Editing Multiple birth (section)

===Twins===
{{Main|Twin}}
Twins are by far the most common form of multiple births in humans. The U.S. [[Centers for Disease Control and Prevention]] report more than 132,000 sets of twins out of 3.9 million births of all kinds each year, about 3.4%, or 1 in 30.<ref name="Cohn-2015" />  Compared to other multiple births, twin births account for 97% of them in the US.<ref>{{Citation |last1=Gill |first1=Prabhcharan |title=Twin Births |date=2023 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK493200/ |access-date=2023-12-10 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29630252 |last2=Lende |first2=Michelle N. |last3=Van Hook |first3=James W.}}</ref> Without fertility treatments, the probability is about 1 in 60; with fertility treatments, it can be as high as 20-25%.<ref>{{Cite web |title=Twin Statistics - What is your chance of having twins? |url=http://www.keepkidshealthy.com/twins/twin_statistics.html |archive-url=https://web.archive.org/web/20080207015248/http://www.keepkidshealthy.com/twins/twin_statistics.html |archive-date=7 February 2008 |access-date=13 May 2016 |publisher=keepkidshealthy.com}}</ref>

Dizygotic (fraternal) twins can be caused by a hyperovulation gene in the mother.<ref>{{Cite web |title=Is the probability of having twins determined by genetics?: MedlinePlus Genetics |url=https://medlineplus.gov/genetics/understanding/traits/twins/ |access-date=2021-04-06 |website=medlineplus.gov |language=en}}</ref> Although the father's genes do not influence the woman's chances of having twins, he could influence his children's chances of having twins by passing on a copy of the hyperovulation gene to them.

Monozygotic (identical) twins do not run in families. The twinning is random, due to the egg splitting, so all parents have an equal chance of conceiving identical twins.<ref>{{Cite web |last=Bellefonds |first=Colleen |title=Do Twins Really Run in Families? |url=https://www.whattoexpect.com/pregnancy/twins-and-multiples/do-twins-really-run-in-families/ |access-date=10 February 2019 |website=What to Expect}}</ref>