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).
Most twin, triplet or more babies will be slightly different in size, but sometimes 1 baby is significantly smaller than the other/s. This is called 'selective' fetal growth restriction.
Yes there is genetic variation and some younger siblings may be taller than the first, but the majority are not as tall as the first born. There can be many reasons for this, but most likely it is the health and nutritional status of the mother declines and depletes with every pregnancy.
Depending on where they implant, one twin may get a smaller share of the placenta than the other, resulting in less blood flow and nutrition to one fetus, and more to the other. This is called unequal placental sharing. As a result, the twins may grow differently.
Fraternal twins — the most common kind of twins — occur when two separate eggs are fertilized by two different sperm. Each twin has his or her own placenta and amniotic sac. The twins can be two girls, two boys, or a boy and a girl.
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.
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.
Most twins, triplets and more grow and develop along roughly the same lines as their singleton peers – even those who start out much smaller will catch up in time.
Dichorionic twins have entirely separate fetal-placenta blood circulations, and thus the larger twin is unaffected. For the smaller twin, however, the condition can be life threatening. With monochorionic twins, the risks are increased because the twins share blood vessels in the placenta.
There is no right or wrong answer, it's a personal preference. Some chose to be completely open or tell their twins to give a “smaller” twin leverage if he/she is older. Other choose not to tell so that they don't bicker about the subject or the dominate “older” twin doesn't have more leverage.
“Having twins is not twice as hard—it's exponentially more difficult,” says Natalie Diaz, author of What To Do When You're Having Two and CEO of Twiniversity, a global support network for parents of twins.
Typical Twin Conception
Although two fetuses develop simultaneously in superfetation, they differ in maturity, having been conceived days or even weeks apart. Superfetation is observed in animal reproduction, but it is exceedingly rare in humans.
It is estimated that 1 in 250 natural pregnancies will naturally result in twins. While twin pregnancies can happen by chance, there are some factors that may increase your odds of having two babies at the same time.
Some identical twins can have different heights and weights. This is because height and weight are controlled by what you eat as well your DNA. Differences in diet can start earlier than you might imagine. When the twins are growing inside the uterus, there can be differences in how well they connect to the placenta.
Consequently, a considerable proportion of twins experience a very early loss of their co-twin. Previous studies indicate that loss of a co-twin by death in childhood or adulthood is associated with considerable mental morbidities among the surviving twins (Segal and Bouchard, 1993; Woodward, 1988).
Conclusions: During the first 2.5 years of life, there is a difference in growth between twins and singletons. Twins catch up in their body size, i.e. they grow faster after birth, but do not yet achieve the same height and weight till they reach 2.5 years of age.
This is why fraternal twins run in families. However, only women ovulate. So, the mother's genes control this and the fathers don't. This is why having a background of twins in the family matters only if it is on the mother's side.
Heredity on the mother's side ups a couple's odds of conceiving fraternal twins.
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.
Triplets and identical twins who share a placenta and amniotic sac (Monochorionic monoamniotic or MCMA) are the most likely to experience problems. This is followed by identical twins who share a placenta, but have their own amniotic sacs (Monochorionic diamniotic or MCDA) .
Most practitioners advise women who start their twin pregnancy at a normal weight to gain 37 to 54 pounds. You should gain a little more if you were underweight (between 50 and 62 pounds) and a little less if you were overweight (between 31 and 50 pounds).
While the average single baby weighs 7 pounds at birth, the average twin weighs 5.5 pounds. Triplets typically weigh 4 pounds each, and quads weigh 3 pounds each. Babies born at under 5.5 pounds are considered to have a low birth weight.