How is the fetus formed?
Every month, an egg in my mother's body is discharged from the ovary to the fallopian tube, and the sperm army sent by my father rushes over. The first sperm soldier will meet the egg princess, and the two will combine into a fertilized egg, and the process of fetal formation will begin. The fertilized egg will enter the uterus and begin to divide, develop and grow.
Generally speaking, eggs and sperm combine one after another to develop into a baby, but there is a possibility of about 4/ 1000 to form twins.
Super alike twins
When an egg is combined with a sperm, it will undergo cell division and then form various parts of the body, but occasionally, this fertilized egg will first become two fertilized eggs within a week, and each fertilized egg will develop into a baby. Because these two babies are separated from a fertilized egg, their genes are exactly the same, the two babies are of the same sex and look alike, but the space occupied by the two babies in their mother's womb is different, which makes them look slightly different. This kind of twins is more common and is called "identical twins".
Sometimes, a fertilized egg may split into three, four or even five fertilized eggs, namely triplets, quadruplets and quintuplets.
Mirror twins
If the division of identical twins occurs not in the first week of fertilization, but in the second week, then the two babies not only look alike, but also may have mirror image characteristics. For example, one baby's dimples grow on the left and the other baby's dimples grow on the right; One baby is left-handed and the other is right-handed. If they (they) face each other, it's like looking at themselves in the mirror.
Twins with different looks
Marcia and Millie were born in England in 2006. Although they have completely different skin colors, one black and one white, and different looks, they are twins. Their father is black and their mother is white. The probability of intermarriage between different races is only one in a million, and it must be fraternal twins. When two little sisters tell others that they are twins, they always get booed, because it is so rare that people can hardly believe it, but life is so wonderful.
So, how are fraternal twins formed? Occasionally, my mother will send me two princess eggs, and two sperm soldiers in my father's sperm army will combine with them to form two fertilized eggs and develop into two babies, which are called "fraternal twins". These two babies come from different sperm and eggs. Like non-twin brothers and sisters, the gender is not necessarily the same, and the looks are not very similar, but the birth interval is very short.
conjoined twins
How would you feel if a "double-headed teacher" was teaching you? In a primary school in the United States, there is such a teacher, I should say two teachers, Abby (right shoulder) and Brita Ni (left shoulder) born in 1990. They teach fifth-grade children mathematics. They look like two-headed people, but in fact they are two people connected as one. Each of them has a heart, a stomach and a set of lungs, but * * * enjoys the liver, large intestine and reproductive system; Brita Ni controls the left arm and left leg, and Abby controls the right arm and right leg. So they have been coordinating a pair of movements since they were very young, and now they can cooperate perfectly as one person.
They live, work, travel, make friends and live a happy life like normal people, and even appear in a reality show on BBC TV. Although many people will go to see them with the curiosity of watching circus programs, they will eventually be moved by their optimism and happiness. For children who attend their classes, they may be regarded as monsters at first, but the school helps children regard them as role models for their happy lives.
Parasitic twins
In 20 17, an American hospital performed an unusual operation on an unusual baby girl Dominic, who was 10 months old. Dominic has two connected spines, a pair of legs, and a bladder on his neck and back. This is the remains of parasitic twins. If these parts are not removed as soon as possible, Dominic will not live for a long time, because these residual limbs will continue to grow, and her small heart and lungs can't support the growth of two bodies, and this extra body will affect the normal development of her body bones.
During the operation, doctors from neurosurgery, plastic surgery, pediatric orthopedics, nephrology and other medical departments gathered together and performed an operation for Dominic for six hours in the operating room, successfully removing the redundant legs and bladder. Dominic recovered well, was discharged five days later, and then grew up normally. But the redundant spine is closely connected with the brain, and it will be very dangerous to remove it. The doctors judged that it would not affect the growth of the child, so they didn't take the risk.
American conjoined twins Owen and emmett were born on 20 13. Their chests are connected, their livers are fused, and they share some intestines and bile ducts. This kind of conjoined twins is more common. 20 14, twins were successfully separated by surgery and grew up happily.
Siamese twins are very rare, about 1 time in 200,000 births. Two babies will be connected in a certain part of the body, often using one or more organs, sometimes enjoying limbs, sometimes enjoying liver, sometimes enjoying heart, and even sharing a head. The degree of physical integration is also large and small.
40% to 60% conjoined babies will die at birth, but some will live to adulthood, most of them are women. Some people think that conjoined twins is caused by incomplete division when the fertilized eggs split into twins, or it may be because the divided fertilized eggs are partially fused after division.
Since ancient times, doctors have tried to separate conjoined babies, but if * * * enjoys important organs, the risk of surgery will be very high. Many operations will lead to the death of twins, and sometimes one of them will be sacrificed.
Parasitic twins are rarer than conjoined twins. In identical twins, one fetus is partially absorbed or stops growing, and the rest is parasitic in the other fetus. Parasitic parts are different, some are parasitic in the brain, and some make healthy babies have more arms and legs. Unlike conjoined twins, this parasitic fetus did not become a living body independently. If it is not taken out from a live baby, it will seriously affect his (her) health.
Sometimes, at the beginning of a mother's pregnancy, there are two fetuses in the uterus. But at the end of pregnancy, one of them disappeared, probably because the fetus had been completely absorbed by another fetus or mother, and finally no parasitic fetus was formed.