Twinning Softchalk

Dizygotic (aka fraternal twins) are more frequent. There is a genetic component to this.

Are monozygotic or dizygotic twins more common?

Dizygotic twins implant separate and develop separate fetal membranes (amnion, chorion, and placenta)

Describe the implantation of dizygotic twins (amnion, chorion, and placenta)

Draw out figure and explain rational.

Draw out this figure.

- 1 zygote and be identical - 2 zygotes and consist of identical twins and a singleton - 3 zygotes and be of the same sex or different sexes

How can triplet form?

Depending on the duration of development, the original embryo may share none, some , or all of their fetal membrane.

How much of the fetal membranes do monozygotic twins maintain?

1-3% of births

How often does twinning occur?

Yes across different populations. It is more frequent in African American populations than in both white and asian populations.

Is there incidence variation in the occurrence of DZ twinning?

Late split bilaminar embryo disc

Mech of twinning: conjoint

Monozygotic, dichorionic diamniotic

Mech of twinning: split at 2 cell stage

Monochorinic, diamniotic

Mech of twinning: split at early blastocyst

Monochorionic, monoamniotic

Mech of twinning: split at late blastocyst

Dizygotic, dichorionic diamniotic

Mech of twinning: two separate zygotes

This shows the pathway of monozygotic vs dizygotic twins

Review

1) in utero death of 1 twin 2) twin twin transfusion syndrome (TTTS) 3) twin reversed arterial perfusion (TRAP sequence) 4) cord entanglement

What are the 4 complications with the anastomosis that can occur during twin pregnancies?

This occurs at the early blastocyst phase. If there is anastomosis of th placental vessels, one two may receive most of thentrution from the placenta and additional blood flow from the other twin. Twin to twin transfusion syndrome.

What can happen between twins if they are monozygotic monochorinonic diamniotic twins?

This figure shows how monozygotic dichorionic diamniotic twins develop from a single zygote.

What does this figure show?

Embryos will have common chorion ad occupy a singe amnion. This makes them monochorionic, monoamniotic twins.

What happens if the splitting occurs after the formation of the blastocyst wit the inner cell mass (late blastocyst stage)? (8-12 days)

The twins will develop separate chorions and amnions. This makes them dichorionic, diamniotic twins. They will behave like dizygotic twins.

What happens if the twinning occurs at the two cell stage of the morula stage (0-4 days)

Occupy the same amnion. However, in some cases the twins may not separate and could end up being conjoined.

What happens if the twins are formed bye splitting of the bilaminar embryonic disc after the primitive streak has started to form? (12-13 days after the primitive streak started to form)

The embryos will share a single chorion ad placenta but occupy separate amnions. Monochorionic, amniotic monozygotic twins.

What happens if they splitting occurs at the early blastocyst stage? (4-8 days)

One twin, the pump twin, provides all the blood flow o the cardiac twin through the plancetal vascular anatomoses. Because of the additional stress on the pump twins heart, the pump twin will likely die. The best approach currently is ablation of the placental anastomosis in utero.

What happens in the case of TRAP sequence?

Monochorionic, monoamniotic twin most commonly experience cord entanglement. Can cause death of one or both and occurs after 20 weeks gestation.

What happens in the case of cord entanglement?

The blood pressure of one twin drops while the remaining is at risk. If one BP fall sharply, the other may suffer heart failure as the heart tries to supply both systems at once. The other twin could also die as a result of a blood clot since they share the same circulation.

What happens in the case of in utero death of one twin?

TTTS occurs in 10-20% of all monochorionic, diamniotic twins. Vascular anastomoses occur between vessels in the 2 placentas that result in unbalanced blood flow between the,. One twin is considered the donor twin. It has oligohydroaminos, growth restriction, and renal insufficiency. The other is the recipient twin that has polyhydroaminos and cardiac enlargement and eventually cardiac failure.

What happens int he case of a twin to twin transfusion syndrome?

Increased risk for chromosomal anomalies and fetal morbidity and mortality are higher in multiple gestations. This also increased the risk of premature births.

What happens with increased multiple gestations vs in single gestations?

Fraternal twins. They arrive from 2 separate oocytes produced during the same menstrual cycle, fertilized by 2 DIFFERENT SPERM.

What is another name for dizygotic twins and how do they arise?

This is how dizygotic twins develop from 2 zygotes. A) when blastocysts implant separately B) when blastocysts come close together In both cases, there are 2 amnions and 2 chorions. Placentas are usually fused when they implant close together.

What is being shown i the following picture?

This figure illustrates how monozygotic, monochorionic, mono amniotic twins and conjoined twins develop. This can occur during the late blastocyst or embryonic disc stages resulting in 2 embryos within one amniotic sac. A) complete division of inner cell mass B and C) incomplete division of disc with partial splitting of the primitive node and steak with various types of twins

What is being shown in this figure?

Most common: Monochorionic, diamniotic twins that occur in the early blastocyst stage. (4-8 days around 65-75%) Least common: Monochorionic, mono amniotic twins (conjoined twins) that occurs in the bilaminar disc stage (12-14 days and less than 1% of the time)

What is the most common type of monozygotic twin? What is the least common?

Monozygotic twins. Also known as identical twins.

What term denotes identical twins?

After 20 weeks.

When are monochorionic mono amniotic twins at risk for umbilical entanglement?

This occurs after day 4. This is important because prior to day 4, all of the cells are totipotent. This means that either zygote can form an entire system. However, after day 4, this is less likely to occur to due cell specialization beginning to take place.

When does specialization of cell begin to occur?

Anywhere from the 2 cell stage to the mural sage. Thus producing identical blastocysts. Each embryo develop its own amniotic and chorionic sacs.

Where can seperation of the blastomeres occur in the development period?