Dichorionic twins are a form of multiple gestation in which each twin has a separate placenta (blood supply) and amniotic sac. Dichorionic twins are usually–but not always –fraternal (non-identical).
Di-di twins
Both identical and fraternal twins can be di-di, or dichorionic-diamniotic, though all fraternal pairs are of this type. Di-di twins each have their own placentas and amniotic sacs, sharing only the womb to develop.
Approximately 10% of Di/Di twins will be monozygotic, resulting from the early splitting (within the first 3 days) of a single embryo. Both fetuses will have arisen from the same egg and sperm, and therefore, will be genetically identical (and have the same sex as confirmed by ultrasound).
Sometimes health care professionals identify same-sex twins as fraternal or identical based on ultrasound findings or by examining the membranes at the time of delivery. The best way to determine if twins are identical or fraternal is by examining each child's DNA.
While identical twins will always be the same gender, di-di fraternal twins can go either way. You can end up with girl-girl twins, boy-boy twins, or boy-girl twins. In fact, science has found that the most common type of fraternal twins is boy-girl!
Monochorionic-monoamniotic twins are identical twins that share both a placenta and an amniotic sac. This is the rarest and highest risk form of twin pregnancies.
Barring pregnancies that result from assisted reproductive technology, dizygotic twins are far more common than monozygotic twins and account for 70 percent of all twin gestations.
A little more than half of twin pregnancies end in preterm delivery (before 37 weeks). While 40 weeks is the full gestation period of the average pregnancy, most twin pregnancies are delivered at approximately 36 weeks (range 32-38 weeks depending on the type of twin pregnancy).
Di-Di twins: with complications such as discordant growth, high risk of preterm delivery, discordant fetal anomalies. Mo-Di twins: with concern for congenital anomalies, unequal placental sharing, discordant growth, TTTS.
Mo-Mo twins should always be delivered by cesarean section to avoid umbilical cord complications for the non-presenting twin at the time of the first twin's delivery. A woman carrying Di-Di or Mo-Di twins is a good candidate for a vaginal birth if: The presenting twin is in a vertex position.
To form identical or monozygotic twins, one fertilised egg (ovum) splits and develops into two babies with exactly the same genetic information. To form fraternal or dizygotic twins, two eggs (ova) are fertilised by two sperm and produce two genetically unique children.
#1 Fraternal twins can be conceived as much as 24 days apart
For this reason, fraternal twins can be conceived a few weeks apart, though they generally will be born at the same time.
Finally, this outcome allowed us to detect a case of dizygotic twins with different fathers, which is a rare and infrequent event reported in the literature. This case reiterates the need for the participation of both twins in paternity testing as these events happen although their frequency is not high.
By 32 weeks, each twin weighs about 1.7kg (3.7lb) (Cole et al 2011, Zhang et al 2015) and measures about 42cm (16.5in) from head to foot (crown to heel) (Cole et al 2011). One twin may be bigger than the other (Leombroni et al 2016). Your babies' bodies are now in proportion to their heads (Moore et al 2019).
Odds of Having Another Set of Multiples
The National Organization of Mothers of Twins Clubs claims that once you have had fraternal (dizygotic) twins, your chances of having another set are three to four times greater than that of the general population. Both hereditary and environmental factors may contribute to this.
DCDA pregnancies account for the majority (~76%) of all twin pregnancies. They account for all dizygotic pregnancies and ~20% of monozygotic pregnancies.
If we consider all births, we estimate that identical twins with Down syndrome occur at the rate of 1 or 2 in a million pregnancies and non-identical twins at the rate of 14/15 in a million.
Dichorionic twins are a form of multiple gestation in which each twin has a separate placenta (blood supply) and amniotic sac. Dichorionic twins are usually–but not always –fraternal (non-identical).
The first wife (died ante 1770), of Feodor Vassilyev (b. 1707–c. 1782), a peasant from Shuya, Russia, gave birth to 16 sets of twins.
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. It sounds like fraternal twins do indeed run in your family!
Caesarean section and twins
In the UK, more than half of twins and almost all triplets are delivered by caesarean section is a common method used during twin and triplet births.
This research supports the role of genetics in aggression as the twins that were genetically identical, i.e. 100% of the same genes, were more likely to display criminal behaviour than the twins that only shared 50% of the same genes.
Identical twins share the same genomes and are always of the same sex. In contrast, fraternal (dizygotic) twins result from the fertilization of two separate eggs with two different sperm during the same pregnancy. They share half of their genomes, just like any other siblings.