What Causes Twin Pregnancy

Nature has designed the human body to nurture and give birth to one young one at a time. There are exceptions to this rule is multiple births when twins, triplets, or even octuplets are conceived and are born.  The average duration of twin pregnancies is 36 weeks.  A weight gain of about 35 to 45 pounds is recommended for twin pregnancies.

Twin conceptions occur in one of two ways:

1. When a single egg is fertilized by sperm but in due course and splits, each half developing into a twin, it is a case of identical twins. Identical twins share the same gestational sac and placenta. Identical twins are of the same look and sex mostly. In medical terms, these are called monozygotic twins.
2. When more than one egg is released and fertilized at the same time, fraternal twins are conceived. Fraternal twins have separate placentas and gestational sacs. Fraternal twins may be of different sexes. These are called dizygotic twins.

What causes twins?

1. Heredity is found to play a major role in twin births. If either of the parent’s families has a history of twins, the likelihood of having twins increases. Twins and multiple pregnancies tend to run in families
2. Older women have a higher than average chance of conceiving twins. Medical research shows that women in the age group 35-39 years have a 20 percent chance of conceiving twin
3. The use of fertility drugs in assisted reproduction techniques increases the woman’s rate of ovulation and also increases the chance of multiple conceptions.
4. Racial factors also influence the probability of twin pregnancies- research has found that incidence of naturally conceived twins among Nigerians and Africans in general and lowest among Japanese.
5. Research shows that twins are common in women with a body mass index of over 30 and women of above-average height.
6. A woman who has had children earlier has a higher probability of having twins in subsequent pregnancies. 
7. Older women are also more likely to have twins or multiple pregnancies.
8. The diet of a woman also increases the possibility of conceiving twins. A diet rich in dairy products and cassava causes hyper ovulation i.e. release of one egg per cycle. 
9. Research shows that a woman who conceives while breastfeeding an older child is 9 times more likely to conceive twins.
10. In IVF treatments, more than one fertilized egg is transplanted in the uterus. This is done to increase the possibility of at least 1 embryo surviving till full gestation. Sometimes, all the embryos survive and thrive, resulting in multiple pregnancies. This is considered the major cause of the increase in twin births in recent times.
11. In certain cases, having twins is an act of fate.

As per current figures, one in 80 births is that of twins. The incidence of naturally occurring twin pregnancies is highest in the African race and lowest among the oriental race.