Monoamniotic-monochorionic Twins These types of twins share a chorion, placenta, and an amniotic sac. This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords.
But there are many other, less common, twin subtypes. These include conjoined twins, superfetation, heteropaternal superfecundation, polar body twins, semi-identical twins, and mirror-image twins.
One placenta and one amniotic sac.
This is the riskiest and rarest type of twin pregnancy. Fetal complications can arise due to tangling of the umbilical cords or an imbalance in nutrients, blood or other vital life supporting systems.
There are two types of twins – identical (monozygotic) and fraternal (dizygotic). To form identical twins, one fertilised egg (ovum) splits and develops two babies with exactly the same genetic information.
Dizygotic twins are the most common type and are known as fraternal twins. Two-thirds of all sets of twins are dizygotic. When two eggs are fertilized during the same pregnancy, the result is a set of dizygotic twins. They are fertilized by two different sperm.
– Decuplets: a combination of 10 of a kind. In this case, babies! A South African woman has reportedly given birth to 10 babies at once, besting a world record set just last month.
However, for a given pregnancy, only the mother's genetics matter. Fraternal twins happen when two eggs are simultaneously fertilized instead of just one. A father's genes can't make a woman release two eggs.
Once the babies are large enough to stay in one position in the womb, the twin lowest in the uterus is known as Baby A and the one furthest from there is Baby B, according to the Stanford Medicine News Center. In the majority of vaginal births, Baby A is born first.
There are more than just fraternal and identical twosomes; other rare twin types include “half identical twins” (when the egg splits and then each half is fertilized) and mirror image twins (identical twins who develop asymmetrically). 3. Identical twins don't have identical fingerprints.
Superfetation is when a second, new pregnancy occurs during an initial pregnancy. Another ovum (egg) is fertilized by sperm and implanted in the womb days or weeks later than the first one. Babies born from superfetation are often considered twins since they may be born during the same birth on the same day.
Twins not only have a bestie from birth — they also live longer than singletons. And those two factors may be related, according to new University of Washington research.
Rare Diagnosis: "MoMo" Twins
Dr. Refuerzo performed another ultrasound and diagnosed monochorionic-monoamniotic (“MoMo” or “Mono Mono”) twins, which are incredibly rare, comprising about 1 in 10,000 births and only about 1 percent of identical twin pregnancies.
“Having twins is not twice as hard—it's exponentially more difficult,” says Natalie Diaz, author of What To Do When You're Having Two and CEO of Twiniversity, a global support network for parents of twins.
The notion that twins always skip a generation is also a myth. The illusion may have arisen because men who inherit the gene from their mothers are unaffected by it ( they do not ovulate), but can still pass it on to their daughters, who, in turn, will have an increased likelihood of conceiving twins.
The term mirror twin is used to describe a type of identical, or monozygotic, twin pairing in which the twins are matched as if they're looking into a mirror — with defining characteristics like birthmarks, dominant hands, or other features on opposite sides.
Septuplets (7)
The Frustaci septuplets (born 21 May 1985, in Orange, California) are the first septuplets to be born in the United States. Born at 28 weeks, only two boys and one girl survived; one daughter was stillborn and three died within 19 days of birth.
According to The American Society for Reproductive Medicine, women who are fraternal twins have a 1 in 60 chance of having twins, and men who are fraternal twins have a 1 in 125 chance of fathering twins. It was previously believed that identical (monozygotic) twins were random — not genetic.
According to the Guinness World Records, the longest interval between the birth of twins is 90 days. 5 The former record was 87 days apart for two sisters born in 2012—who, ironically, were born in Waterford, Ireland.
Twins on the average seem to have lower IQs than singletons. The best estimate for this group difference is 4.2 IQ points (less than one-third of a standard deviation), with a great divide between study outcomes of less vs more recent birth cohorts (5.1 vs 0.5 IQ points, respectively).
The longest interval between the birth of twins is 90 days, in the case of Molly and Benjamin West, dizygotic (fraternal) twins born in Baltimore, Maryland, USA to parents Lesa and David West (all USA) on 1 January and 30 March 1996.
It's impossible for these types of twins to have different fathers. However, fraternal twins – when two separate eggs are fertilized by two separate sperm – can look different from one another. Only about 19 heteropaternal superfecundation cases worldwide have been reported to date.
They come from the same fertilized egg and share the same genetic blueprint. To a standard DNA test, they are indistinguishable. But any forensics expert will tell you that there is at least one surefire way to tell them apart: identical twins do not have matching fingerprints.
But you may be left wondering: Can twins have different fathers? The answer is yes, but only in cases in which they're fraternal, as identical twins form from a single egg/sperm combination and thus cannot have different fathers.
In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.