fraternal or identical and what exactly does that mean
Since it’s been visable from the very beginning that my babies are diamniotic (each in their own amniotic sac), combined with my age, the feeling among the doctors is that I am probably having fraternal twins. If I find out I’m having a boy and a girl then that will be confirmed before birth. If they are the same sex, we’ll have to wait for genetic tests done on the placenta(s) after the births to be sure.
Here is some information to help some of that make more sense:
(from various websites)
“Depending on the stage at which the zygote divides, identical twins may share the same amnion (in which case they are known as monoamniotic) or not (diamniotic) [amnion=amniotic sac]. Diamniotic identical twins may share the same placenta (known as monochorionic) or not (dichorionic). All monoamniotic twins are monochorionic. Also note that any monochorionic or monoamniotic twins are identical twins. This condition does not occur in fraternal twins.”
“Pregnancies that develop from one egg can share some placental vessels. Whether the babies share vessels depends on the time when the egg divides. This is called the babies’ placentation, or chorionicity.
Eggs dividing from the time of ovulation to day three after ovulation are completely separate and share nothing other than common genetic material. They are known as diamniotic-dichorionic (Di-Di). The amnion and chorion are the two layers of your bag of water that fuse together. Diamniotic dichorionic means each baby has its own amnion and chorion. (They are each in separate sacs.) Since there are two babies, the pregnancy contains two amnions and two chorions; thus, the term di, or two, is placed in front of the words amnion and chorion. These twins do not share any vessels
Eggs that split three to eight days after ovulation create diamniotic-monochorionic twins. Two-thirds of twins developed from a single egg are this type. In this case, each baby has its own amnion (diamnionic) but share a single chorion (monochorionic) meaning that each baby has its own placenta but share some vessels. These twins are at risk for twin-to-twin transfusion syndrome.
Eggs that divide day eight to thirteen after ovulation live in the same bag of water, have one placenta, and share a single amnion and a single chorion, and are called monoamnionic-monochorionic (Mo-Mo) twins. Since they share the same swimming area, these babies have a very high risk for dying due to
cord entanglement. Less than 2 percent of twin pregnancies from a single egg are monoamnionic-monochorionic.
Eggs that split day thirteen to eighteen result in conjoined twins (Siamese twins). This problem is extremely rare: 1 in 50,000 to 80,000 deliveries. Whether the twins can be separated after birth depends on the organs and body parts that are shared.”
“Fraternal twins (commonly known as “non-identical twins”) occur when two fertilized eggs are implanted in the uterine wall at about the same time, within the same menstrual cycle, or in rare cases within one menstrual cycle of each other. The two eggs form two zygotes, and these twins are therefore also known as dizygotic.
Dizygotic twins are no more similar genetically than any siblings and develop in separate amnions, with separate placentae. They may have different genders or the same gender. However, twins of differing genders are almost always fraternal.”
So you have 6 ways to designate twins:
are they two eggs = dizygote
or are they one egg that split = monozygote
are they sharing the same amniotic sac = monoamnionic
are they in different sacs = diamnionic
are they sharing the same placenta = monochorionic
are they in different placentas = dichorionic
The biggest reason to know if your twins are sharing the sac or the placenta is because of the health risks that can occur during the pregnancy. There are problems that can occur when they share vessels that can result in the death of one or both twins.
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