While some women wish to have twins, the thought of caring for two babies at the same time is scary to others.
Have you ever wondered how the little ones are conceived?
Well, first we need to understand that there are two types of twins; identical and non-identical.
Identical twins occur when one egg is fertilised by a single sperm to form one zygote (fertilised egg), hence the name monozygotic twins. The zygote then splits into two separate embryos.
The two embryos later develop into fetuses sharing the same womb (uterus).
This type of twins, which is half as common as non-identical ones, have the same genes and are thus the same sex, but differ in behaviour and environmental influences.
The twins may share a placenta in the uterus depending on the stage at which the zygote divides. Occasionally, they also share an amniotic sac.
Twins are more likely to share structures when twinning occurs at a later stage in the pregnancy (4-12 days after fertilisation).
However, when twinning occurs 12 days after fertilisation, it is likely to result in conjoined twins.
Fraternal twins, commonly referred to as non-identical twins, occur when two eggs are released at ovulation, with each egg being fertilised by its own sperm cell, producing two genetically unique children.
The twins, scientifically known as dizygotic, don’t share the same mix of genes, thus can be of different sex.
Although studies show that non-identical twins run in the family, only the female has any influence on the chances of having fraternal twins, as the male cannot make her release more than one egg.
This is dependent on the woman carrying a fraternal twin gene and can also be affected by heredity, race, marital age and number of children previously born.
Two-thirds of all twin births result in same sex fraternal twins, with one-third being different sex fraternal twins.
Sources:
Familyeducation.com
Betterhealth.vic.gov.au
Twinsuk.co.uk