Updated: 2018, Sep 29

Twin Pregnancy: How Twins are Formed? Know its Types & Complications

By - Reviewed by CHD Team
Twin Pregnancy

Thanks to fertility treatments, multiple births have become more common in the recent years. It is also observed that more and more women are trying to conceive in their later years, which also contributes to higher chance of having twins. Mother can suspect that they have twins if twins run in their family, they have had fertility treatment, or they seem bigger than they should be. Earliest they can find out if they have twins or not is the ultrasound scan, scheduled between week 8 and week 14.

What Causes Twins?

Chances for twins are 1 in 340 to 400. There is no 100% theory of what causes twins, but there are some factors that contribute to such. One of them is the In vitro fertilization (IVF) which increases the odds. Other factors are ethnic groups (African Americans have higher chance for twins), age (older mothers have higher chances for twins), and gender (non identical twins run on the mother’s side).

How Twins are formed?

Twins are formed a bit differently than ordinary babies. Single babies are formed when the egg is fertilized by a single sperm, and the egg cell divides in the next days. With dividing, the egg cells form a structure called blastocyst, which later forms the embryo. Identical twins also start from a single egg, fertilized by a single sperm. But, unlike single babies, the egg will split in two separate embryos. The split happens within the first week, and the day it happens determines what they will share in the uterus (amnion, placenta and chorion). The earlier the egg splits, the more independent eggs will be. Non identical twins are formed from two fertilized eggs from two different sperm cells. Embryos develop separately, each having its own placenta, amnion and chorion.

How Twin Pregnancy is Different?

Not a single pregnancy is the same, but there are some significant differences between normal and twin pregnancy. For starters, more fatigue and morning sickness is normal. Mothers are making two placentas, and they should expect double sickness and fatigue. Exercise is important, even a single walk is enough in normal pregnancy, but when it comes to twins, things are different. Rest is more important here, and mothers should try to rest as much as possible. There will be time for exercise. All the risks are increased. Visits to the doctor’s office should be more frequent, in order to keep track of everything. Mothers that carry twins should drink a lot more water than mothers that carry just one baby. Also, more vitamins are required.

Different Types of Twins

There are three different types of twins: identical, non-identical and super twins. Approx. 33% of twins are identical, while 60% are non-identical.

  • Identical twins are formed from a single, fertilized egg, which is then divided in two, thus creating two babies with same genes. They are always same sex, and they look alike. Sometimes, they can have separate placenta, and this happens when the egg splits before implanting.
  • Unlike identical, non-identical twins are formed from two, separate eggs. They are more common, and sometimes they don’t even look alike. Non-identical twins can be both same sex and different sex.
  • Super twins are multiple twins. The term is used for three, four, five or more twins. There is also a different term to identify the number of twins: triplets (3 babies), quadruplets (4 babies), quintuplets (five babies) and so on. Chances for triplets are 1 in 8,500 births, for quadruplets 1 in 600,000 births and for quintuplets 1 in 50,000,000 births.

Complications of Twin Pregnancy

There are always risks of complications with pregnancy, but with twins, they are increased. One of the common complications is high blood pressure (two to three times more likely than in normal pregnancy). Pre-eclampsia is also three times more likely to happen with twins. Chances for diabetes are two to three times higher to boot. Some others complications that may occur with twin pregnancy are anemia (due to increased blood flow), obstetric cholestatis and itching.

Special Care During Twin Pregnancy

Since twin pregnancy is a lot different from normal pregnancy, even more special care is needed in order to prepare the mother for childbirth, and to ensure health of the babies. Nutrition is essential for proper growth, and the intake of calories is different from normal pregnancy. More calories are now required, and mothers should try to eat several small meals. Visits to the physician should be more frequent, and more tests are run. When pregnant with twins, mothers may undergo several ultrasounds, and during the third trimester they go through non-stress test and biophysical profile. These tests may be done every 3-7 days before childbirth. When expecting twins, mothers should try to rest as much as possible and limit stress and strenuous activities. Lying on the left side is recommended for optimal blood flow.

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