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.
Mirror-image twins is an unofficial phenomenon that occurs among identical twins almost 25 percent of the time, according to Dr. Nancy Segal, a psychologist and director of the Twin Studies Center at California State University, Fullerton.
'Mirror image' is a type of identical twinning. It can happen in any type of identical twins. When the split occurs late - more than a week after conception - the twins can develop reverse asymmetric features. This term is not really a type of twin, just a way to describe their physical features.
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.
Mirror syndrome or triple edema or Ballantyne syndrome is a rare disorder affecting pregnant individuals. It describes the unusual association of fetal and placental hydrops with maternal preeclampsia.
Some studies suggest that mirror twins may even hold opposite personality traits. Psychological mirroring can affect everything from their social-emotional development and temperament to career interests, and possibly even sexual orientation.
Generally, identical twins can only be of the same gender. However, rare cases, such as sesquizygotic (semi-identical) twinning may cause identical twins to be a boy and a girl.
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.
Dizygotic (DZ) twins, also called fraternal twins, occur when two egg cells are each fertilized by a different sperm cell in the same menstrual cycle. DZ twins are about twice as common as MZ twins, and they are much more likely to run in families.
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.
Yes, mirror twins share the same genetic makeup, but their fingerprints are not identical. No one's fingerprints in the world are the same. Mirror image twins would have similar fingerprints, but they'd be the opposite pattern, in the same way twins' birthmarks or cowlicks may mirror each other.
In some extreme cases (which are exceptionally rare), mirror twins display situs inversus. In this condition, the internal organs (such as the heart, liver, lungs, or stomach) are situated on the opposite side of the normal anatomical position.
Is there a third type? Traditionally, the science around twins has taught that identical and fraternal are the only two types. But a third type might exist, called polar body or half-identical twins.
The phenomena — which occurs in approximately 25 percent of all identical twins, according to Laura Segal, PhD, director of the Twin Studies Center at California State University, Fullerton — is common but relatively unknown.
While many people can't tell them apart, Mary-Kate and Ashley are not identical, but rather fraternal: Mary-Kate is one inch taller than her sister and is left-handed, while Ashley is right-handed. (Ashley is two minutes older too, FYI.) 2.
These twins are called fraternal twins, dizygotic twins (meaning two zygotes) or non-identical twins. During pregnancy, the developing babies get oxygen and food from their mother through the placentas and umbilical cords. Fraternal twins have separate placentas and umbilical cords.
For a given pregnancy, the odds of conceiving fraternal twins are only determined by the mother's genetics, not the father's. Fraternal twins happen when two eggs are simultaneously fertilised instead of just one.
Many people believe twins skip a generation, but that's just a myth. The idea that twins skip generations likely comes from the fact that the genetic factors contributing to twins only come from the gestational parent's side.
Most often, fetuses known in utero as twin A are also first born and thus retain their label. However, this is not always the case, such that the twin A newborn was previously labeled twin B in utero and vice versa.
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).
As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood.
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.
If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA.
This is a very rare birth of twins—a boy and a girl—from a single fresh compaction-morula produced by ICSI. We had to examine why there were two babies of different sex, which meant that it was a dizygotic twin pregnancy.
Polar body twinning is thought to occur when an egg splits - and each half is fertilised by a different sperm. This results in twins who appear very much alike but share approximately 75% of their DNA.