What Are Fraternal Twins?

What Are Fraternal Twins?

Fraternal twins definition

Fraternal twins are commonly known as "non-identical twins" and can be simply defined as siblings who share the same womb but with different amniotic sacs and placentas. Biologically, they are said to be "dizygotic" meaning two different sperm cells fertilized two different eggs, which is how they are formed. They share up to half of their genetic structure as well.

The other set of twins is called "identical twins". They are biologically opposite to fraternal twins and are called "monozygotic", which means that an ovum was fertilized by a sperm, and later split into two. Identical twins are rare with cases of about 3 in every 1,000 deliveries, while fraternal twins are more common with as much as 20 and not less than 6 in 1,000 deliveries.

Having fraternal twins can be acquired as a genetic trait that runs in the family. If your mother or relatives have had fraternal twins, then you stand higher chances of having them as well. The trait is characterized by the inclination to hyperovulate in a menstrual cycle. In case you are a fraternal twin, your odds of having fraternal twins are higher.

Types of twins

  • Conjoined twins - after fertilization, it takes 12 days or more for the division to take place. They are rare and are joined in utero. Their occurrence is said to be based on a theory of fission, which is the partial or incomplete splitting of a fertilized egg.
  • Dichorionic diamniotic (DCDA) twins - most fraternal twins lie here. The twins are divided in four days and each has its own placenta and amniotic sac.
  • Monochorionic monoamniotic (MCMA) twins - both share one amniotic sac and the embryo takes nine days to split.
  • Monochorionic diamniotic (MCDA) twins - each has its own amniotic sac, but they share a placenta. The identical twins lie here and the embryo takes about four to a maximum of eight days to split.

How do fraternal twins fit?

They each have little tiny spaces since each has its own amniotic sac and placenta. The twins can be of the same or of different gender with the two having an equal chance of survival.

How do fraternal twins happen?

Having fraternal twins is rare since it is quite hard to find a pregnant mother releasing another ovum during the same menstrual cycle. This occurrence is called as "superfetation". However, this can only happen a couple of weeks after the conception of the first baby, which gives the explanation as to why one twin is considered mature and larger than the other.

A woman can conceive fraternal twins from different biological fathers, too. This is made possible by the fact that she is already pregnant with one, while she ovulates again. If she had sexual intercourse with another partner and conceives, the twins will be from different fathers.

Moreover, triplets can consist of fraternal or identical twins and a singleton. Pathologic assessment and careful examination of the membranes and placenta is important. The reason is that twins may appear similar in case they are fraternal and if they are identical, it will be quite easy to observe. The assessment and examination will be resourceful in knowing the type of twins a mother is carrying as well as determining whether they are identical or fraternal through testing each baby’s DNA.

Of twins born, a third are identical, making fraternal twins more common. As per every 100 births, two are fraternal. The rate of fraternal twins has been on the rise since the positive reception of fertility treatments.

What increases the odds of having fraternal twins?

  • If a mother has had fraternal twins before, she stands a higher chance of having them once more.
  • Engaging in a lot of sex during the fertile window can increase your chances of conceiving.
  • Adopting a reproductive technology that increases your ova release.
  • In case the mother is one from a set of fraternal twins.
  • Having a lot of children. Couples who set a limit on how many children they should raise have a decreased chance of getting twins.
  • Age of the mother. The younger she is, the lesser the chances of conceiving twins. Ladies aged 20 have lesser chances than those who are in their 30s, who also have lesser chances compared to those aged 35 and above, who have twice the luck of getting fraternal twins.
  • Races. African women have the highest chances of conceiving fraternal twins, with Asians having the least chances among all races.
  • Diet. Women who stand a higher chance of getting twins are those with a tendency of consuming sweet potatoes and yams.
  • Studies conducted have shown that taller women have a higher chance of getting fraternal twins as opposed to shorter ladies.
  • There has been some debate as to whether a woman's chance of getting twins is related to her father’s genetic structure. It is said to flow to their daughters, although a consensus has not been reached.

What do fraternal twins look like?

It is challenging to identify them at birth unless there are two placentas, which can be the same for identical twins. Each fraternal twin gets different characteristics as they mature and they cannot be termed to be similar in appearance or as identical twins, but rather appear like siblings.

There are fraternal twins who also appear different immediately after birth and can be identified separately according to their size, facial characteristics, and weight. However, they may be alike to the extent that their parents cannot tell them apart.

How will I know if I am pregnant with fraternal twins?

Fascinatingly, mothers of twins always say they knew they were carrying twins way before they tested scientifically. Pregnancy symptoms will be severe if you have twins, although the best way to be sure is to have an ultrasound. However, it may still be difficult to identify whether they are fraternal or identical at the early stages. The type of twins you are carrying can be well-identified at 12 weeks gestation.

Gestation for twins

The gestation period for a single baby is 40 weeks. For twins, their gestation is 38 weeks. It is two weeks shorter since the mothers' body will have and will be experiencing too many demands. In addition, the babies will not have enough of the nutrients they require. Most twins are prematurely born and usually have low birth weights. Their prematurity can be linked to disorders like jaundice.

The difference between fraternal and identical twins

Fraternal twins are dizygotic with separate placentas, supporting structures, and amniotic sacs. On the other hand, identical twins come from the same fertilized egg, can share supporting structures, placenta, and amniotic sac, but may not share them at all. Whether they share the sac or not, depends on the stage of cell division.

Fraternal twins do not have the same DNA. Thus, when the twins are a boy and girl, they are with no doubt, fraternal. A girl has XX chromosomes, and a boy has XY chromosomes. When the twins are a girl and a boy, it is made possible when one X egg is fertilized by an X sperm, and the other X egg is fertilized by a Y sperm.

It is possible also for twins of the same sex to be fraternal. Same sex twins can be identified as identical or fraternal through the help of an ultrasound. The most effective way is through DNA testing. Identical twins share the same DNA, although they may appear different due to factors such as their positions in the womb and the life they are exposed to after birth.

It is worth noting that twins are two different individuals, despite them being identical or fraternal.

Paternal twins

The traits or characteristics from the father are said to be paternal. Paternal twins are twins who inherited their father's characteristics. This, however, does not imply that their conception was as a result of their father's sperm cells. The conception of fraternal twins is completely dependent on the mother's ability to ovulate twice. Identical twins, on the other hand, have no relation to the sperm cell traits, although the reason is yet to be identified.

Twins with different fathers

Fathers of fraternal twins may be different. In such cases, the twins are said to be non-paternal twins. As unusual as this may sound, it has been proven through DNA tests.

Can genes influence someone to have fraternal or identical twins?

Genetics have been accredited for several years and has played a major role in twinning. In the 20th century, physicians found out that the daughters’ likelihood to get fraternal twins could be inherited from their father or mother. Getting fraternal twins is solely dependent on the mother. A recent research in genetics shows that several genes in animals, as well as humans, can influence one to get fraternal twins. Basically, the genes help in the growth of immature oocytes. These genes include bone morphogenic protein 15.

The different activity of proteins may result in women maturing multiple eggs in each menstrual cycle and increasing the chances of getting fraternal twins. It is fascinating how environment plays a role in twinning. Studies reveal that twins are conceived more during autumn and summer, and they try to find the connection, linking it to changes in food supply or daylight. The validity of this assumption is yet to be identified through research. More research shows that lifestyle habits such as smoking and the use of contraceptives affect the chances of getting fraternal twins.

What are the risks of having fraternal twins?

The risks are similar to those you are likely to experience when having identical twins. Moreover, expect the risk of transfusion from one twin to the other. The following are some of the risks involved in having fraternal twins:

  • Placenta previa
  • Delivery through C-section or Caesarean section. Twins must not necessarily be delivered through C-section since they can be vaginally delivered, unlike triplets. However, vaginal delivery of any twins is dependent on how the babies are positioned. If the baby nearer to the cervix is larger, or if the gestation period has exceeded 32 weeks, you can deliver your babies vaginally.
  • Placental abruption is linked to the risk of developing preeclampsia, and the risk increases once the first baby has been delivered.
  • Pregnancy-induced hypertension (PIH)
  • Delayed postnatal recovery period
  • Uterine growth restriction will result in low birth weight and premature delivery
  • Gestational diabetes happens due to the presence of two placentas, which will enable the body to resist insulin. Moreover, with time, the size of the placenta also increases. Thus, there will be a rise in placental hormones.

Other factors that increase the chances of having twins

Getting fraternal twins is mostly dependent on chance. Although other factors may determine or increase the chances of having the twins such as:

  • Age - The older you are, the higher your chances to conceive twins. It is argued through a scientific approach that for older women, the production of the follicle-stimulating hormone (FSH), is more than that produced by younger women. FSH is the hormone responsible for egg maturity prior to ovulation in each month. Although older women are less likely to conceive or take longer to conceive, statistics show that their chances of getting twins once they conceive are higher.
  • History of twins - If you have had fraternal twins in the past, your chance of having another set is higher.
  • Heredity - If your family has twins, or you yourself is a twin, then the likelihood of you getting twins is increased.
  • Number of pregnancies - The chance of getting twins also increases if there is an increased number of pregnancies.
  • Race - Although not quite explained, African and White women have a higher chance of getting twins as opposed to Asian and Hispanic women.
  • Body Type - Tall women with large bodies are more inclined to having fraternal twins than shorter women with smaller bodies.

Symptoms of multiple pregnancies

Oftentimes, women rely on their instincts to tell whether they are carrying more than one baby. However, there are better ways to be sure about it. The best and surest way to know whether you have one or more babies is through an ultrasound. The signs and symptoms of a multiple pregnancy include the following:

1) Raised hCG levels

Human chorionic gonadotropin or hCG is a hormone produced during pregnancy. When having more than one baby, its levels will be elevated. However, the levels of hCG are not a complete or an accurate indication of multiple pregnancies since it may be caused by other factors. It is important to find out the cause of high hCG levels if they are unusually higher than normal.

2) Doppler heartbeat count

A Doppler can detect a fetal heartbeat later in the first trimester. It can be conducted by qualified nurses and doctors, who can identify multiple heartbeats. It is not an accurate method since the same heartbeat can be detected in various sections of the abdomen.

3) Fetal movement

Women who have had babies before have experienced fetal movements way earlier than expected.

4) Excessive morning sickness

Morning sickness is a common symptom of most pregnant women during the first trimester. In fact, about half of all pregnant women suffer from morning sickness. Mothers to multiple babies experience severe morning sickness, while others do not. Therefore, just because you are experiencing excessive morning sickness does not necessarily mean you are having more than one baby in your tummy.

5) Weight gain

It is normal to gain weight due to eating habits while pregnant. Not all women who gain weight are even pregnant. It is common to gain weight during pregnancy, even if you are carrying a singleton. However, if you happen to gain ten more pounds than usual during pregnancy, you may be having a multiple pregnancy.

6) Abnormal AFP results

Alpha-fetoprotein (AFP) test is done in the second trimester. It is commonly referred to as the "triple marker test". It measures the amount of protein the fetus' liver secretes. If the amount secreted is higher or comes out positive, then chances are you are carrying multiples. The test can also be used to identify some types of birth defects.

7) Large gestational age

Most midwives and doctors monitor the fundal height, which is the distance from the pubic bone to the topmost part of the uterus. Women carrying multiples tend to have a larger gestational age, as a result of uterine stretching. It is not accurate since a large gestational age may be as a result of other factors as well.

Giving birth to twins

It is not unusual for singleton birth complications to arise. Thus, extra precaution should be taken in the case of twins. Women are encouraged to give birth at the hospital. Caesarean section is often preferred, although one can give birth normally, through the vagina. If you prefer giving birth vaginally, you should consider a pain relief strategy such as getting an epidural.

If one baby is in a transverse position, or if the baby closest to the uterus is in a breech position, then a Caesarean section is inevitable. It is also recommended in case you have had previous complications in delivering a single baby.

Points to remember if you are expecting twins

  • Get adequate rest. It requires a lot of energy to support twins.
  • Have regular ultrasounds. As opposed to carrying a single baby, you are advised to have more ultrasounds when you are carrying twins.
  • Organize yourself earlier. As previously mentioned, the gestation period of twins is shorter. Hence, it is important to have earlier preparations.
  • Have a regular antenatal care.
  • Seek advice from a dietitian since you and the babies will require nutrients all throughout your pregnancy.