I have also heard that IVF and other non-intercourse related methods can do this. IE you can ask the IVF clinic to split the eggs before insertion?
How soon do you know from a natural birth too? Can one increase their chance? Certain foods?
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First of all, just to be clear: IVF-associated twinning and “tripletting” are most commonly of the dizygotic (“fraternal”) variety. You appear to be asking about monozygotic (“identical”) twinning given the reference to “splitting the egg.” I will provide a brief overview of both.
Types of multiple conceptions and relationship to IVF
Dizygotic ("fraternal") twins (and higher multiples) occur because more than one egg is fertilized. This is very common during the in vitro process because the ovaries are stimulated using medications, as opposed to the normal menstrual cycle where usually only one egg is release. Because multiple birth pregnancies have considerably higher rates of both maternal and fetal complications,1 IVF centers and mothers together have to make a decision weighing the risk of multiple embryo transfer with the benefits of improved probability of successful live birth. In some countries, there are laws against transferring more than one embryo, but in the United States this varies by center, and overall about 35 percent of IVF pregnancies are twins, with 7-8 % being triplets.2
Monozygotic ("identical") twins occur because an early embryo divides after fertilization. This results in two embryos with identical DNA (hence the terminology and phenotype - “identical”). These have also been shown to be more common in IVF pregnancies, although the degree of over-representation is considerably less marked compared to the situation with dizygotes. The mechanism is also less clear.
Is this desirable?
Monozygotic twins (and higher multiples) have markedly increased rates of every pattern of fetal and perinatal mortality, overall between four and seven times the rate compared to singletons.3 This may be in part due to the fact that the process of splitting is itself a “deformity” of sorts that tends to cluster with other deformities. It is also the case that monozygotic multiple births at times share, to varies degrees, portions of the placental sac (mono-chorionic and at times also mono-amniotic). Mono-amniotic are susceptible to umbilical cord entanglement, which can lead to serious complications. Those that do not share an amniotic sac (mono-chorionic, di-amniotic) are susceptible to something called Twin-twin Transfusion Syndrome wherein blood is shunted from one twin to the other via vascular connections between the placentas. This can lead to severe anemia of the “donor” twin and polycythemia (overload of red blood cells) in the “recipient”, both of which carry complications.3
can (we) ask the IVF clinic to split the eggs before insertion?
Your goal appears to to increase the chance of monozygotic twinning. Although it has been shown3 that certain factors do increase this chance (advanced maternal age and some technical considerations during the fertilization step), because of the above considerations about complications during monozygotic multiple embryo pregnancies, this is considered an undesirable outcome during IVF. As such, IVF centers are unlikely to do anything likely to increase this chance.
Seoud MA, Toner JP, Kruithoff C, Muasher SJ. Outcome of twin, triplet, and quadruplet in vitro fertilization pregnancies: the Norfolk experience. Fertil Steril. 1992 Apr;57(4):825-34.
Abusheikha N, Salha O, Sharma V, Brinsden P. Hum Reprod Update. Monozygotic twinning and IVF/ICSI treatment: a report of 11 cases and review of literature. 2000 Jul-Aug;6(4):396-403.