The birth of twins is a real miracle of the nature. Two persons, as like as two peas similar at each other, always attracted interest and admiration. Since ancient times twins were considered the elected people.
As there is a conception of twins
The children who were born at one mother at the same time are considered as twins. When the woman bears several children - it is called polycarpous pregnancy. It arises: if the zygote - the impregnated ovum is divided into two and more parts if the ovum has two and more kernels, and all of them were impregnated by several spermatozoa if several ova were impregnated by spermatozoa.
Twins can be monoovular and raznoyaytsevy. In the first case children have one genotype, are absolutely identical because the zygote was divided into two genetically identical half with one hereditary potential. Such twins have identical hair color, the form of lips, the physical building, identical fingerprints. At raznoyaytsevy the big percent of similarity, but nevertheless is visible and invisible distinctions because germs developed from different ova which were at the same time impregnated.
Statistics
Statistics says that one birth of twins is the share of 100 childbirth. Two thirds of all number of newborns - nonidentical twins. The heredity certainly defines a possibility of polycarpous pregnancy at the woman, but there is some other factors. Monoovular can be conceived at the lady at any age, and here raznoyaytsevy most often appear at women aged from 35 up to 45. It is explained by reorganizations in a female body. The race defines a possibility of polycarpous pregnancy too. At the black the twins are born very often, and here in Mongoloid race is very exceptional case.
Repeated ovulation
At some women several ovulations in a menstrual cycle are observed, this natural opportunity also gives the chance to conceive twins. Probability of polycarpous pregnancy increases through one generation. If in a sort there were twins (in the female line), then chance to conceive twins in 10 times more. Administration of drugs stimulating work of ovaries can lead to several ovulations in one cycle. Hormonal therapy which is appointed for treatment of infertility often turns into conception of twins. The procedure of artificial insemination implies input in a uterus to six embryos, and many of them can successfully take root. Conception of twins is connected often with external data of the woman. At high and full according to twins more often are born. During breastfeeding there are changes in an ovulyatsionny cycle, and the woman can soon find polycarpous pregnancy. It is not obligatory to have genetic predisposition for this purpose.