In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.
Identical, or monozygotic, twins may or may not share the same amniotic sac, depending on how early the single fertilized egg divides into 2. If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA.
Mixed-gender twins are the most common type of fraternals, some 50 percent are boy-girl. To understand this combination: Males have XY chromosomes, females have XX chromosomes.
Monoamniotic-monochorionic Twins
This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords. If you have monoamniotic-monochorionic twins, your healthcare provider will monitor your pregnancy closely.
The first wife (died ante 1770), of Feodor Vassilyev (b. 1707–c. 1782), a peasant from Shuya, Russia, gave birth to 16 sets of twins.
Twins are at increased risk of fetal and infant death compared with singleton births. 1-3 The increased risk is partly the result of the lower birthweight and gestational age at delivery of multiple pregnancies. At particular risk are monozygotic twins who have poorer survival rates than dizygotic twins.
Factors that increase the chance of twins include: consuming high amounts of dairy foods, being over the age of 30, and conceiving while breastfeeding. Many fertility drugs including Clomid, Gonal-F, and Follistim also increase the odds of a twin pregnancy.
“Some of the cells contain the chromosomes from the first sperm while the remaining cells contain chromosomes from the second sperm, resulting in the twins sharing only a proportion rather than 100% of the same paternal DNA,” clinical geneticist Dr. Michael Gabbett, who worked with Fisk, says.
However, males are slightly more likely than females to die in the womb. And because the death rate in the womb is higher for twins than for singleton births, female twins are more common than male twins.
The quick answer to this question is that, in a twin pregnancy, it is the mother's genes that determine twins. First up, giving birth to identical twins is not genetic, but conceiving fraternal twins is. The mother may have the genetic trait of releasing two eggs in one menstrual cycle.
#1 Fraternal twins can be conceived as much as 24 days apart
For this reason, fraternal twins can be conceived a few weeks apart, though they generally will be born at the same time.
Yes! Identical twins came from the same sperm and egg, so they have the same chromosomes and genes. But there are environmental differences that can affect the way they look and behave.
As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood.
Since conception happened for each egg, each egg carries the sex chromosome of the father. A girl has XX chromosomes while a boy has XY chromosomes. A boy-girl combination is the most common form of these kind of twins.
A couple of findings on ultrasound can help. If a first trimester ultrasound between weeks 8 and 13 shows that the fetuses share one placenta(or are “monochorionic”), the fetuses are identical more than 99% of the time. However, if the fetuses have two separate placentas, they can still be identical.
Despite the name, identical twins are rarely completely identical. Their skin tone, weight, height, or personality, to name a few characteristics, may be different. How does this happen? Every time a cell divides—as occurs in the developing embryo—your DNA must replicate, a very complicated process.
Superfetation is a rare event that involves getting pregnant a second time while you're already pregnant. It's so uncommon that cases of superfetation often make headlines. Your body does a good job preventing subsequent pregnancies once an embryo is developing inside your uterus.
No.
That's not all, Monga says. Women pregnant with twins complain of more back pain, sleeping difficulties, and heartburn than those who are carrying one child. Being pregnant with twins also carries a higher rate of maternal anemia and a higher rate of postpartum hemorrhage (bleeding) after delivery.
Twin births aren't exactly common. In humans, they occur in one to three per cent of all births. Previous studies of the phenomenon have concluded that mothers of twins are more fertile than other women. This is because on average they give birth more often than other mothers.
The National Organization of Mothers of Twins Clubs claims that once you have had fraternal (dizygotic) twins, your chances of having another set are three to four times greater than that of the general population. Both hereditary and environmental factors may contribute to this.
While there are risks associated with all twin pregnancies, dizygotic (fraternal) twin pregnancies usually bring about the least amount of complications, carrying the lowest risk of all types of twins.
A pregnancy with fraternal twins has the lowest risk of all multiple pregnancies. This is because each baby has its own placenta and amniotic sac. You will sometimes hear fraternal twins referred to as 'dizygotic' twins.
The causes of fetal death vary and include twin–twin transfusion, placental insufficiency, intrauterine growth retardation related to preeclampsia, velamentous insertion of the cord, cord stricture, cord around the neck, and congenital abnormalities [5].
Most often, fetuses known in utero as twin A are also first born and thus retain their label. However, this is not always the case, such that the twin A newborn was previously labeled twin B in utero and vice versa.