Reduction in live births in Japan nine months after the Fukushima nuclear accident: An observational study

Abstract

Background: After the Chernobyl accident on 26 April 1986, a drop in birth-rate was found in several European countries in the first quarter of 1987. The objective of the present study was to investigate whether a similar drop in live births occurred in Japan after the Fukushima nuclear accident.

Data and methods: A study region was defined consisting of Fukushima prefecture plus 10 nearby prefectures. The observed monthly numbers of live births (LB) in October 2011 through December 2012 were compared with the predicted numbers determined from the trend of live births in the remaining months from January 2006 through December 2018. The study region was divided into Fukushima plus three adjacent prefectures (Area A, assumed effective mean dose in the first year 1 mSv) and seven surrounding prefectures (Area B, 0.5 mSv). The rest of Japan (Area C) served as the comparison (control) region (0.1 mSv). A combined regression of live births (LB) in areas A, B, C was conducted with individual trend parameters but common parameters for monthly variations.

Results: In the study region as a whole (areas A and B combined) a highly significant 9.1% (95% CI: -12.2%, -6.0%) drop in LB was found in December 2011. Reduced numbers of live births were also observed in October-November 2011 (-3.3%, p = 0.006), i.e. in births exposed early in pregnancy. In the second quarter of 2012, i.e. in live births conceived more than 3 months after the Fukushima accident, the decrease was greater (-4.3%, p < 0.001) than in the first quarter (-1.6%, p = 0.11). i.e. in those conceived within the first three months after the accident while no significant decrease was detected in the third (-0.7%, p = 0.44) and fourth (-0.5%, p = 0.62) quarters. The effect in Dec 2011 was greater in Area A with -14.0 (-17.6, -10.3) % than in Area B with -7.8 (-11.1, -4.5) % and non-significant in Area C with -1.3 (-4.2, +1.6) %, p = 0.38. The combined regression of the data in areas A, B, and C found a highly significant association of the effect in December 2011 with radiation dose. Conclusion: It is suggested that the observed drop in LB in December 2011 may reflect early deaths of the conceptus from high radiation exposure following the triple meltdown at the Fukushima Daiichi nuclear power plant on March 12-15, 2011.

Fig 1. Map of prefectures around Fukushima Daiichi Nuclear Power Station (FDNPS).

Area A (shaded dark grey): Prefectures Fukushima (7), Miyagi (5), Tochigi (9), Ibaraki (8); Area B (shaded light grey): Prefectures Iwate (3), Akita (4), Yamagata (6), Niigata (15), Gunma (10), Saitama (12), Tokyo (13), Chiba (11).

Fig 2

Panel A: Monthly numbers of LB from Japan, 1993–2018, and result of a Poisson regression of the data from 1997 to 2011 (black dots) with a linear-quadratic time trend. The broken line shows the extrapolated trend line. Panel B: Deviations of the observed numbers from the predicted trend in units of standard deviations (standardized residuals).

Fig 3

Panel A: Monthly numbers of LB in the study region, 2006–2019, and trend line. Panel B: Deviations of the observed numbers from the expected trend in units of standard deviations (standardized residuals). The black circles show the data in the time window (Oct 2011 through Dec 2012); the broken vertical line denotes March 2011.

Fig 4

Panel A: Monthly numbers of LB in Japan minus the study region (Area C), 2006–2019, and trend line. Panel B: Standardized residuals. The black circles show the data in the time window (Oct 2011 through Dec 2012); the broken vertical line denotes March 2011.

Fig 5. Reduction in live births in Dec 2011, Oct/Nov 2011, and Q2 2012 as a function of estimated mean effective dose.

The error bars show standard errors of the estimate.