Twins are two offsprings produced by the same pregnancy. There are two types of twins: monozygotic and dizygotic. Monozygotic twins occur at a rate of three in every 1000 deliveries worldwide. But in dizygotic twinning occurrence is about 6 per 1000 birth in Japan which is 4-5 to 15 per 1000 in identical twins in India. Monozygotic or identical twins are formed when our egg is fertilized by one sperm. A zygote is formed which then divides into two separate embryos. Dizygotic twins are formed when two separate sperms fertilize. Two separate eggs hence form two zygotes. This is also called bio-cellular or fractal twins. This is the most common type of twins.
Monozygotic twins share the same placenta. Each shares the same genetic component and identical genetic structures. Dizygotic twins like any other siblings have an extremely small chance of having the same chromosomal profile. Even if they have a same chromosomal profile, they will always have different genetic material on each chromosome. These twins may look similar but mostly they look different from each other.
Predisposing factors that can cause Twin Pregnancies:
- Advanced maternal age
- Fertility drugs
- ART: in IVF or ART women have taken fertility drugs
- Familial: if you have highest twins in your family then there are more chances of twins yourself
- African and American women have more chances of having twins
- Multiparity: Women who have two or more kids before having more chances of having twins
- Women who have twins prior. The chances of having twins again is higher
- When women are on the pill after stopping the pill try to conceive straight
- When women have more BMI. Then also there are chances of having twins>30
- Mothers who are twins are more likely to have twin babies. There is no influence on the male partner’s side
- Women who keep breastfeeding the older baby or toddler have more chances of having twins
Complication of Twins Pregnancies:
- Vanishing Twins: In this pregnancy, in the starting, there is two fetuses but slowly one of the fetuses does not grow and it decreases in size and vanish. The single fetus goes to term.
- Carry Out Twins: These twins are monozygotic twins whose body joined together during pregnancy. This occurs when the zygote splits after day 12 following fertilization and fails to separate completely. This occurs in 1 in 50000 human pregnancies.
- Parasitic Twins: Sometimes one twin fails to develop completely and carry problem for the surviving twins.
- Partial Molar Twins: A very rare type of parasitic twins where single usable twins are endangered. When other zygotes become cancerous or molar.