In di/di twins, each twin has their own placenta and their own amniotic sacThe amniotic sac, also called the bag of waters or the membranes, is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo (and later fetus) until shortly before birth.https://en.wikipedia.org › wiki › Amniotic_sac
Monochorionic Diamniotic Twin Gestations
By definition, twins of a monochorionic pregnancy are of the same gender and share a single placenta (see Figs. 160.1 and 160.2).
Identical twins are almost always the same sex, although there are some rare exceptions to this rule. Because identical twins occur when a single fertilized egg splits and forms two embryos, each embryo has the same chromosomes (usually, XX for girls or XY for boys). Remember that sex and gender are not the same.
In a di/di pregnancy (more scientifically referred to as a dichorionic diamniotic pregnancy) the twins each have their own chorionic and amniotic sacs. Essentially, each of the babies is growing like they would as a singleton, but just a little more cramped, because they're sharing the same womb.
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.
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.
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).
A twin pregnancy with two placentas and two amniotic sacs is the optimal twin pregnancy, as each baby has its own nutritional source and protective membrane.
While your babies are small, a DNA test is the most accurate way of finding out (MBF 2016, NHS 2022a). The test is called twins DNA testing or zygosity testing. It establishes whether your twins are identical (monozygotic) or fraternal (dizygotic).
In addition to the risks that all twin pregnancies face, mono/di pregnancies are at risk for complications related to a shared blood supply inside the placenta. Circulatory imbalances can result in twin-twin transfusion syndrome (TTTS).
Twins who share the same placenta, where the first baby is positioned head-down, can be safely delivered vaginally. The new data analysis of monochorionic twins, which are identical twins who share the same placenta, shows vaginal birth is safe for both the mother and her babies between 32 and 38 weeks of pregnancy.
Although identical twins have the same genes, they don't always look the same. This is because children's health and development are shaped not only by genes but also by experiences in the womb and after birth. For example, a twin who gets less blood from a shared placenta might weigh less at birth.
Risk assessment by ultrasound scan in the first and early second trimester identifies a subgroup of monochorionic twins with a more than 70% risk of a complicated outcome and a survival rate of only 69%.
Are Di-Di Twins Usually the Same Gender? 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!
What are monochorionic, diamniotic twins? Monochorionic, diamniotic (MCDA) twins are the product of a single fertilized ovum (egg), resulting in genetically identical offspring. MCDA twins share a single placenta (blood supply) but have separate amniotic sacs.
In effect, though identical twins don't have identical DNA, they are genetically similar.
For this reason, fraternal twins can be conceived a few weeks apart, though they generally will be born at the same time.
Do Identical Twins Run in Families? Identical twins are typically not hereditary like fraternal twins and occur in three to four births out of every 1,000 globally. A few families report a higher level of identical twins than expected, so there may be a genetic factor in rare cases.
When more than one ovum is fertilized and implants in the uterus, the result is dizygotic (fraternal) twins, triplets, or other multiples. Although two fetuses develop simultaneously in superfetation, they differ in maturity, having been conceived days or even weeks apart.
Age. According to the Office on Women's Health , women who are aged 30 years or older are more likely to conceive twins. The reason for this is that women of this age are more likely than younger women to release more than one egg during their reproductive cycle.
For women born 1870-1899, moms of twins averaged reproductive spans of 14 years 11 months versus 14 years for singleton moms. Both results were statistically significant. Moms of twins also were older at the time of their last birth.
People over 30, and particularly those over age 35, are more likely to conceive twins. 4 This is because the level of follicle-stimulating hormone (FSH) rises as birthing parents get older. FSH is responsible for the development of eggs in the ovaries before they are released.
Because fraternal, or dizygotic, twins are 2 separate fertilized eggs, they usually develop 2 separate amniotic sacs, placentas, and supporting structures. Identical, or monozygotic, twins may or may not share the same amniotic sac, depending on how early the single fertilized egg divides into 2.
More than half of twins and other multiples are born early, before 37 weeks of pregnancy, so there's a 50/50 chance that yours will arrive before their due date too. Many twins are born between 35 and 37 weeks.
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.