[{"data":1,"prerenderedAt":77},["ShallowReactive",2],{"tool:twins:en":3},{"faq":4,"sources":20,"html":54,"toc":55},[5,8,11,14,17],{"q":6,"a":7},"What is the chance of having twins?","In England and Wales in 2025, 14.3 in every 1,000 maternities were twins, about 1 in 70. The chance is lower for younger mothers and higher in the late thirties, and much higher after some fertility treatments.",{"q":9,"a":10},"Do twins run in families?","Fraternal twins can, through the person who ovulates: a tendency to release two eggs at once can be inherited. Studies found about double the chance for close relatives of mothers of fraternal twins. Identical twins mostly do not run in families.",{"q":12,"a":13},"Does age make twins more likely?","Yes, for fraternal twins. In England and Wales, the twin rate rose from 6.8 per 1,000 maternities under 20 to 17.5 at 40 to 44. Part of the rise at older ages comes from fertility treatment.",{"q":15,"a":16},"How likely are twins with IVF?","With one embryo, about 1 to 3% of births are twins in UK clinics. With two embryos, more than 30% were twins for patients under 35, falling to under 15% after 44. That is why most clinics now transfer one embryo.",{"q":18,"a":19},"Can we do anything to have twins?","There is no reliable way. Diets and supplements have not been shown to work, and fertility clinics aim for one baby at a time, because twin pregnancies carry more risks: at least half of twins are born early and small.",[21,24,27,30,33,36,39,42,45,48,51],{"label":22,"url":23},"Office for National Statistics: Births in England and Wales, birth registrations 2025 (table 7, multiple maternities by age)","https:\u002F\u002Fwww.ons.gov.uk\u002Fpeoplepopulationandcommunity\u002Fbirthsdeathsandmarriages\u002Flivebirths\u002Fdatasets\u002Fbirthsinenglandandwalesbirthregistrations",{"label":25,"url":26},"NHS: Pregnant with twins","https:\u002F\u002Fwww.nhs.uk\u002Fpregnancy\u002Ffinding-out\u002Fpregnant-with-twins\u002F",{"label":28,"url":29},"Monden C, Pison G, Smits J. Twin Peaks: more twinning in humans than ever before. Human Reproduction 2021;36(6):1666-1673","https:\u002F\u002Fpmc.ncbi.nlm.nih.gov\u002Farticles\u002FPMC8129593\u002F",{"label":31,"url":32},"Hoekstra C et al. Dizygotic twinning. Human Reproduction Update 2008;14(1):37-47","https:\u002F\u002Facademic.oup.com\u002Fhumupd\u002Farticle\u002F14\u002F1\u002F37\u002F628856",{"label":34,"url":35},"Lewis CM, Healey SC, Martin NG. Genetic contribution to DZ twinning. American Journal of Medical Genetics 1996;61(3):237-246","https:\u002F\u002Fpubmed.ncbi.nlm.nih.gov\u002F8741868\u002F",{"label":37,"url":38},"Rydhstroem H. Twinning in Sweden between 1973 and 1990: the recurrence rate. Early Human Development 1998;51(1):7-12","https:\u002F\u002Fpubmed.ncbi.nlm.nih.gov\u002F9570026\u002F",{"label":40,"url":41},"Human Fertilisation and Embryology Authority: Multiple births in fertility treatment 2019","https:\u002F\u002Fwww.hfea.gov.uk\u002Fabout-us\u002Fpublications\u002Fresearch-and-data\u002Fmultiple-births-in-fertility-treatment-2019\u002F",{"label":43,"url":44},"Human Fertilisation and Embryology Authority: Risks of fertility treatment","https:\u002F\u002Fwww.hfea.gov.uk\u002Ftreatments\u002Fexplore-all-treatments\u002Frisks-of-fertility-treatment\u002F",{"label":46,"url":47},"Smeenk J, Wyns C et al. ART in Europe, 2020: results generated from European registries by ESHRE. Human Reproduction 2025;40(11):2038-2055","https:\u002F\u002Fpubmed.ncbi.nlm.nih.gov\u002F40985526\u002F",{"label":49,"url":50},"Legro RS et al. Letrozole versus clomiphene for infertility in the polycystic ovary syndrome. New England Journal of Medicine 2014;371(2):119-129","https:\u002F\u002Fpubmed.ncbi.nlm.nih.gov\u002F25006718\u002F",{"label":52,"url":53},"Diamond MP et al. Letrozole, gonadotropin, or clomiphene for unexplained infertility. New England Journal of Medicine 2015;373(13):1230-1240","https:\u002F\u002Fpubmed.ncbi.nlm.nih.gov\u002F26398071\u002F","\u003Ch2 id=\"how-the-calculator-works\">How the calculator works\u003C\u002Fh2>\n\u003Cp>For a natural pregnancy, the calculator starts from real births: how many maternities in England and Wales were twins in 2025, for each age group of the mother, from the Office for National Statistics. Across all ages it was 14.3 in every 1,000, about 1 in 70.\u003C\u002Fp>\n\u003Cp>It then splits that figure in two. Identical twins happen at about the same rate everywhere and at every age, about 4 in every 1,000 births, which the NHS puts as about 1 in 250. Everything above that is fraternal twins, and that is the part that changes with age and with family history.\u003C\u002Fp>\n\u003Cp>If you tick that fraternal twins run in the family of the person who ovulates, or that you have had twins before, the calculator doubles the fraternal part. It does not double it twice when both are true, because both point to the same tendency.\u003C\u002Fp>\n\u003Ch2 id=\"identical-and-fraternal-twins\">Identical and fraternal twins\u003C\u002Fh2>\n\u003Cp>\u003Cstrong>Identical twins\u003C\u002Fstrong> come from one fertilised egg that splits in two. They share the same genes and are always the same sex. Why an egg splits is not well understood, and it seems to happen mostly by chance.\u003C\u002Fp>\n\u003Cp>\u003Cstrong>Fraternal twins\u003C\u002Fstrong>, also called non-identical twins, come from two eggs released in the same cycle and fertilised separately. They are no more alike than any other brothers and sisters, and can be a boy and a girl. According to the NHS, about one in three twin pairs is identical and two in three are fraternal.\u003C\u002Fp>\n\u003Ch2 id=\"why-age-matters\">Why age matters\u003C\u002Fh2>\n\u003Cp>Releasing two eggs in one cycle becomes more common as people get older, up to the late thirties. In England and Wales in 2025, the twin rate was 6.8 per 1,000 maternities under 20, 12.2 at 25 to 29, 14.7 at 30 to 34 and 17.0 at 35 to 39. A review of research on fraternal twins describes a fourfold rise from age 15 to 35.\u003C\u002Fp>\n\u003Cp>These national figures include pregnancies after fertility treatment, which become more common after 35. For a natural pregnancy at 35 to 44, the calculator's figure may therefore be a little high. At 45 and over, most twin births follow egg donation or IVF, so the calculator does not give a natural estimate.\u003C\u002Fp>\n\u003Ch2 id=\"twins-in-the-family\">Twins in the family\u003C\u002Fh2>\n\u003Cp>A tendency to release more than one egg can be inherited, and it matters on the side of the person who ovulates. In a large Australian twin register, sisters of mothers of fraternal twins had 1.7 times the usual chance, and daughters of female fraternal twins 2.5 times. Older studies found about twice the chance for mothers and daughters. Twins in the partner's family do not change the chance for this pregnancy.\u003C\u002Fp>\n\u003Cp>Having had fraternal twins before points the same way: a Swedish study found the chance of twins again in a later birth was two to three times higher. Identical twins mostly do not run in families. Our \u003Ca href=\"\u002Fguides\u002Fdo-twins-run-in-families\">guide to twins in the family\u003C\u002Fa> goes into more detail.\u003C\u002Fp>\n\u003Ch2 id=\"twins-after-fertility-treatment\">Twins after fertility treatment\u003C\u002Fh2>\n\u003Cp>Fertility treatment changes the picture so much that the calculator shows its own figures instead of adjusting the natural ones:\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Cstrong>IVF with one embryo:\u003C\u002Fstrong> about 1 to 3% of births are twins in UK clinics. Twins only come if the embryo splits.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>IVF with two embryos:\u003C\u002Fstrong> over 30% of births were twins for patients under 35 in UK clinics, falling with age to under 15% after 44.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Insemination (IUI):\u003C\u002Fstrong> in Europe, about 8% of births with a partner's sperm and about 6% with donor sperm were twins.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Ovulation tablets\u003C\u002Fstrong> such as clomiphene or letrozole: 3% to 13% of pregnancies were twins in two large trials.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Ovulation injections\u003C\u002Fstrong> (gonadotropins): in a large trial, 32% of pregnancies were twins or triplets.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>Your clinic knows your own treatment and can give you a more precise figure.\u003C\u002Fp>\n\u003Ch2 id=\"what-the-calculator-leaves-out\">What the calculator leaves out\u003C\u002Fh2>\n\u003Cp>Some studies link taller height, a higher BMI or having had several children to a slightly higher chance of fraternal twins, but the results are small or inconsistent, so the calculator does not use them. Diet, supplements and the timing of conception have no proven effect. The country you live in matters a little: twin rates are similar across western Europe, between about 14 and 16 per 1,000 maternities.\u003C\u002Fp>\n\u003Ch2 id=\"if-you-are-expecting-twins\">If you are expecting twins\u003C\u002Fh2>\n\u003Cp>Twins usually show up at the first scan, around 12 weeks, which also shows whether the babies share a placenta. A twin pregnancy needs closer care, because twins are more often born early and small. Your midwife or doctor will explain what that means for you. The \u003Ca href=\"\u002Ftools\u002Fdue-date-calculator\">due date calculator\u003C\u002Fa> still works as a starting point, though twins often arrive before the due date.\u003C\u002Fp>\n\u003Cp>And if you are simply curious what two little faces of yours might look like, the \u003Ca href=\"\u002Ftwins-generator\">twins generator\u003C\u002Fa> makes a picture of two possible children from a photo of each of you, just for fun.\u003C\u002Fp>\n",[56,59,62,65,68,71,74],{"id":57,"text":58},"how-the-calculator-works","How the calculator works",{"id":60,"text":61},"identical-and-fraternal-twins","Identical and fraternal twins",{"id":63,"text":64},"why-age-matters","Why age matters",{"id":66,"text":67},"twins-in-the-family","Twins in the family",{"id":69,"text":70},"twins-after-fertility-treatment","Twins after fertility treatment",{"id":72,"text":73},"what-the-calculator-leaves-out","What the calculator leaves out",{"id":75,"text":76},"if-you-are-expecting-twins","If you are expecting twins",1793362217902]