This is the first population-based study that examined chronological trends for pregnancy outcomes after a major disaster. Although the response rate in 2011 was the highest, especially in the Soso district, where the most damage occurred, the response rate tended to decrease over the years, with more than 50% reported in 2018. We also found a trend increase in mean maternal age, rate of conception after sterility treatment, and rate of cesarean delivery over the years. There were no distinct changes in the trend of occurrence regarding PTB, LBW, and fetal anomaly.
The response rate in this study was approximately 50%, and this varied significantly over the years and between the districts. While Kenpoku constantly had a higher response rate than other districts, Soso had a higher rate only in 2011. This difference may be related to their concern that pregnant women in Kenpoku and Soso districts were exposed to relatively higher radiation doses. Disasters potentially influence a range of reproductive outcomes [8]. Many studies examined the effects of exposure to disasters on pregnancy outcomes, and these exposures were usually from so-called “attacks” such as the World Trade Center disaster, the bombing attack in Serbia, and the Madrid train bombing; environmental and chemical disasters such as the Bhopal gas release in India, the Three Mile Island accident, and the Chernobyl accident; and natural disasters such as earthquakes, hurricanes, floods, and ice streams [3]. The Great East Japan Earthquake and Fukushima Daiichi nuclear accident form a complex disaster. They included natural disasters such as the Great Earthquake and tsunami and environmental/technical disasters such as the nuclear power plant accident.
The association between environmental/chemical disasters with the risk of PTB and fetal growth is conflicting. Goldman et al. reported that the Love Canal disaster in the United States did not show any increased risk of PTB among 227 residents [9]. However, Levi et al. reported that the Chernobyl accident affected the shortened gestational age among 88 mothers of Swedish women who were anxious at the time of the disaster [10]. In conflict with our study, the earthquake disaster in China increased the risk of PTB. Tan et al. compared PTB incidence with 6,638 pregnant women before the disaster and 6,365 pregnant women after the disaster [11]. The incidence of PTB was 5.6% and 7.4%, respectively, and was significantly high after the disaster (p < 0.01) [11]. In the whole of Japan, the number of high-risk women for obstetric complications is increasing along with increasing maternal age at first pregnancy [12–14]: the incidence of PTB pregnancy week (5.7%) and LBW < 2,500 g (9.4%) is approximately stable after the disaster [15]. The risk of PTB at Fukushima prefecture after the Great East Japan Earthquake is also conflicting. Hayashi et al. have reported no significant increase in the incidence of PTB < 37 weeks in the first year of the disaster among all pregnant women in Fukushima prefecture, using the same FHMS data [16]. At the time of the disaster, many pregnant women were forced to evacuate suddenly, which caused depressive symptoms in mothers [4, 17]. In relation to these depressive symptoms, Suzuki et al. have reported that the pregnant women who changed perinatal examination facilities by medical adaptation were significantly associated with shortening (β = -10.6, P < 0.001) of the gestational period and PTB (adjustment odds ratio 8.5, 95% confidence interval 5.8–12.5) compared to women who visited only one facility at Fukushima prefecture after the disaster [18].
The association between the environment or a natural disaster and fetal growth is also conflicting [16, 19–22]. Regarding fetal growth, we have reported no evidence that the Great East Japan Earthquake and the Fukushima Daiichi nuclear accident increased the risk of fetal growth restriction in Fukushima after the first year of the disaster [5].
Using an institution-based investigation of the coastal area where the most catastrophic damage occurred [4], Leppold et al. reported no increased proportions of PTBs or low birthweight in any year after the disaster (merged post-disaster risk ratio of PTB: 0.68, 95% CI: 0.38–1.21 and low birthweight birth: 0.98, 95% confidence interval: 0.64–1.51) [23]. In Japan, pregnant women may have better access to relief programs or receive adequate support from their families, society, and government during the disaster [4].
The effect of disasters on congenital anomalies is the main public concern. Some studies have reported that disasters are related to congenital abnormalities. Examples of the disasters include a nuclear reactor accident in Chernobyl in 1986 in Ukraine and a nuclear accident at Three Mile Island in Pennsylvania in 1979. A review of the influence of the Chernobyl disaster showed an increase in microchepalous and neural tube defects [24–26]. However, the incidence of major congenital anomalies did not increase in most European countries [27–29]. It was reported that 2–3% of all newborn babies had congenital abnormalities at birth [30, 31]. In Japan, from 2011 to 2016, the incidence of congenital disabilities was 2.43–2.59%, according to a report by the International Clearing house for Birth Defects Surveillance and Research) Japan Center [32]. Using a Japanese birth cohort study that included 12,804 pregnant women in Fukushima Prefecture, Kyozuka et al. reported that the prevalence of major congenital anomalies at delivery between 2011 and 2014 in Fukushima Prefecture was 1.6–3.2%, depending on maternal age [6]. Using the same data set as the present study, Fujimori et al. reported that the occurrence of congenital anomaly in Fukushima prefecture during the first year after the disaster was 2.72% (238/8672) [3].
Environmental endocrine disrupters, a group of compounds with potentially adverse health effects, are thought to be associated with cryptorchidism [33]. Kojima et al. decried the difficulties in clarifying the prevalence of cryptorchidism because of complexities in design settings for epidemiological surveys of this disease. They rejected the hypothesis that cryptorchidism increased in Japan because of the Fukushima Daiichi Nuclear Power Plant accident [34]. Hirai et al., using the All Japanese Cardiovascular Surgery Database, reported no increase in the number of patients with congenital heart disease from 2010 to 2013 [35].
Our study has several strengths. In Japan, few epidemiological studies involve pregnant women in a community, and our study is one of them. Large-scale studies and data supported by the government are considered valuable. In addition, we obtained relatively precise data on gestational ages and birth weights of the participants from their maternal and child health handbooks.
Nevertheless, this study has potential limitations. First, because the response rate was only approximately 50–60% through the study period, the actual incidence of adverse outcomes may have been overestimated if there was an overrepresentation of women affected the most by the disasters, especially pregnant women, in 2011 and 2012. Second, as this study used a self-administered questionnaire, it is assumed that the mothers answered correctly, especially regarding fetal anomalies. Third, this survey analyzed each district and failed to investigate the relationship with individual radiation exposure doses.
In conclusion, the findings of our study and those of previous studies indicated that there was little effect on pregnant women exposed to the Great East Japan Earthquake and other kinds of disasters during the first 8 years. Improving the understanding of the adverse reproductive effects of disasters requires as much preparedness as needed for an emergency response to prevent mortality and morbidity [4]. Further studies should be conducted to examine whether the disaster causes early pregnancy loss, such as miscarriage or abortion, and psychological complications.