The problem of differential prevalence of congenital malformation and reproductive losses in Ukrainian populations becomes especially relevant in the context of increasing the impact of environmental and genetic and demographic factors that can influence their gene pool. The purpose of the study is to determine, during long-term monitoring, the statistically significant differences between the rural populations of Kherson oblast on the incidence of birth defects, involuntary miscarriages and stillbirths, in order to further identify the causes of detected heterogeneity. In calculating the frequency of these indicators in urban and rural populations, the materials of the regional medical-statistical register (medical form 21, 13, 49) are used. The statistical computation of the results obtained (calculation of confidence intervals and the reliability of the differences) was carried out using STATISTICA and Microsoft Excel 9-2000 programs. It has been established that there are significant differences between urban and rural populations in the prevalence of congenital malformations and reproductive losses. In Kherson, for the period of 2000–2013, the average incidence of developmental defects (37.8±11.3‰) and stillbirths (8.2±1.1‰) significantly exceeded similar rates in rural populations (respectively 23.9±1.4‰ and 4.8±0.6‰). However, in rural populations, the incidence of involuntary miscarriages was significantly higher (31.2 ± 1.9 ‰) than in the oblast center (18.9 ± 2.1 ‰). In addition, according to these indicators there is a significant differentiation between rural populations. The prevalence of birth defects in infants in the region is due to an increase in the frequency of “model” defects (r=0.69, p<0.05), which have a significant hereditary component. It was found that in the urban Kherson population, the relatively high frequency of postnatal violations testifies to the weakening of the “sifting” effect of natural selection. On the contrary, selection in rural populations eliminates most of the non-viable embryos in the early stages of pregnancy, as evidenced by the relatively high prevalence of involuntary miscarriages. In the long term, it is necessary to establish the correlation between the indices of the incidence of congenital and hereditary pathology in populations and the parameters of their genetic and demographic structure.

In modern conditions of constant population decline and the presence of adverse demographic processes in Ukraine, the urgent task is to identify the most significant genetic and demographic factors affecting the adaptation of the population, as well as monitoring changes in the volume and structure of the genetic load caused by congenital pathology. The frequency of congenital malformations of newborns in the Kherson region increased (from 22.3±5.4 % in 2000-2008 to 40.1 ± 8.2 % in 2009-2017). In recent years, there has been a statistically significant increase in the frequency of hereditary pathology of newborns among the rural population of the region (from 1.09 to 1.95 %).The total frequency of congenital malformations increased in almost all areas of the Kherson region (from 20.2±1.4, 27 to 27.6±1.3 %) and averaged 30.2±6.4 %. Significant differences in this indicator were found between some nations of the region. Malformations of the circulatory system (28.5 %), musculoskeletal system (26.05 %) and the genitourinary system (15.25 %) occupy a leading place in the structure of congenital pathology. The prevalence of congenital malformations is inversely correlated with the prevalence of spontaneous miscarriages (r =-0.52± ±0.12; tr=2.4> t05=2.12), which indicates the presence of a screening effect that eliminates non-viable genotypes in embryonic period of ontogenesis.Rural population where the share of interethnic marriages has increased over the years of research, is characterized by a higher prevalence of congenital malformations (r=0.50±0.46; t=2.3>t05=2.12). In population (with an endogamy index of 0.5 and higher), an increase or relative constancy of the proportion of homolocal mono-ethnic Ukrainian marriages and a lower prevalence of congenital malformations among newborns are observed. The level of endogamy does not significantly affect the prevalence of malformations (r=-0.20±0.24; tr=0.8