Chernobyl: relationship between the number of missing newborn boys and the level of radiation in the Czech regions

Abstract

Background: The number of newborn boys was higher than that of girls in the Czech Republic each month from 1950 to 2005. The only exception was November 1986, when the number of newborn boys was significantly reduced. This has been explained by a selective negative impact of the Chernobyl accident in April 1986 on male fetuses during the third month of their prenatal development.

Objectives: The first and most radioactive cloud passed over the Czech Republic during 30 April-1 May 1986. Concurrent rainfall multiplied the radioactivity by up to > 10,000-fold in specific regions. We verified a hypothesis that the decrease in the male birth fraction in November 1986 correlated with the level of radiation in eight Czech regions after the Chernobyl disaster.

Results: We found a relationship between the level of radiation and the decrease in the number of newborn boys. The number of newborn boys was decreased in the six eastern regions where the radiation was strongly increased due to rain that accompanied the radioactive cloud. In contrast, the number of newborn boys was not reduced in the two western regions where the radioactivity was markedly lower.

Conclusions: A negative impact of radiation on the prenatal population was manifested as a selective loss of newborn boys in November 1986. This loss correlated with level of radioactivity. The 131I probably played the most important role because of its up-take during primary saturation of fetal thyroid by iodine, which accompanies the onset of the gland function in 3-month-old fetuses.

Keywords: atomic power station; birth seasonality; ecologic catastrophe; newborn sex ratio; pregnancy outcome; radiation; radioiodine; raining; spontaneous abortion.

Figure 1

Levels of radioactive fallout in the center of the East Bohemia region of the Czech Republic. Six radionuclides (iodine-131, tellurium-132, ruthenium-103, cesium-137, cesium-134, and lanthanum-140) were measured at 0700 hours on 1 May (during rainfall) and on 2 May (with no rain). Data from Kunz (1986).

Figure 2

Seasonal variation (mean number per month) in the annual rates of living newborn boys and girls in the Czech Republic calculated from 1950–1999 data. To eliminate the problem arising from the varying number of days in a month (e.g., 31 days in January, 28 or 29 in February) for a total of 600 months, we calculated the mean number of newborns per day; we used that number to calculate a mean value for each month in a year.

Figure 3

The percentage of boys among infants born in the Czech Republic in each November during 1950–2005. Only in November 1986 is the value < 50%, indicating that fewer boys were born than girls.

Figure 4

Seasonal variation in the annual percentage of spontaneous abortions officially registered in the Czech Republic. Values shown are percentage per month; total spontaneous abortions per year = 100%. Black circles indicate the percentage of spontaneous abortions calculated for each month during 1985, 1986, or 1987. Open circles indicate the mean annual rhythm calculated from data on spontaneous abortions in 1970–1999.

Figure 5

Schematic maps of the Czech Republic with delineated regions. Abbreviations: CB, Central Bohemia; EB, East Bohemia; NB, North Bohemia; NM, North Moravia; P, Prague; SB, South Bohemia; SM, South Moravia; WB, West Bohemia. (A) Passage of the first radioactive cloud over the country on 30 April (arrows) and the intensity of the rainfall measured from 0700 hours on 30 April until 0700 hours on 1 May 1986. (B) Distribution and level of radiation represented by ¹³⁷Cs; Note that the highest radiation deposit was in North and South Moravia, which reflects the areas of rainfall at the time the radioactive cloud passed over; the lowest radiation deposit was recorded in the areas outside the passage of the radioactive cloud, in North and West Bohemia, where the rain was absent or minimal. (C) The percentage of missing boys in each region during November 1986.

Figure 6

The fetal/maternal thyroid dose ratio in case of acute ingestion of ¹³¹I at different gestation stages (adapted from Berkovski et al. 2003). Note the enormous increase of the ¹³¹I content in the fetal thyroid during weeks 9–12 of prenatal development (gray bar).