In prenatal ultrasounds, the baby positioned lowest in the uterus is given the designation of “Baby A.” Under this convention, Baby A will likely be born first in a vaginal delivery. However, about 75 percent of twins are delivered by cesarean section.
OBJECTIVE: By convention, twins are labeled as twin A or twin B at the time of birth, depending on their birth order. However, antenatally twins are labeled as A or B according to their location relative to the birth canal. Antenatal labeling is usually established by prenatal ultrasound.
One twin will be called baby A and the other twin will be called baby B. The reason they are labeled this way is that, during vaginal birth, the baby in the sac that includes the cervix will be born first. This baby is called baby A. The baby born afterward is logically labeled baby B.
Often, baby A (so named because she's closest to the cervix and therefore likely to be born first) will stay on one side while baby B stays on the other. The less room they have, the less likely they are to move around.
For vaginal delivery of both infants, the twins decide birth order by their placement in the uterus. Once the babies are large enough to stay in one position in the womb, the twin lowest in the uterus is known as Baby A and the one furthest from there is Baby B, according to the Stanford Medicine News Center.
As a parent of twins, I'm pretty sure that you know the answer to the question “which twin is older?” It is, of course, the child that was born first.
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.
To make sure twins and higher-order multiples get the right treatments, the newborns must be matched to their prenatal identifiers — Baby A, Baby B, and so on — at birth. That often means breaking with the obstetric tradition of calling the first-born “Baby A.”
Identical (monozygotic) twins happen when a single egg (zygote) is fertilised. The egg then divides in 2, creating identical twins who share the same genes. Identical twins are always the same sex, so if your twins are identical, you'll have 2 girls or 2 boys.
Twin B has been noted to be heavier than A in 41 to 55% twin gestations. When the first twin was larger, the weight differences were greater than when the second twin was the larger one. A difference of more than 250 g occurred in 43.4% (A>B in 23.1% and B>A in 20.3%).
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.
Classically, the bigger twin is the more physically dominant. It's basic human nature, and particularly applicable to boys as they hit puberty. It happens often with singleton siblings too… the older is bigger and enforces him/herself through physical dominance.
Dizygotic (DZ) twins, also called fraternal twins, occur when two egg cells are each fertilized by a different sperm cell in the same menstrual cycle. DZ twins are about twice as common as MZ twins, and they are much more likely to run in families.
Barring pregnancies that result from assisted reproductive technology, dizygotic twins are far more common than monozygotic twins and account for 70 percent of all twin gestations.
As per the university, MoMo twins are some of the rarest types of twins, making up less than one per cent of all births in the United States. According to Dr Gupta, MoMo twins account for “fewer than 0.1 per cent of all pregnancies and one per cent of identical twins”.
Monochorionic-monoamniotic twins are identical twins that share both a placenta and an amniotic sac. This is the rarest and highest risk form of twin pregnancies.
Monochorionic Monoamniotic Twins
These types of twins share the same chorion, placenta and amnion. This is the rarest type of twin pregnancy – only affecting 1 in every 100 sets of identical twins – and it comes with a higher risk of complications because the foetuses can get tangled in their umbilical cords.
Superfecundation is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse, which can lead to twin babies from two separate biological fathers.
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.
Semi-identical twins are rare, and doctors say they've identified the second case ever | CNN. You've probably heard of identical and fraternal twins, but a report released this week says there's a third kind -- sesquizygous twins or "semi-identical." Researchers say they share anywhere from 50 to 100% of their genomes.
The results suggest that twin fetuses are aware of their counterparts in the womb, that they prefer to interact with them, and that they respond to them in special ways. Contact between them appeared to be planned—not an accidental outcome of spatial proximity, says study co-author Cristina Becchio of Turin.