Fraternal twins

22.03.2023

2 min. Reading time

In the common imagination, identical twins and fraternal twins are often associated with multiple pregnancies. In medical terminology, these terms are rarely used. Nevertheless, it is useful to know what fraternal twins are and what such a pregnancy looks like.

Fraternal twins – how do they come about?

Fraternal (dizygotic) twins, as the name suggests, are formed from two different ovules fertilised by two different sperm. This is most often the case when two ovules are released during ovulation. In very rare cases, the sperm come from two men. The resulting foetuses later develop independently of each other in the two amniotic sacs. Virtually all fraternal twins also have their own placenta – these are twin pregnancies (with a few exceptions). Multiple pregnancies, including twins, are always considered high-risk and require more frequent visits to the gynaecologist.

Fraternal twins – Gender

Fraternal twins, unlike identical twins, can have different sexes. This is because the two ovules are fertilised by different sperm and the further cell divisions take place independently of each other. So fraternal twins can be two girls, two boys or one boy and one girl. The chance for each of these constellations is the same. In contrast to identical twins, these children also differ in appearance. They resemble each other like siblings, but they are not identical.

Fraternal twins – complications during pregnancy

Twin pregnancies are associated with a higher risk of complications. The most common of these are:

Premature birth
Limiting growth
Polio
High blood pressure
Untreatable vomiting in a pregnant woman

In fraternal pregnancies, it is recommended to have an ultrasound scan every 4 weeks from the 20th week of pregnancy. This allows better monitoring of the foetal growth.

Fraternal twins – Birth

In multiple pregnancies, delivery often occurs earlier than 40 weeks of gestation. In twin pregnancies, this is usually 37-39 weeks of gestation. A longer duration of pregnancy can lead to serious complications such as the death of one or both foetuses. Natural birth is possible in fraternal pregnancies if the first twin is in the head-down position. It is also important that the weight of the babies is not too far apart (<20%). The decision about the time and way of delivery depends on the obstetric situation and the presence of possible complications, as well as the well-being of the babies.