Fascinating Facts About Twins

There are a lot of interesting myths, rumors and questions surrounding the phenomenon known as twins. Let’s sort out the facts from the fiction:

Which Women Are Most Likely to Conceive Twins Naturally?


First, women of “advanced maternal age” (as my doctor labeled me unflatteringly) are more likely to conceive twins. As they get closer to menopause (after age thirty-five), they begin to ovulate more irregularly. Therefore, the chances of releasing more than one egg in a given menstrual cycle are higher. For some reason, as well, if women already have children, they’re more likely to have twins. In fact, the probability of having twins is three times higher in women over the age of thirty-five with at least four other children than for women under twenty who are pregnant for the first time. In addition, African-American women have a 1 in 79 chance of conceiving twins; Caucasian women have 1 chance out of a hundred; and Asian women conceive twins more rarely—1 in 155 pregnancies. Finally, when women first stop taking the birth-control pill, their pituitary glands kick in with higher amounts of stimulation than usual, so the chance of conceiving twins is greater in the first month off the pill.


What Are Polar Body Twins?

Polar body twinning occurs when a woman releases one unfertilized egg, it splits in two, and then each is fertilized by two different sperm. The resulting children have the same genes from their mother, but different genes from their father, so they are essentially “half-identical.”


What Is Vanishing Twin Syndrome?


Because the diagnosis of twins is happening earlier in pregnancy thanks to the use of ultrasound, doctors are discovering more cases of Vanishing Twin Syndrome (VTS). This occurs when twins are initially conceived, but one mysteriously disappears during pregnancy, resulting in a singleton pregnancy. In other words, one twin is miscarried; the other survives. The miscarried twin’s fetal tissue is usually absorbed by the mother, the placenta or the other twin. This condition most often occurs in the first trimester, so many VTS cases go undetected if an ultrasound is not performed in the first three months of pregnancy. Some estimates say that 1 in 8 people may have started as a twin, but only 1 in 70 pregnancies actually result in a twin birth. This usually poses no physical problems for the mother or surviving child, but there is often an emotional component whereby parents grieve over losing a child but are relieved that one has survived.


Do Twins Have a Special Language?


Just like married couples, your twins spend so much time together that they may develop particular “code words” that they use to communicate. For instance, if one calls his blanket a “bubby,” the other may soon follow suit. But this tendency, called “idioglossia” or “cryptophasia,” can’t be classified as a separate language. Just like singletons, when twins first start talking, they have trouble pronouncing certain words. As they pick up each other’s habits of saying things, they develop their own “secret code.” But as their speaking skills improve, the “twin language” will disappear.


Are More Twins Born During a Particular Season?


Surprisingly, the answer is yes! In areas that experience long summer days, such as the northern parts of Japan and Finland, more fraternal twins are conceived in the month of July. It’s theorized that the weather causes increased levels of the follicle stimulating hormone (FSH) in women, which affects the number of eggs that are released each month. So, if you want a second set of twins, schedule your next vacation in northern Japan in July!

Do Identical Twins Have the Same Fingerprints?


It’s not clear why, but identical twins have different fingerprints! This often comes in handy when parents take their identical twins home from the hospital and remove their hospital bracelets. If they can’t tell the twins apart, they can be fingerprinted again and matched with the prints taken at the hospital.


Do Twins Skip a Generation?


There is no scientific proof that giving birth to twins skips a generation. Of course, it sometimes happens, but twins can just as easily be conceived in every generation of a family, or once and never again! However, women in a particular family can have a genetic predisposition for producing more than one egg during a menstrual cycle, therefore making them more likely to have twins. This is why it sometimes seems that “twins run in the family.” Note that since these twins are the result of multiple eggs being fertilized, this “genetic component” only holds true for fraternal twins.


Is There Always a “Good Twin” and a “Bad Twin”?

Of course not! Like any two siblings, your twins are going to have differences in personality or go through different developmental stages. One may go through a stage where he’s sweet as molasses, while the other one makes you want to tear your hair out! But beware, just as you’ve slapped the “good” or “bad” labels on your twins, they’re likely to go through a new stage in which they’ll swap roles. All children have challenging periods of development. Unfortunately (or is it fortunately?), twins usually pick different times to do so.


Are Conjoined Twins More Common Among Certain Ethnic Groups?

Conjoined twins (also known as Siamese twins) are a form of monozygotic (identical) twins, and they occur at the same rate throughout the world. No one really knows why an egg splits (whether completely or not, as in the case of conjoined twins), and this phenomenon doesn’t seem to be affected by maternal age, ethnicity, heredity, hormonal treatments or any other factors that can result in fraternal twins. For some reason, though, conjoined twins are more likely to be female, but again the reasons are unknown. Are more female conjoined twins actually conceived, or is it just that more of them actually survive? Scientists are still examining this issue.


What Are Mirror-Image Twins?

Mirror-image twins are identical twins that result from the splitting of the fertilized egg late in the embryonic stage. About twenty-five percent of identical twins are classified as “mirror-image,” and of the 6.3 billion people in the world, only 5 million are mirror-image twins. How do you know if you’re looking at mirror-image twins? Well, if you have them face each other, certain traits will match up as if one was looking into a mirror. For example, their cowlicks may match (one on the left side of the head; one on the right side), or one may be left-handed and the other right-handed.

Adapted from It’s Twins! Parent-to-Parent Advice from Infancy Through Adolescence (Hampton Roads, March 2007). Copyright ©2007 by Susan M. Heim.

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About Susan Heim

Susan M. Heim is an author and editor, specializing in multiples, parenting, women’s and Christian issues. Her books include "Boosting Your Baby's Brain Power"; "Chicken Soup for the Soul: Twins and More"; "It’s Twins! Parent-to-Parent Advice from Infancy Through Adolescence"; "Twice the Love: Stories of Inspiration for Families with Twins, Multiples and Singletons"; and, "Oh, Baby! 7 Ways a Baby Will Change Your Life the First Year." Upcoming books include "Chicken Soup for the Soul: All in the Family," "Chicken Soup for the Soul: Devotional Stories for Women," and "Moms of Multiples' Devotions to Go." Susan's articles and essays have appeared in many books, magazines and Web sites. She is a member of the National Association of Women Writers and the Southeastern Writers Association, and has a degree in Business Administration from Michigan State University. Susan lives with her husband and four sons (two teenagers and twin grade-schoolers) in Florida.

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  1. susan brosnan says:

    i really enjoyed your letters they were very helpful as my daughter is pregnant with her 3 child and her husband is a twin and her nana had twins and her uncle had twins so just wondered what were her chances of having twins. Thank You.

  2. Jolene Myers says:

    I found this stuff very interesting!!! I have a really interesting story myself and I am actually searchin the internet to see how rare my families situation is. My mother is an identical twin, she then had me and my sister who are also identical (mirror image) twins then I in turn had a set of identical twins. All three sets identical twin girls. Crazy I know so anyone with any info on how common or uncommon this is please let me know

    • Julie Smith says:

      My mother is an identical twin and she had idential twin girls. I know they say it isn’t genetic, but it sure seems like it!

  3. Susan Heim says:

    Hi Jolene,
    I don’t have statistics on this either, but I know that identical twins “running” in families is very rare. The birth of identical twins is normally considered a random event (unlike with fraternal twins, where a woman may inherit the tendency to ovulate more than one egg in a cycle), so your case is definitely unusual! It would be interesting to find out if there could be an inherited tendency for eggs to split into identical twins.

  4. samantha thomson says:

    does anyone have info. on the theroy that invitro fertilization may increase your chances of having identical twins. if you do please let me know very interested!!!!!

  5. I have been reading a lot on polar body twins because I am often asked if my twins are identical or not. In all the articles I have read, I have never read that polar body twins have to have different fathers. Actually I would think that that would be very rare, and I think this definition is far too narrow. If my twins are polar body, then I have polar body twins from the same father. It is more likely that my egg split and was fertilized by two of my husband’s sperm- not two different men. I’m not saying that that never happens,but I think this author needs to do some more research, at least on polar body twinning.

  6. you have one bit of information wrong. Polar body twins do not have to be from different men. They usually have the same father.

  7. Susan Heim says:

    Dan and Melisa, thanks so much for pointing out that polar body twins can and usually do have the same father. I just corrected the definition in the article. I appreciate your expertise!

  8. I have polar body twins. When I was first pregnant, one embryo was much smaller than the other and seemed to be “empty”. I was told to excpect a miscarriage. Two weeks later, the smaller embryo was larger and had a heart beat. It took a long time for the small one to catch up in size. I delivered at 29 weeks, so a lot of testing was done, including genetic. I was told my babies were polar body twins!! A boy and a girl! They look A LOT a like, but they are of different sex. I believe the Olsen twins fall in this category as well.

  9. Thank u for the information. I have 2month old mirror image twin girls. Their hair parts on opposite sides and their birth marks are on opposite sides of their bellies. I can’t wait to see if one is right handed and one left handed!

  10. Dan

    She never indicated that polar body twins come from different father’s. She stated that they recieve different genes from the father, and the exact same from the mother. Although the ones you thought she was speaking of do exsist. I have polar body twins. It was explained to me that my egg spilt before fertilization causing the egg to have identical genetics from myself. The egg was then fertilized by Dad with two seperate sperm resulting in different genetics from him. The results are half identical and half fraternal. They are girl/boy twins that look extremely identical except for the fact they are of different sex. Hope tis helps!

  11. Its Amazing how that works. I have one set of frat twins and got pregnant with another set of frat twins. Why is it an increased chances after you have a set of twins??

  12. Hi Toria! I don’t really know for sure, but I’m guessing that if a woman has quite a few children, it’s just an indication that she’s very fertile. And if she’s fertile, she’s more likely to be a “super-ovulator,” which means she may release more than one egg during a monthly cycle, which can result in twins.

  13. Interesting article! I didn’t know that, “It’s theorized that the weather causes increased levels of the follicle stimulating hormone (FSH) in women”. I guess if your insurance doesn’t cover IFV you could take a trip to Japan or Finland in July :)

  14. Debbie Marks says:

    My son is doing a class project on twins and he is a identical mirror image twin, we are having fun with this project, i just made him and his brother come into the room and face each other to show them why they are mirror image. they are 18 year old now and it’s sure been fun, lots of work but fun, From the very day we found out we was having twins we read everything we could get our hands on to understand how this twin thing come about hehehehe, soon fear set in, could we carry them to term, i left my job, took medication , and had to great doctor and lots of prayer and we made it , i had read something somewhere that identical twins was conceived in may and ours was ( if anyone wants to have twins)

  15. OMG that was so hopeful! i think im going to get a good grade on my school project!! -thanks