The reason why the egg splits is unknown – but the main theory has been that the process happens randomly. This is unlike the process whereby non-identical twins develop as a result of two separate eggs being fertilised by two sperm – a process that runs in families, unlike “monozygotic twinning”, researchers said.
Although the root cause for this is still unknown, we do know that during an IVF transfer, the blastocyst, or developing embryo, can collapse in on itself. When this happens, sometimes it can cause the inner cell mass to split into two. The two inner cell masses lead to the development of twins.
Splitting of the embryo may occur at any time during the first 2 weeks after fertilization, resulting in several forms of monozygotic twins.
"Embryo splitting occurs approximately in one out of 100 embryo transfers," Grifo said. "The chance of this outcome is approximately one in 10,000. This could also occur in a natural conception, but the chance of that is much [rarer].
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.
Factors that could increase the risk of zygotic splitting, which results in multiple embryos in the womb, include using frozen-thawed embryos, maturing the fertilized egg in the lab for five or six days before implantation, and assisted hatching — a process where clinicians create a small hole in the layer of proteins ...
Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families. But there are some factors that make having non-identical twins more likely: non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese.
Superfetation is when a second, new pregnancy occurs during an initial pregnancy. Another ovum (egg) is fertilized by sperm and implanted in the womb days or weeks later than the first one. Babies born from superfetation are often considered twins since they may be born during the same birth on the same day.
In the context of assisted reproduction treatments, the procedures of embryo splitting potentially provide the opportunity to gain a higher number of embryos by dividing one embryo, which increases the chance of successful nidation and therefore the overall likelihood of a pregnancy.
There are 3 types of identical twins. About one-third of identical twins split soon after fertilisation and form completely separate twins. Like fraternal twins, these twins have separate placentas. The other two-thirds split after they attach to the wall of the womb.
An obvious way to reduce this high twin rate would be to transfer only one embryo. This would require that cryopreservation of the supernumerary embryos be efficacious enough so that the chance of achieving an ongoing pregnancy is not diminished by transferring a single embryo in the stimulated cycle.
Elevated Beta-hCG Levels
If you are using a regular pregnancy test (not the super-sensitive variety) and get an immediate positive (especially a very dark positive indicator) a few days before your period is due, there may be an increased chance that you are carrying twins.
While any fetus at 5 weeks is still tiny, ultrasounds can still find the gestational sacs in the uterus, meaning it's possible to find out you have twins this early!
It is estimated that 1 in 250 natural pregnancies will naturally result in twins. While twin pregnancies can happen by chance, there are some factors that may increase your odds of having two babies at the same time. Let's learn about twins!
In the majority of vaginal births, Baby A is born first. But occasionally the twins switch positions at the last minute, and Baby B emerges first, as further noted by the Stanford Medicine News Center. Still, the birth order is relatively straightforward.
No. Only one ovulation can happen per cycle. You can, however, ovulate two (or more) eggs at the same time. When this happens, there is the potential to conceive fraternal (non-identical) twins if both eggs are fertilized.
Polar twins. Polar twins share the same chromosomes from their birthing parent, but they get different chromosomes from their non-birthing parent. This is because they're created from a single egg but two separate sperm.
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.
The quick answer to this question is that, in a twin pregnancy, it is the mother's genes that determine twins. First up, giving birth to identical twins is not genetic, but conceiving fraternal twins is. The mother may have the genetic trait of releasing two eggs in one menstrual cycle.
Identical twins are completely random. It's not based on family history or genetics. Identical twins form when a single fertilized egg splits and forms two embryos. Now in this case, it's not because of mom or dad.
A straight answer is: yes. Obviously, the blastocyst can split: day 3 embryos evolving into day 5 embryos can split. However, if we transfer two embryos and then you get a twin pregnancy, this is dizygotic. So they are not sharing the same placenta because they are different – and we know that we have put two embryos.
Embryo transfer is arguably the most critical step in the IVF process. On the surface, it seems like a relatively simple procedure. The embryos are loaded in a catheter and the physician deposits them through the cervical canal into the uterine cavity.
The main reason for the seemingly higher occurrence rate of twins through IVF is the practice of transferring more than one embryo at a time in an IVF cycle. Until recently, most fertility doctors routinely transferred multiple embryos in the hope of achieving a better chance of success.
In a twin pregnancy, there are elevated levels of hCG, making it possible to have a very early positive result. However, home pregnancy tests won't confirm if twins are present, only the presence of hCG. It takes around 2 weeks after conception for hCG to be detected in a hCG pregnancy test.