Different Types of Twins

Updated on May 10, 2017

4D Ultrasound of Fraternal Twins

Twins at 17 weeks gestational age
Twins at 17 weeks gestational age

Two Types of Twins

Fraternal twins, also known as dizygotic twins, are the most common type of twins. They can be boy/girl, girl/girl or boy/boy. Boy/girl twins are the most common type of fraternal twins.

Identical twins, also known as monozygotic twins, are a more rare occurrence. Identical twins are always the same sex; either boy/boy or girl/girl.

Fraternal Twins

Fraternal twins result from the mother hyper-ovulating, releasing more than one egg during her menstruation cycle. A woman can inherit a gene, from either of her parents, which causes her to hyper-ovulate. Fertility treatments can also cause hyper-ovulation. When two eggs become fertilized by two individual sperm cells, fraternal twins result. Each twin has its own amniotic sac and its own placenta. When the two fertilized eggs implant close to one another, their placentas are so close, they fuse together, appearing to be one placenta. The placentas fusing together into one, when fraternal twins are of the same sex, can cause them to be mistaken as identical twins.

Many siblings, who are not twins, greatly resemble one another; however, some siblings don't look very similar to each other at all. The same goes with fraternal twins. In fact, they may look so much alike that some people may even mistake them for being identical twins ( Mary Kate and Ashley Olsen are said to actually be fraternal twins) or they may look so different that people question if they are siblings at all. Fraternal twins are basically siblings in the womb at the same time. Other than sharing the same pregnancy together, fraternal twins are no different than any other siblings.

Types of Fraternal Twins

  • Sororal Twins - Fraternal twins that are girl/girl twins are referred to as 'sororal twins and are the most rare form of fraternal twins.
  • Superfetation- This is when twins are conceived at different times due to the mother releasing an egg that gets fertilized while she is already pregnant.
  • Heteropaternal Superfecundation-Disturbing but true- when a woman releases more than one egg during ovulation and two become fertilized by two different men, resulting in twins who have different fathers
  • Tetragametic Chimerism- This occurs when one zygote of a set of fraternal twins absorbs the other zygote and combine into one. It will now be one person with two separate sets of DNA.

Identical Twins

Identical twins are formed from one egg that has been fertilized by one sperm and then, spontaneously, splits in half, forming two eggs. They share the exact same DNA with each other. Identical twins may or may not share a placenta and amniotic sac depending on when the egg splits. If the egg splits within the first two days, they will each have their own placenta and their own amniotic sacs. If the egg splits between three to eight days, it most likely will result in two separate sacs but sharing of the same placenta. If the egg splits thirteen days after conception, they will share the same placenta and amniotic sac. When identical twins share both a placenta and amniotic sac, there is a higher risk of complications and mortality. Identical twins that do share a placenta can develop what is called, twin to twin transfusion syndrome. Twin to twin transfusion syndrome is where blood from one twin (the donor twin) is passed to the other twin (the recipient twin). The recipient twin is large and has a large number of red blood cells in his/her circulatory system. The donor twin is small and sickly. This condition endangers the lives of both twins. If the egg doesn't split until even later, conjoined, or Siamese, twins result.

Fraternal Newborn Twins Sleeping

Surprising Facts About Twins

Types of Identical Twins

  • Mirror Image Twins: Only identical twins can be mirror-image twins. This occurs when the egg takes longer than usual to split, usually a week or longer after conception.The original right half of the egg becomes one individual and the original left half becomes the other. These twins are mirror images of each other. If one has a mole on their left cheek, the other will have a mole on their right cheek. If one's hair parts on the right, the other's parts on the left. In rare cases, one twin will have all their internal organs on the opposite side of the body.

  • Polar Body Twins: Polar body twins are very uncommon. They are half-identical twins. This happens before fertilization. The egg divides unevenly. The smaller half (known as the polar body) normally would dissolve and be reabsorbed into the mothers body. However, in polar body twinning, instead of dissolving or dying off, it remains and acts as a second egg. Then there are two identical eggs and they are fertilized by two separate sperm from the father. Therefore, the DNA from the eggs is identical and the DNA from the separate sperms is not.

  • Conjoined Twins: Conjoined twins, or Siamese twins, occur when the egg splits very late and not completely.

Twins Born with Different Dads

Twin Pregnancy

Twin pregnancies are on the rise. This is partly due to the increased amount of women undergoing fertility treatments, and to the fact that many women are waiting until their late 30's or older to have children. According to a report from the National Center for Health Statistics, part of the Centers for Disease Control and Prevention, twin pregnancy's have risen 76% between 1980 and 2009.

All twin pregnancies are considered "high risk" pregnancies. Twin pregnancies are very stressful and demanding on a woman's body, especially an older woman's body. Twin pregnancy symptoms are much more pronounced and twin pregnancies are much more apt to have complications such as, hospital bed-rest, preeclampsia, HEELP syndrome (Hemolytic anemia, Elevated Liver enzymes, and a Low Platelet count), and PIH (Pregnancy Induced Hypertension) , just to name a few. They are also much more likely to have to have an early delivery, which may result in the preemie twins having to stay awhile in the NICU (Neonatal Intensive Care Unit). A mother with a twin pregnancy may be more likely to need to deliver her babies with a cesarean section, as one baby may be breech and the other head down. Even if both babies are head down, after the first is delivered, the other may flip, causing the need for a C-section. So, some twin births are delivered both vaginally and cesarean section. Mothers of twins also require more recovery time after giving birth.

Mary-Kate and Ashley Claim to Be Fraternal Twins

Mariah Carey
Celine Dion
Jennifer Lopez
Angelina Jolie
Nancy Grace
Rebecca Romijn
Marcia Cross
Julia Roberts
Julie Bowen
Lisa Marie Presley
Jane Seymour

Ways To Increase Chances For Twin Pregnancy

  • If you have a family history of twins (fraternal), your chances of conceiving twins is higher.
  • Older women, 35+ have more of a chance having twins than a younger woman.
  • Women that consume high amounts of dairy are said to have more of a chance getting pregnant with twins.
  • If you are breastfeeding and become pregnant, your chances of a twin pregnancy is higher.
  • Chances of having twins increases with each pregnancy.
  • African women have the highest odds of conceiving twins, followed by European women. Hispanics and Asian women have the lowest odds.

Herbs That Increase Chances For Twin Pregnancy

Speak to your healthcare provider before taking supplements.

  • Maca Root
  • Evening primrose oil
  • Flaxseed oil
  • Licorice
  • Vitex
  • Sweet Cassava
  • Black Cohosh
  • Pineapple Core

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.


    0 of 8192 characters used
    Post Comment
    • liataylor profile imageAUTHOR


      3 years ago

      Thank you for commenting, Catherine. Superfetation is common in many animals, but an extremely rare occurrence in humans. I believe there are only 11 cases documented. The last was in 2015. Conception can be days to weeks apart. The biggest age difference so far has been two months. I think they've all been delivered at the same time, like twins. Although I guess, being different ages, they aren't technically twins.

    • CatherineGiordano profile image

      Catherine Giordano 

      3 years ago from Orlando Florida

      An excellent article about twins. I learned a lot about twins. In superfetation is the second twin conceived within days of the first month or is it a month or two later. If there is a gap of a month or mor are they both born at the same time?


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, wehavekids.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://maven.io/company/pages/privacy

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
    ClickscoThis is a data management platform studying reader behavior (Privacy Policy)