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.
The term “MZ twins” simply means that the twins came from the same zygote. Using that definition, the answer is yes! In extremely rare cases, MZ twins that began as a male zygote have developed into a male/female twin pair!
In humans, twins can result either from the ovulation and fertilization of two oocytes with the outcome of dizygotic twins (DZT) or from the splitting of a single embryo at some stage of its early development, resulting in monozygotic twins (MZT).
Can an embryo split into twins? The short answer is yes, but the chances are quite small. Just like with any pregnancy, a twin pregnancy can still happen. In IVF, the chance of this outcome is approximately one out of 100 transfers.
Non-identical (dizygotic) twins happen when 2 separate eggs are fertilised and then implant into the womb (uterus). These non-identical twins are no more alike than any other 2 siblings. Non-identical twins are more common. The babies may be of the same sex or different sexes.
Blastocyst stage (days 4–8) division results in monochorionic-diamniotic twins. Division at the 8–12-day stage results in monochorionic-monoamniotic twins, and division after day 12 leads to conjoined twins [1, 2].
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).
Just a few years ago, scientists discovered a pair of fraternal, or non-identical twins, that actually shared a placenta! It happened in Seattle, and was discovered by the New England Journal of medicine. It's worth pointing out that the chances of this happening are so small as to be vanishingly unlikely.
Monochorionic diamniotic twin pregnancies have a more hazardous intrauterine stay than their dichorionic counterparts because of the vascular anastomoses that connect the two fetal circulations. The survival of monochorionic twins diagnosed in the first trimester is 89%.
You are 3- 6% more likely to have a baby boy than a girl when using IVF to conceive. IVF increases the odds of a boy from 51 in 100 when conceived naturally to 56 in 100 with IVF.
A single embryo transfer may still result in twins because of embryo “splitting”. There is about a 1.6% chance of identical twins arising naturally after a single embryo transfer.
Can an embryo split after 6 weeks? What about having twins happen after your first-trimester scan? It's very unlikely, as most twin embryos split within the first 2 weeks of fertilization.
Monoamniotic-monochorionic Twins
This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords. If you have monoamniotic-monochorionic twins, your healthcare provider will monitor your pregnancy closely.
Identical twins turn out as the same gender about 99.9% of the time.
The Science of Fraternal Twins. Mixed-gender twins are the most common type of fraternals, some 50 percent are boy-girl. To understand this combination: Males have XY chromosomes, females have XX chromosomes.
Monozygotic twinning (MZT) occurs when an embryo splits after fertilization, resulting in identical twins.
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.
1 As the fertilized egg (called a zygote) travels to the uterus, the cells divide and grow into a blastocyst. In the case of monozygotic twins, the blastocyst then splits and develops into two embryos. In contrast, dizygotic (fraternal) twins form when two separate eggs are released and fertilized by two sperm.
Embryo splitting
They will be clones of each other, but not genetically identical to either of the parents. The disadvantages associates with embryo splitting are: We cannot predict the specific traits of the clones (as the embryos contain a mixture of DNA from both parents). It has a low success rate.
If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA. A boy has XY chromosomes and a girl has XX chromosomes. Girl-boy twins occur when one X egg is fertilized with an X sperm, and a Y sperm fertilizes the other X egg.
The prevalence of true zygotic splitting was 1.36%, and the researchers found that, compared to singleton pregnancies, using frozen-thawed embryos increased the risk of zygotic splitting embryos by 34%, maturing the blastocysts in the lab for a few days before embryo transfer increased the risk by 79%, and assisted ...
Fraternal Twins: This type of twin set is the most common. This occurs when two different eggs are both fertilized by two different sperm and implant themselves into the uterine wall at the same time.
While many cases may progress well until the third trimester, pregnancy loss may be as high as 50% due cardiac failure of the normal twin, also called “pump twin”, and complications related with polyhydramnios. The survival rates with cord occlusion range 80%–90%.
Twins can change positions, but if they're head-down at 28 weeks, they're likely to stay that way. When delivering twins vaginally, there is a risk that the second twin will change position after the delivery of the first. Research shows that second twins change positions in 20 percent of planned vaginal deliveries.