILLBIRTH DATA 9.1 The trait. The definition of a stillbirth employed in this study is an infant who shows no signs of life at birth, following a period of gestation of at least 20 weeks. Any infant that moves, makes respiratory attempts, or is born with a beating heart is not in the strict sense "stillborn." This definition, which is that em- ployed in United States vital statistics, runs counter to current Japanese usage, under which infants who showed signs of life at birth but never succeeded in establishing a pattern of regular respiration are frequently reported as stillborn. This usage was in part a matter of convenience, since a stillbirth required com- pleting only one official form, whereas a live- birth dying an hour following delivery required completing two. The subject of the ABCC's usage of the term "stillbirth" was repeatedly taken up at conferences with the midwives. The frequency of stillbirths encountered in our control material (both parents category 1) was in Hiroshima 1.27 per cent of all births (17,189 births) and in Nagasaki 1.31 per cent (14,450 births). In comparison, in 1950 the "official" stillbirth rate (stillbirths per 1,000 livebirths) was in Hiroshima prefecture 79.6 and in Nagasaki prefecture 87.7, or, expressed as percentage of all births, 7.37 per cent and 8.07 per cent respectively (Public Health and Welfare in Japan, 1950~. Official statistics for other years are similar. There is apparent a marked discrepancy between official statistics and our own. There are at least five factors to be taken into account in an evaluation of these differences. Firstly, there is the matter of recis- tration practices referred to above. Secondly, the official stillbirth data are for stillbirths after the third month of uterogestation, whereas by and large our figures refer to events following the fifth month of gestation. Thirdly, since the official figures are for an entire prefecture, there is the possibility of urban-rural differentials. ~8 This, however, works in the opposite direction than the first two factors, since in 1950 the stillbirth rate for all ski (cities) was 134.0 per 1,000 livebirths, whereas for all gun (villages and rural areas) the rate was 70.4. Fourthly, the official figures may include some induced termi- nations, whereas these were excluded from our own data. Lastly, those stillborn infants with gross malformations were excluded from our figures. The reasons for this exclusion were given in Section 6.2. When approximate allowance is made for the exclusion from our figures of stillborn, malformed infants, the stillbirth rates observed in this study are quite similar to those currently obtaining in many parts of the United States (e.g., Michigan, 1950, 1.9 per cent). The possi- bility that the ABCC program was failing to obtain data on any substantial number of still- births seems precluded by the efficiency of preg- nancy registration (Sec. 2.1) and the system of careful follow-up for all registered terminations. 9.2 The genetic artz~mer~t for radiation-ir;- duced changes. Animal experimentation on the genetic effects of irradiation indicates that the largest group of induced mutations having clear-cut effects detectable in the first generation of offspring following exposure are the auto- somal lethals. As detected in the first genera- tion of offspring these mutations would consist largely of the dominant lethals, although a few recessive lethals would be recovered due to the fortuitous combination in some individuals of an induced lethal mutant with an allelic lethal mutant of spontaneous origin. Presumably one of the manifestations of the presence of these mutant genes would be fetal death. Accordingly, we might expect, as one of the changes sympto- matic of irradiation-induced genetic damage, an increase in the frequency with which infants are stillborn as parental exposure increases. 9.3 Cor~comitc~nt ~ariatiorl knower to affect

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Analysis of the Stillbirth Data the stillbirth rate.-No one of the indicators with which we have dealt or shall deal is more complex with respect to concomitant variation than the one presently under consideration. No less than seven sources of concomitant variation known to affect the stillbirth rate could, con- ceivably, be influencing the data which we shall analyze. These seven sources of extraneous vari- ation are congenital syphilis, birth injury, ma- ternal age, parity, nutrition, rate of reproduc- tion, and paternal age. Congenital syphilis has long been one of the major causes of fetal mortality. In Hiroshima and Nagasaki the frequency of positive serolo- gies is from 5 to 7 per cent among post-parturi- ent women. To assess the amount of infantile mortality attributable to congenital syphilis among the births described here would have required an expenditure of time and energy which, because of the limitations of personnel 119 by syphilitic stillborn infants (and we have no evidence that it is not) then, because of the known differential in maternal age among the parental exposure cells, herein lies a possible source of bias. The age distribution among the exposure cells is such that this bias would tend to inflate the stillbirth rate among those parents less heavily exposed or not exposed at all. How- ever, these potential effects would appear to be quite small, of a magnitude which could safely be ignored in this analysis. A second major factor affecting infant sur- vival (which it was not possible to control) is the occurrence of an injury during parturition. In the United States, it has been estimated that birth injury accounts for no less than 13.6 per cent of infantile mortality (Stander, 1941~. Of the various types of injuries which may be sustained during the passage of the infant through the birth canal, by far the most common TABLE 9.1 CONGENITAL SYPHILIS AMONG LIVING INFANTS BORN IN NAGASAKI IN 19 51 (Incidence and relation to maternal age [after Wright, S.w. et al., 19523) Maternal age: years Totals Number of living infants6,673 Number of cases of congenital syphilis 47 Incidence X 1,000 7 %2_ 11.160 1 5-19 2~24 181 1,691 4 22 and facilities, was not possible. However, a small study was made in Nagasaki on infants born in the year 1951 in an attempt to deter- mine the incidence of congenital syphilis among the infants being examined in connection with the genetics program (Wright, S. W. et al., 1952~. Initially it was planned that this study would estimate the incidence of congenital syphilis among living infants, stillbirths, and neonatal deaths. Because of the formidable diffi- culties posed in estimating the latter incidences in the absence of an exhaustive post-mortem program in Nagasaki, attention had to be fo- cused on living infants alone. Two items of interest here emerged from this study. Firstly, some seven out of every thousand liveborn infants were shown to have congenital syphilis either by clinical, serologic, or roentgenologic examination, or any combination thereof. Sec- ondly, a gradual decline in the rate of trans- mission with increasing maternal age was noted. These latter data are reproduced in Tame 9.1. If this same effect of maternal age is exhibited 17 10 DF= 5 25-29 2,435 16 6.5 30-34 1,456 35-39 735 5 4 3.4 5.4 P < 0.05 40 44 171 5.8 45-50 o o is intra-cranial injury with hemorrhage. It has been reported that 40-80 per cent of infants coming to autopsy will show evidence of this form of birth injury (Stander, 1941~. In our own data among 50 autopsied infants, se- lected at random, 26 showed intra-cranial hemorrhages ranging from moderate to severe in degree. While the importance of birth injury in infantile death cannot be gainsaid, it is di~- cult to visualize circumstances which would lead to a non-random distribution of birth injuries among the parental exposure categories, and this possibility will be ignored in the analysis. A third major factor affecting infant survival is maternal nutrition. The importance of this variable is amply attested to by an extensive literature. In the main, this literature is in agree- ment in indicating that rather drastic changes in maternal nutrition must occur before clearly demonstrable changes in the stillbirth rate can be shown (see, for example, Antonov, 1947, and Smith, 1947~. There is no evidence that during the course of this study the limitations

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120 Genetic Effect of imposed on maternal nutrition by economic conditions prevailing in Japan reached the levels necessary to produce measurable changes in the stillbirth rate, or that (arguing again from the rough classification of economic status presented in Sec. 5.3) such differences in maternal nutri- tion as existed were non-randomly distributed. Among the variables affecting the stillbirth rate previously enumerated, the effects of ma- ternal age and parity are by far the most com- plex and general in scope. These effects as TABLE 9.2 THE EFFECT OF MATERNAL AGE AT FIXED PARITY (The meaning of the symbols employed it Atomic Comics Chapter IX manifested in the present material are sum- marized in Tables 9.2 and 9.3 and Figures 9.1 and 9.2. The data are presented and analyzed in the same manner as age and parity effects with respect to major congenital malformations (cf. Sec. 8.4~. Again, a detailed discussion of the findings will be deferred for a subsequent publi- cation. There is a significant effect on stillbirth frequency of both age and parity, with, in both instances, an apparent increase in stillbirth fre- quency at the extremes of the scale. This in ON THE FREQUENCY OF STIT [BORN INFANTS explained in Sec. 8.4.) Total Normal Stillborn Per cent births births infants stillborn AD Parity 1 < 21 1,9121,882 30 1.57 .01995 21-25 8,6238,479 144 1.67 .05687 26-30 3,1923,125 67 2.10 .03101 31-35 614595 19 3.09 .02920 36-40 ............ 178} 189 17} 4.06 .01661 ....... ... ... ......... ... ~ Total 14,538 14,270 268 .15364 X 5 = 14.046* IAD = 0.0768 PT = 0.2612 Parity 2 <21 ......................... 421 415 6 1.43 .01095 21-25 ......................... 6,639 -6,572 67 1.01 .00615 26-30 ......................... 6,354 6,294 60 0.94 .03259 31-35 ......................... 1,415 1,399 16 1.13 .00983 36-40 ......................... 366 360 6 1.64 .01460 41 + 47 46 1 2.13 .00336 ~- Total 15,24215,086 156 .07748 X25 = 3.174 IAD = 0.0387 PT = 0~2738 Parity 3 21-25 36} 2,224 23} 1.02 .03634 26-30 ......................... 5,799 5,729 70 1.21 .01513 31-35 ......................... 2,390 2,357 33 1.38 .02444 41 + . 66} 580 11} 1.86 .02703 Total 11,027 10,890 137 .10294 X23 ~ 3.153 IAD = 0.0515 PT = 0.1981 Parity 4 21-25 478}4766} 1.45 .02010 26-30 .........................2,8482,82820 070 .16468 31-35 .........................2,5212,48734 1.35 .07112 36-40 .........................75073614 1.87 .07286 41 + 84 83 1 1.19 .00060 Total 6,686 6,610 76 .32936 X24 = 9.770 Ion = 0.1647 PT = 0.12O1

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Analysis of the Stillbirth Data TABLE 9.2 Continued Total Normal Stillborn Percent births births infants stillborn AD Parity 5 21-25 7876 2 2.56 .01723 26-30 991975 16 1.61 .03879 31-35 1,7561,737 19 1.08 .11020 36-40 837823 14 1.67 .04208 41-- 9795 2 2.06 .01211 Total3,7593,706 53 .22041 X24 = 3.~16 IAD = 0.1102 PT = 0.0675 Parity 6 26-30 262T 270 3) 1.46 .00158 31-35 956 943 13 1.36 .03585 36-40 794 785 9 1.13 .08678 41 + 141 135 6 4.26 .12421 Total 2,165 2,133 32 .24842 X23 = 8.208* IAD = 0.1242 PT = 0.0389 Parity 7 + 21-25 4) 58 2T 4.92 .02803 31-35 488 479 9 1.84 .05538 36-40 1,195 1,167 28 2.34 .02451 41 + 498 483 15 3.01 .05188 Total 2,242 2,187 55 .15980 X23 = 3.015 IAD = 0.0799 PT = 0.0403 All parities < 21 2,374 2,337 37 1.56 .00507 21-25 18,045 17,801 244 1.35 .01032 26-30 ; 19,503 19,265 238 1.22 .04472 31-35 10,140 9,997 143 1.41 .00189 36-40 4,645 4,556 89 1.92 .03153 41 + 952 926 26 2.73 .01659 Total 55,659 54,882 777 XO5 = 26.547*. IAD, (forage) = 0.0761 crease at the lower end of the scale is more definite with respect to parity than with respect to age. One of the more exhaustive previous studies of this relationship of maternal age and parity to infant survival is that of Yerushalmy (1945), who found that (1) "the lowest rates do not occur in one particular age group irrespective of parity. There is a consistent shifting of the minimum rate to the older ages with increasing parity." (2) "When the stillbirth rates by age of mother are compared for the different parity groups the increase in the rate is not propor- tionate for the various age groups. The increase is very much higher for the younger age of mother groups than for the older." The present data appear to agree with the first of these two conclusions, but of themselves would scarcely permit drawing the second conclusion- this may be in part a matter of the numbers involved. From the standpoint of controlling extraneous variation, these findings, taken in conjunction with our own, imply that the only really ade- quate control is one which takes into account not only maternal age but also parity. Among the Japanese data, to effect an adequate control would require recognizing approximately 25 parity-specific age intervals (five intervals for parity, and five for age, or 25 in all). The data, because of the already existing numerous ways

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22 Genetic Efects of Atomic Bom bs Chapter IX TABLE 9.3 THE EFFECT OF ~ATERNAL PARITY AT FIXED AGE ON THE FREQUENCY OF STILLBORN INFANTS (The meaning Of the SYmbO1S emP1OYed iS eXP1ained in SeC. 8.4.) MOther'S age: < 21 TOta1 NOrma1 Sti11bOrn Per Cent birthS birthS infantS Sti11bOrn AD 1,912 1,882 30 1.57 .00551 421 415 6 1.43 .01542 41 40 1 2.44 .00991 TOta1 2,374 2,337 37 - .03084 X22 = 0.257 IAD = 0.0154 PT = 0.0427 MOther'S age: 21-25 1 8,623 8,479 144 1.67 .11384 2 6,639 6,572 67 1.01 .09460 3 2 211 2 188 23 1.04 .02865 . . . . . . . . . . .. . ... 4 478 472 6 1.26 .00193 5 78T 90 4 4.26 .01133 6+ 16F TOta1 18,045 17,801 244 .25035 X24 19.969** IAD = 0.1252 PT = 0.3242 MOther'S age: 26-30 1 3 192 3 125 67 2.10 .11930 . . . . . . . . . . . . . . . 2 ............................. 6,354 6,294 60 .94 .07461 ~5 799 5 729 70 1.21 .00326 , ............................. . . 4 ............................. 2,848 2,828 20 .70 .06276 S 991 975 16 1.61 .01662 . .. . .. . .. . .. . .. . . . . .. . . . . .. . . 6 262 259 3 1.15 .00083 71 57 55 2 3.51 .00555 T . TOta1 19,503 19,265 238 - .28293 X26 = 34.577~: * IAD = 0.1415 PT = 0~3504 MOther'S age: 31-35 1 ............................. 614 595 19 3.09 .07335 2 ............................. 1,415 1,399 16 1.13 .02805 3 ............................. 2,390 2,357 33 1.38 .00500 4 2 521 2 487 34 1.35 .01101 . . . . . . . . . . . . . . . . . . . . . . . 5 ............................. 1,7561,73719 1.08 .04088 6 95694313 1.36 .00342 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 48847991.84 .01503 TOta1 10,1409,997143- .17674 X26 = 15.444* IAD = 0.0884 PT = 0.1822 MOther'S age: 36~0 1 178 171 7 3.93 .04112 2 366 360 6 1.64 .01160 . . . . .. . .. . . . .. . . . . . .. . . . .. . .. ~525514 112.10 .01077 ~ 4750736 141.87 .00435 . .. . . . .. . . . .. ... . . .. . .. .. . .. . 837823 141.67 .02334 5 6 794 785 9 1.13 .07118 7 + 1,195 1,167 28 2.34 .05846 ........................ 4,645 4,556 89 - .22082 X245 _ 8.111 IAD = 0.1104 PT = 0.0835

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A nalysis of the Stillbirth Data TABLE 9.3 Continued Mother's age: 41 + 123 Total Normal Stillborn Per cent births births infants stillborn AD 19 18 1 5.26] 47 46 1 2.13 ~.06346 66 -66 - - ~ 84 83 1 1.19 .05117 97 95 2 2.06 .02567 141 135 6 4.26 .08499 498 483 15 3.01 .05533 ........................ 952 926 26 - .28062 X24 = 3.030 IAD = 0.1403 PT = 0.0171 All ages 1 ............................. 14,538 14,270 268 1.84 .08491 2 ............................. 15,242 15,086 156 1.02 .07411 3 ............................. 11,027 10,890 137 1.24 .02211 4 ............................. 6,686 6,610 76 1.14 .02263 5 ............................. 3,759 3,706 53 1.41 .00068 6 ............................. 2,165 2,133 32 1.48 .00231 7 + 2,242 2,187 55 2.45 .03094 Total 55,659 54,882 777 X26 = 59.978** IAD" (for parity)=0.1186 s.o 4.5 4.0 3.s 3.0 2.5 ST ILL BIRTHS (PER CENT) 2.0 .5- l 1 n. . . 0.5 '. / '5 20 25 30 35 MOTHER S AGE PARITY - 7. 6 __ _ s \ ~I -- 4 \ / I ...... 3 J / . ~ 1 \ / .~/ 40 45 FIGURE 9.1 The distribution of the frequency of stillborn infants by age of mother for specified parities.

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124 4.5. STI LLBIRTHS (PER CENT) 4.0+ 3.~ - 3.0 2.5 2.0 1.5 1 .0 0.5 1 2 FIGURE 9.2 The distribution of the frequency of of classification, would not permit so elegant an approach to the extraneous variation occasioned by mother's age and parity. Accordingly, it became a matter of judgment as to which of these two factors was to be controlled. A de- cision was reached to disregard age but to recognize, for analytical purposes, five parity classes, namely, parity 1, parities 2-3, 4-5, 6-7, and 8 and higher. 9.4 The data.-Tables 9.4 and 9.5 present the distribution and analysis of stillborn infants by sex, city, and parental exposure without fur- ther subdivision by parity. Inspection of Table 9.4 suggests a difference in the stillbirth rate when the mother was not exposed as opposed to when she was. From the analytical table (9.5a) we note a significant effect of mother's exposure but not of sex or father's exposure. Attention is called to the fact that the sex- mother's exposure interaction is not significant, in contrast to expectation in view of the possi- ble effect of exposure on the sex ratio described in Chapter VII. With regard to the reality of the effect of mother's exposure on the stillbirth rate, it should be borne in mind that these data Genetic Efecis of Atomic Bombs Chapter IX MATERNAL AGE , \ 36-40 1 ~ ~ ~ - 31 - 35 1 ....... - 26-3.0 1 - - - - 21-25 1 1 i 1 1 \ /\l ,,.''/ ~ ,_~ . _ . _ , . . . 3 4 5 6 PARITY 7+ stillborn infants by parity for specified maternal ages. are uncorrected for parity and the more heavily exposed cells are biased in a way which would increase the stillbirth rate in these cells. If in the analysis of Table 9.4 we limit our attention to those exposure cells in which both parents were exposed, which would reduce the differ- ences between cells with regard to parity, the apparent effect of maternal exposure disappears (see Table 9.5b). This observation is of con- siderable importance in the interpretation of these data since (a) maternal exposure con- founds the effects of genetic and somatic damage and hence a significant effect of maternal expo- sure not reflected in paternal exposure might well be a somatic rather than a genetic effect, and (b) there is evidence which has been pre- sented in Chapter V and elsewhere in this report that the comparison of pregnancy ter- minations occurring to exposure category 1 par- ents with terminations occurring to parents in any other exposure category is biased. Let us now turn to a consideration of what these data reveal when the sex of the infant is ignored but terminations are classified with re- spect to parity. Tables 9.6 and 9.7 present the

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Analysis of the Stillbirth Data TABLE 9.4 FREQUENCY OF STILLBIRTHS BY SEX, PARENTAL EXPOSURE AND CITY (Unrelated parents) Male infants Hiroshima Fathers v, ~ . 4J - o 1234-5Total En8,91976130920810,197 14 s1141052131 l P.0128.0131.0162.0096.0128 En2,7969241951214,036 2/ s3615S561 lop.0129.0162.0256.0413.0151 En1,108220266801,674 3] s2718137 tp.0244.0045.0301.0125.0221 En5651085256781 4-5/ s14 1 15 tp.0248 .0192-.0192 in13,3882,01382246516,688 I Total s19126198244 p.0143.0129.0231.0172.0146 Male infants Nagasaki Fathers 125 1234-5Total rrn7,5271,108125738,833 1: s1102111133 tp.0146.0190.0080.0137.0151 En4,8092,0871401037,139 2] s77323 112 tp.0160.0153.0214 .0157 ~En3551325013550 =~; 3gs 6 1 7 tp .0169 .0076 -.0127 En 276 56 18 15365 4-5gs 2 1 3 ~ p .0072 .0179 .0082 En12,9673,38333320416,887 Total~s1955541255 tp.0150.0163.0120.0049.0151

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126 Genetic Effects of Atomic Bombs Chapter IX TABLE 9.4 Continued - Female infants Hiroshima ,-- ~ Fathers cat o by Total: , ~ 1234-5Total rn 8,1907202801839,373 1g s 104996128 (p .0127.0125.0321.0328.0137 rn 2,5128971861213,716 2\ s 46114364 (p .0183.0123.0215.0248.0172 in 1,060202248761,586 33 s 2132127 tp .0198.0149.0081.0132.0170 in 539915560745 5gs 61 29 l P .0111.0110-.0333.0121 in12,301 1,91076944015,420 is177 241512228 p.0144 .0126.0195.0273.0148 Female infants Nagasaki . , - Fathers , ~ 1 234-5Total rn 6,923 1,040112648,139 14 s 80 17 97 tp .0116 .0163--.0119 En 4,430 2,016133736,652 24 s 57 4923111 p .0129 .0243.0150.0411.0167 En 382 1424321588 34s 9 3- 12 tp .0236 .0211 .0204 (n 276 \601713366 4-5gs 4 21 7 (p .0145 .0333.0588-.0191 En12,0113,25830517115,745 Totals s1507133227 tp.0125.0218.0098.0175.0144

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Analysis of the Stillbirth Data TABLE 9.5 CHI-SQUARE ANALYSIS OF THE FRE QUENCY OF STILLBIRTHS BY SEX, PARENTAL EXPOSURE, AND CITY (Unrelated parents) a. All exposure cells (4 X 4) Source DF %3 P Total 63 92.343 .01-.02 Interactions, first order C M 3 .620 .80-.90 CF 3 10.626 .01-.02 CS 1 0.200 .50-.70 SM 3 1.565 .50-.70 SF 3 5.499 .10-.20 M F 9 5.548 .70-.80 Main effects Cities (C)a Mother's exposure 1... Mother's exposure-2... Mother's exposure 3... Mother's exposure 4, 5. Sum ............ 0.069 .70-.80 1 0.001 .95-.98 1 0.393 .50-.70 1 0.140 .70-.80 4 0.603 .95-.98 Sex (S)& Mother's exposure 1 1 0.725 .30-.50 Mother's exposure - 2 1 0.661 .30-.50 Mother's exposure 3 1 0.202 .50-.70 Mother's exposure- 4,5. 1 0.065 .70-.80 Sum ............ Mothers (M) ............ 4 1.653 .70-.80 3 12.797 .001-.01 Fathers (F)a Mother's exposure - 1 3 3.943 .20-.30 Mother's exposure- 2 3 6.769 .05-.10 Mother's exposure 3 3 4.192 .20-.30 Mother's exposure 4,5. 3 0.187 .95-.98 Sum 12 15.091 .20-.30 b. Excluding parents in category 1 (3 X 3) Total ............... Interactions, first order CM ............... CF .............. CS .......... SM ........ SF ........ MF .......... Main effects .S~sr {.S) 35 14.186 .50-.70 2 2.001 .30-.50 2 4.121 .10-.20 1 5.737 .01-.02 2 2.083 .30-.50 2 4.825 .05-.10 4 0.781 .90-.95 _ ~_, 1 1.884 Cities (C) 1 1.150 Mothers (M) 2 2.816 Fathers (F) 2 0.388 a Adjusted for mothers 127 .10-.20 .20-.30 .20-.30 .80-.9n

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Analysis of the Stillbirth Data distribution and analysis of stillborn infants by city and parental exposure with further sub- division by parity. It should be noted that, as expected, there are significant differences in the stillbirth rate among different parities. From Table 9.7 we further note that when all ex- posure cells are considered with reference to TABLE 9.7 CHI-SQUARE ANALYSIS OF THE FREQUENCY OF STILLBIRTHS BY PARENTAL EXPOSURE, CITY, AND PARITY (Unrelated parents) Total ................. Interactions, first order CM ................ CF ................. CP ................. ME ................. PM ................. PF ................. Main effects Parity (P) .......... City (C)'t ........... Mothers (M) n Parity Class 1...... Class 2...... Class 3...... Class 4...... Class 5...... DF X2 1S9 221.950 3 4 9 12 12 All classes 15 Fathers (F)a Parity Class 1 3 Class 2 3 Class 3 3 Class 4 3 Class 5 3 All classes 15 a Adjusted for parity. 0.620 10.626 8.925 5.548 9.060 16.085 too 1-.0 .80-.90 .01-.02 .05-.10 .70-.80 .50-.70 .10-.20 53 599 < .001 8.965 .10-.20 3 4.879 3 7.537 3 4.008 3 4.269 3 2.003 22.696 21.79 1.865 0.518 3.521 1.117 28.770 .10-.20 .05-.10 .20-.30 .20-.30 .50-.70 .05-.10 < .001 .50-.70 .90-.95 .30-.50 .70-.80 .o 1-.02 parity, there is no effect of city or of maternal exposure. However, an effect of paternal ex- posure significant at the 5 per cent level now appears. Inexplicably this latter effect seems to be largely, if not entirely, attributable to those fathers whose infants were firstborn. The fre- quency of stillbirths among firstborn infants by city and paternal exposure is presented in Table 9.8. The data suggest a regular increase in 129 stillbirth frequencies with increasing paternal exposure. To the end of determining whether this apparent effect was explicable in terms of the residual variation in maternal age not re- moved by the parity classification, Table 9.9 was prepared. An examination of this table reveals a number of points of interest. Of the five age groups investigated, the stillbirth rate increases with paternal exposure in three and decreases in two. In one of the three age groups (21-25) the increase with paternal exposure primarily TABLE 9.8 THE FREQUENCY OF STILLBIRTHS AMONG FIRSTBORN INFANTS BY CITY AND PATERNAL EXPOSURE (Unrelated parents) '1{S En 2lP ~rn =: As ~UP rn 4-54~s Cn Total~s City Hiroshima Nagasaki 8,1625,937 15989 .0195.0150 8031,125 1834 .0224.0302 344113 132 .0378.0177 21352 1.11 .0516.0192 9,5227,227 201126 .0211.0174 Total 14,099 248 .0176 1,928 52 .0270 457 15 .0328 265 12 .0453 16,749 327 .0195 reflects a "1" vs. "non-1" difference. In sub- stance, then, when maternal age as well as parity is taken into account, there emerges no clearly consistent relationship between paternal ex- posure and the stillbirth rate. 9.5 Summary. Analysis of the stillbirth data, taking into account differences between exposure cells in the parity distributions, fails to reveal significant differences between cities or consistent significant effects of parental ex- posure. The deviations from expectation ob- served are so small and inconsistent that they can scarcely be labeled as favoring or not favor- ing genetic hypothesis.

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130 Genetic Effects of Atomic Bombs Chapter IX TABLE 9.9 THE FREQUENCY OF STILLBIRTHS AMONG FIRSTBORN INFANTS BY PATERNAL EXPOSURE AND MATERNAL AGE (Unrelated parents) Fathers X22 Maternal , age 1234-5Total J n 1,77235678292,23S] <20 s 2981 38 ~1.055 ip .0164.0225.0128-.0170J fn 8,5051,0312471419,924] 21-25> s 1382673174 ~5.908 UP .0162.0252.0283.0213.0175] On 3,10037284563,612] 26-30/ s 6385480 ~11.962~* up .0203.0215.0595.0714.0221 J On 5641092926728] 31-35]s 137-121 ~5.768 up .0230.0642-.0385.0288 J On 144511611222 ~ 36-404 s 431412 ~11.047** up .0278.0588.0625.3636.0541 ~ (n 1493228] 41 +] s 1-1 2 ~- up .0714 .3333 .0714] En14,099 1,928 457 265 16,749] Total~s248 52 15 12 327 lP.0176 .0270 .0328 .0453 .0195 J t Classes 3 and 4-5 are pooled.