During pregnancy twins are made and formed when one fertilized egg (ovum) splits and develops into two babies with exactly the same genetic information and to form fraternal or dizygotic twins, two eggs (ova) are fertilized by two sperm and produce two genetically unique children.
Conception of babies happen when a sperm fertilizes an egg to form an embryo.
However, if there are two eggs present in the womb at the time of fertilization or the fertilized egg splits into two separate embryos, a woman can become pregnant with twins.
Twins do sometimes fight in the womb as it's been shown on some ultrasounds of twin pregnancies that twins have been kicking each other, punching each other and it shows to be that the twins are boxing each other in the mothers womb.
Twins do see each other and interact with each other in the womb once they have eyes and can see somewhat.
Twins have even been seen cuddling each other in the womb on an ultrasound so they are aware of each other when in the womb.
Mothers of twins do typically live longer than mothers who only give birth to one baby at a time.
Although having twins does not mean you'll live longer but you have a higher chance of living longer when you have twins as opposed to just having one baby.
The reason it is bad to have twins is because there can be more complications when carrying twins and birthing twins than there is with just carrying or birthing one baby.
However there's nothing you can do to prevent twins and once you have twins you have to birth them regardless.
Mothers with twin pregnancies are more likely to have pregnancy health problems and complications like gestational diabetes, pre-eclampsia, premature labor and bleeding.
Twins are rare.
Having twins is a rare thing to happen during pregnancy but it's not as rare as having multiples or triplets or more.
Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families.
But there are some factors that make having non-identical twins more likely: non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese.
It is estimated that 1 in 250 natural pregnancies will naturally result in twins.
While twin pregnancies can happen by chance, there are some factors that may increase your odds of having two babies at the same time.
The rarest type of twins are Monoamniotic-monochorionic Twins as these types of twins share a chorion, placenta, and an amniotic sac.
This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords.
In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.
And women who are fraternal twins have a 1 in 60 chance of having twins, and men who are fraternal twins have a 1 in 125 chance of fathering twins.