In the majority of vaginal births, Baby A is born first. But occasionally the twins switch positions at the last minute, and Baby B emerges first, as further noted by the Stanford Medicine News Center. Still, the birth order is relatively straightforward.
Twins are defined as two offspring born together, but that doesn't necessarily mean they are born on the same date. Multiples are generally born only a few minutes apart. If delivered by cesarian section, the interval between births is usually only a minute, maybe two.
In addition, previous studies have shown that first-born twins are, on average, taller and heavier than second-born twins until adolescence (Silventoinen et al., 2007; Pietiläinen et al., 2002).
The gene versions that increase the chance of hyperovulation can be passed down from parent to child. This is why fraternal twins run in families. However, only women ovulate. So, the mother's genes control this and the fathers don't.
However, many birth order experts agree that twins tend to organize themselves according to their overall place within the family. 2 For example, if they have one older sibling, they will both exhibit characteristics of a second born. If they are the oldest, they will adopt some traits of firstborns.
In the majority of vaginal births, Baby A is born first. But occasionally the twins switch positions at the last minute, and Baby B emerges first, as further noted by the Stanford Medicine News Center. Still, the birth order is relatively straightforward.
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.
Older women generally have a higher chance of conceiving twins. A 35 year old woman is about 4 times more likely to have fraternal twins than a 15 year old! That is because they are experiencing some hormonal changes as they near menopause. This could encourage their body to release more than one egg during ovulation.
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.
Many people believe twins skip a generation, but that's just a myth. The idea that twins skip generations likely comes from the fact that the genetic factors contributing to twins only come from the gestational parent's side.
Identical twinning and family heredity
Since embryo splitting is a random spontaneous event that happens by chance, it doesn't run in families. Genes are not involved and there's no scientific evidence that being from a family with identical multiples has any impact on your odds of having twins.
A parasitic twin is an identical twin that has stopped developing during gestation, but is physically attached to the fully developing twin. The fully developed twin is also known as the dominant or autosite twin.
While 40 weeks is the full gestation period of the average pregnancy, most twin pregnancies are delivered at approximately 36 weeks (range 32-38 weeks depending on the type of twin pregnancy).
Which twin is older? The oldest twin is the one who is born first. It doesn't matter whether twins are born vaginally or by C-section; the first one out of the womb is considered the oldest. This may be the baby who was labeled baby A during the ultrasounds, but it might not if the other one makes it out first.
According to The American Society for Reproductive Medicine, women who are fraternal twins have a 1 in 60 chance of having twins, and men who are fraternal twins have a 1 in 125 chance of fathering twins. It was previously believed that identical (monozygotic) twins were random — not genetic.
It's estimated that 1 in 250 pregnancies results in twins naturally, and there are two ways to conceive them.
The embryonic and fetal development of twins in the womb parallels that of singletons – they develop on the very same schedule. Around 26 weeks of gestation twins do slow down a bit in growth in comparison to singletons, as their environment gets pretty crowded!
You're more likely to have a vaginal birth if the first twin is in a head-down position. But there may be medical reasons why a vaginal birth is not recommended. If you have had a caesarean section before, for example, it's not usually recommended that you have a vaginal birth with twins.
Several factors for causes of embryo splitting were suggested, including maternal age, prolonged embryo culture, ovarian stimulation, and zona pellucida (ZP) manipulation [6].
The Science of Fraternal Twins. Mixed-gender twins are the most common type of fraternals, some 50 percent are boy-girl.
Monoamniotic-monochorionic Twins
These types of twins share a chorion, placenta, and an amniotic sac. This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords.
Age. According to the Office on Women's Health , women who are aged 30 years or older are more likely to conceive twins. The reason for this is that women of this age are more likely than younger women to release more than one egg during their reproductive cycle.
Is there a third type? Traditionally, the science around twins has taught that identical and fraternal are the only two types. But a third type might exist, called polar body or half-identical twins.
Fortunately telling twins apart is one fear that can be taken off the list. Most parents find that mixing up their babies is the least of their concerns. After only a few hours or days at most, they are distinguishable as individuals. Even if they look alike, parents just know the difference.
Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families. But there are some factors that make having non-identical twins more likely: non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese.