The exact mechanism of fertilization could not be determined but the study stated that it was unlikely to be a case of polar body twinning.In 2019, a second case of sesquizygotic twins was reported and molecular evidence of the phenomenon was documented by Gabbett and Fisk. In this case, the twins shared 100% of their maternal chromosomes and 78% of their paternal genomic information. The authors postulate two sperm from the same man fertilized an ovum simultaneously. The chromosomes assorted themselves through heterogonesis to form three cell lines. The purely paternal cell line died out due to genomic imprinting lethality, while the other two cell lines, each conisiting of the same maternal DNA but only 50% identical paternal DNA, formed a morula which subsequently split into twins

Mirror image twins
Mirror image twins result when a fertilized egg splits later in the embryonic stage than normal timing, around day 9–12. This type of twinning could exhibit characteristics with reversed asymmetry, such as opposite dominant handedness, dental structure, or even organs (situs inversus). If the split occurs later than this time period, the twins risk being conjoined. There is no DNA-based zygosity test that can determine if twins are indeed mirror image. The term "mirror image" is used because the twins, when facing each other, appear as matching reflections. Language development
There have been many studies highlighting the development of language in twins compared to single-born children.
More than half of twins are born weighing less than 5.5 pounds (2.5 kg), while the average birth weight of a healthy baby should be around 6–8 pounds (3–4 kg). This is largely due to the fact that twins are typically born premature. Premature birth and low birth weights, especially when under 3.5 pounds (1.6 kg), can increase the risk of several health-related issues, such as vision and hearing loss, mental disabilities, and cerebral palsy. There is an increased possibility of potential complications as the birth weight of the baby decreases. Twin-to-twin transfusion syndrome
Monozygotic twins who share a placenta can develop twin-to-twin transfusion syndrome. This condition means that blood from one twin is being diverted into the other twin. One twin, the donor twin, is small and anemic, the other, the recipient twin, is large and polycythemic. The lives of both twins are endangered by this condition. Stillbirths
Stillbirths occurs when a fetus dies after 20 weeks of gestation. There are two types of stillbirth, including intrauterine death and intrapartum death. Intrauterine death occurs when a baby dies during late pregnancy. Intrapartum death, which is more common, occurs when a baby dies while the mother is giving birth. The cause of stillbirth is often unknown, but the rate of babies who are stillborn is higher in twins and multiple births. Caesareans or inductions are advised after 38 weeks of pregnancy for twins, because the risk of stillbirth increases after this time.