Twins can be formed in several ways during pregnancy:
1. Fraternal Twins: Fraternal twins occur when two separate eggs are fertilized by two separate sperm. This happens when a woman releases two eggs during her menstrual cycle, and both eggs are fertilized by sperm. Fraternal twins can be of the same or different genders and genetically resemble siblings born at different times.
2. Identical Twins: Identical twins occur when a single fertilized egg (zygote) splits into two separate embryos. This usually occurs within the first few days after fertilization. Identical twins share the same genetic material and are usually of the same gender. They will have a similar physical appearance and may have some identical characteristics.
3. Semi-Identical Twins: Semi-identical twins, also known as sesquizygotic twins, are an extremely rare type of twins. It occurs when a single egg is fertilized by two sperm, resulting in three sets of chromosomes (usually two from the father and one from the mother). This type of twinning has only been reported a few times.
4. Polar Body Twins: Polar body twinning is an extremely rare phenomenon that occurs when an egg splits before or after fertilization. This results in two embryos with different genetic material. However, both embryos come from the same mother as they are derived from the same egg.
It is important to note that the type of twinning depends on various factors, including genetics, maternal age, fertility treatments, and other factors that may increase the likelihood of multiple pregnancies.
how can twins are formed during pregnancy
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