Twinning
Twinning means that two babies are born as a result of one pregnancy. Born babies can be identical (monozygotic) or non-identical (dizygotic, fraternal). Identical twins happen when a single egg cell is fertilized by a single sperm sell and then this fertilized embryo splits into two. Non-identical twins happen when two separate egg cells are fertilized by two sperm cells. The reason for multiple births is complex, both genetic and environmental factors can affect.
In Genetics Home Reference: Is the probability of having twins determined by genetics?
[PMID 27406421] Two SNPs Associated With Spontaneous Dizygotic Twinning: Effect Sizes and How We Communicate Them.
[PMID 27132594
] Identification of Common Genetic Variants Influencing Spontaneous Dizygotic Twinning and Female Fertility.
[PMID 25882505] Women who deliver twins are more likely to smoke and have high frequencies of specific SNPs: Results from a sample of African-American women who delivered preterm, low birth weight babies.
