There are two types of twins: identical and non-identical. In identical twins, the babies come from one ovum fertilized by a sperm cell. This fertilized ovum will then split into two or more cells resulting in two fetuses that have similar DNA, blood type and physical characteristics such as complexion and hair and eye color. Their gender is also usually the same. Identical twins usually share the same placenta yet grow in different amniotic sacs.
Meanwhile, non-identical twins (also known as fraternal twins) develop from two different ova and sperm cells, do not share a placenta or amniotic sac, and their faces are not as similar as identical twins’ appearances. Their blood type and gender can be similar or different.
Nobody knows exactly why a pregnancy is able to produce twins, especially identical ones. All women actually have similar chances of becoming pregnant with identical twins. The odds of having identical twins are one in 350-400 pregnancies. The likelihood of having identical twins is usually neither inherited nor influenced by age and ethnicity.
Fraternal twins are more common than identical twins. Here are some factors that can influence the birth of fraternal twins.
– Ethnicity: Fraternal twins usually occur more in certain ethnicities. The occurrence of fraternal twins is most common among African people, with Japanese the rarest. In Western Europe, twins happen in one of every 60 pregnancies, while in Nigeria twins are seen once in 20-30 pregnancies. Nevertheless, Nigerians who live outside their country have a lower likelihood of bearing twins, so the fact that African people have a higher chance of twins is suspected to be linked to diet and environmental factors.
– Age: Although giving birth to twins has its risks, should you get pregnant over the age of 35, you have a higher chance of bearing twins. That is because as you get older, you tend to release more than one ovum when ovulating.
– Hereditary factors: Fraternal twins can be descended from the mother’s side. Fraternal twins, who are caused by two ova — a woman’s ability to produce more than one ovum when ovulating — tend to be an inherited trait. As a result, if a would-be mother has a mother or grandmother who is a fraternal twin, the odds of having fraternal twins is higher.
– Previous children: Although not yet scientifically proven, if you have previously had children, you could have a greater chance of having twins. This means your reproductive system works well and ovulation is not problematic, so the possibility of producing more than one ovum when ovulating is higher. Alternatively, if you have delivered twins before, it does not mean that your next pregnancy will also be twins.
– IVF: In vitro fertilization is a technique used to help those who are diagnosed as infertile or have problems with their reproductive system. When undergoing IVF, usually more than one embryo is implanted into the uterus to increase success rates, and more than one embryo is able to grow into a fetus afterward. This causes twin pregnancies for many of those who undergo IVF. According to NHS Choices, one twin pregnancy occurs in 80 pregnancies in normal fertilization. However, with IVF, the chance of twins is a ratio of one in five. (kes)