Birth twins — a rather rare phenomenon, because the twins are only 2% of newborns. When the triplets were born, this is known throughout the city as the triplets are born, and even more rarely are already 2% of the births of twins.
Multiple pregnancy can be different. Not all children born as a result of a pregnancy are similar to each other. There odnoyaytsovye and dizygotic twins. Dizygotic twins have a resemblance to each other, like any brother and sister. Despite the fact that they develop in the uterus while the difference in the time of their conception may be from several hours to several days.
The twins develop from two fertilized eggs. They may be one and sexes. Identical twins are obtained with a single egg fertilized by one sperm cell, and then dividing the resulting embryos are formed independent.
While doctors can not determine the cause of this behavior of germ cells. Identical twins are so similar to each other that they sometimes can not distinguish between her own mother. Such twins are 5 times less likely than fraternal, and among them most are boys.
A special phenomenon — Siamese twins who have any common bodies or body parts. The reason for this phenomenon consists in that the splitting into separate embryonic form occurs later than in conventional twin origin, while, when the embryo is already partially formed. Conjoined twins — are extremely rare. They are produced once per 10 million births.
Embryos twins most "capricious"
Rare cases of multiple births is partly due to the fact that not all of them take root in the earliest days after conception. For a woman, it goes unnoticed, and she does not even know that was a "little bit" pregnant with twins. Found that only one out of 10 cases of conception and ends with a normal pregnancy leads to birth. To plan birth Twins impossible. But there are objective reasons that increase the probability of the birth of two or more babies at a time. And it applies only dizygotic twins, because probability Born identical twins are always constant. On average, it amounts to 3 cases per 1000 pregnancies.
Probability conceiving fraternal twins
So, the paramount woman's age. The older you are, the more your body produces hormones. A hormones stimulate oocyte maturation, hence, increasing the number of hormones increased probability maturation of multiple eggs are ready for fertilization. Therefore, for women aged 35-39 years, there is a real probability conceiving fraternal twins.
On the production of the hormone affects not only the age, but the length of daylight hours. The best time to conceive twins — spring, when the day is increasing and begins gently to warm sunshine.
Of great importance is heredity. For example, if a family already has twins, the probability to have another one pair of fairly large, but it decreases with distance in time generation of twins.
Ability to conceive twins passed only through the female line. Men can pass it to their daughters, but in the offspring of men themselves noticeable frequency of twins was observed.
There is also the effect of the duration of the menstrual cycle onconception twins. The greatest ability to give birth to twins have a woman whose menstrual cycle is very short — 20-21 days, and women with abnormalities of the uterus, such as having a septum in the uterus or bicornuate, like forked uterus.
Finally, twins and even triplets are often born by artificial insemination. This is also due to the use of hormonal drugs that stimulate egg maturation and ovulation. The emergence of a family of two or three children after years of infertility is not an uncommon phenomenon.
There is no explainable pattern of more frequent births in various social upheavals and wars. Maybe nature is so concerned about the preservation of man on earth.
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