Facts About Multiples
An Encyclopedia of Multiple Birth Records

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There are many risks associated with multiple pregnancies and births, this is a small overview of some of the more common issues, such as death in utero (not taking into account why they occurred), prematurity, Twin to Twin Transfusion Syndrome, and other issues. I am not a health professional or scientist, this is basic info and stats I have culled from many sources. Please do not email me questions asking about specific illnesses, as I am not qualified to answer them.

Monochorionic/amniotic twins have a 50% chance of dying due to cord entanglement.

In 1977 fetal deaths per 1000 births were 9.3% for singletons, 35.1% for twins and 67.7% for higher order.
In 1985 the stats dropped slightly to 7.9% for singletons, 27.9% for twins and 76.3% for higher order (which can probably be attributed to more higher order births in general).
In 1987 the rates were 7.3% for singletons, 25.9% for twins and 43.5% for higher order.

From my own statistics of quintuplets, 28.55% of sets will have at least one fetal death. I believe this statistic is a bit low, as some sets were never updated on or information on survivors wasn't available.

MOST Online reports that 98.8% of triplets survive pregnancy and the first year, while the rate is 96.8% for quads, 90.5% for quintuplets and 100% for sextuplets (of their surveyed members. [See site]

Birth prior to 37 weeks is considered premature for singletons. For twins, many consider 37 weeks to be term, as longer gestations can sometimes be dangerous for multiples because space in the womb is less than that for a single birth and the placenta begins to break down sooner. Here are some stats on survival rates for premature births.

Chance of survival:

21 weeks and less - under 1%
22 weeks - under 2%
23 weeks - 5 - 25%
24 weeks - 40 - 60%
25 weeks - 50 - 80%
26 weeks - 80 - 90%
27 weeks - up to 90%
30 weeks - up to 95%
34 weeks - up to 98%

Some singleton babies who were born very early in the US and survived:

Marcus Richardson - 19 weeks, 6 days (January 1972)
Melissa Cameron - 20 weeks (December 1983)
Kanya King - 21 weeks (June 16 1985) 1lb 2ozs
Kelly Thorman - 21 weeks (March 1971) 
Suzanne South - 21 weeks (July 1971) 

In the UK the most premature single baby was born at 21 weeks, 6 days.

The lightest baby that has survived weighed 8.6ozs (and she is a twin - her twin was 1lb 4ozs).

It is estimated that over 100 children have been born in the US weighing less than one pound and have survived.

These rates have risen dramatically, as in 1988, babies at 24/25 weeks only survived about 25% of the time, 26 weeks only 50% survived, and 27/28 weeks only 75%.

Many infants born before 37 weeks run the risk of suffering from brain bleeds, heart problems, insufficient lungs, hernias and other medical problems. Later in life they may present with various disabilities, ranging from cerebral palsy, eye problems, deafness, mental disabilities, attention problems, and poor coordination. Many doctors consider 28 weeks as a goal for multiple pregnancies, since most babies have better developed lungs by this time.

Dichorionic twins have a 1 in 20 chance of delivery before 32 weeks.

Preterm birth rate for twins: 40.9% (1981), 55% (1997)

In 1987, 82% of twins were less than 6lbs 10ozs, 50% were less than 5lbs 8ozs (Low Birth Weight), and 10% were less than 3lbs 4ozs (Very Low Birth Weight).

The average weights are:

Singleton - 7lbs 7ozs
Twins - 5lbs 5ozs
Triplets - 4lbs 2ozs each
Quadruplets - 3lbs 6ozs each
Quintuplets - 2lbs 13ozs each
Sextuplets - 2lbs 8ozs

[Stats from MOST Online's survey]

A more than 25% weight difference between each twin occurs between 4-9% of the time.

20-30% of Very Low Birth Weight babies have an incidence of handicaps that present in the first 2-3 years. An additional 40-50% will be diagnosed with learning, coordination disabilities, ADD or other problems before age 11.

RDS

If the babies lungs are too immature at birth to provide lubrication, the lungs will collapse every time the baby exhales. This affects 10 to 20% of all preemies and 50% of all Very Low Birth Weight (below 3lbs 4ozs) babies.

After 28 weeks, boys are more vulnerable than girls (boys develop slower). Second born twins are more at risk than first born (because they are more likely to have a stressful delivery).

About 80% of babies with RDS will survive. It is treated by giving supplemental oxygen, respirator treatment, and steroids given before birth.

Retinopathy

Babies being treated with excessive amounts of oxygen may have the vessels of their retinas affected. It is the leading cause of blindness in preemies. The retina may grow too many blood vessels, cause excessive fluid to build up, or scarring, or it may detach altogether.

It causes about 2600 cases of vision loss a year with total blindness in about 650 Very Low Birth Weight babies. 1 in 6 VLBW babies born before 30 weeks will develop some form of ROP.

Twin to Twin Transfusion Syndrome is a disease of the placenta, due to the sharing of blood vessels and connections through the placenta. The larger baby (recipient) may suffer from heart problems due to the increased blood flow and thicker blood it receives, while the smaller baby (donor) can suffer from severe anemia from lack of blood. The babies themselves are normal, it is the placenta that causes the problems. The rate of survival for TTTS when nothing is done to help the twins is 10%. The rate of survival is much higher when the condition is diagnosed, monitored and treated. TTTS can also occur in higher order multiple births.

TTTS occurs based on how the twins are formed:

Monochorionic/Monoamniotic (sharing both the inner and outer sac) (Mo/Mo)

Sharing both sacs occurs in 1-5% of identical twin pregnancies.

TTTS can occur, but it is much harder to detect because they share an amniotic sac, and amniotic fluid, and that is how they test for TTTS. Recent research is showing that TTTS may affect Mo/Mo twins at a similar rate to Mo/Di twins (previously it was thought rare in Mo/Mo twins).

Monochorionic/Diamniotic (share outer sac, separate inner sacs) (Mo/Di)

Monochorionic/Diamniotic (Mo/Di) occurs in 65-70% of identical twin pregnancies.

In 10-15% of these pregnancies TTTS will occur.

Dichorionic/Diamniotic (twins in separate outer and inner sacs) (Di/Di)

Occurs 25-30% of identical twin pregnancies. All fraternal twins will be Di/Di.

TTTS does not usually occur, but may occur in those twins with fused placentas. 30% of fused placentas are identical twins, and 1% of them shared blood vessel connections to the placenta.

It has been known to occur in twins with different blood types (a rare condition called chimerism).

Things That Occur During TTTS:

Polyhydramnios - Excessive amniotic fluid. Happens to the recipient twin. Can also occur in non TTTS cases.
Oligohydramnios - Depleted amniotic fluid. Happens to the donor twin.

Acardiac twin occurs in 1 in 35,000 pregnancies. It results from reverse blood flow through the body of one twin as it is pumped by the other (the pump twin), called Twin Reverse Arterial Perfusion Syndrome (TRAP). The pump twin is typically normal, but at risk for developing heart failure because it pumps blood for itself and its twin. The acardiac twin presents with anomalies such as absent or unformed heart (acardiac means no heart), no head or brain (acephalus), severe swelling and other problems. The acardiac twin cannot survive.

Without treatment 50-75% of these pregnancies are lost. Treatment comes in the form of surgery to interrupt the blood flow to the acardiac twin without harming the pump twin, so the pump twin will no longer have to pump to the acardiac twin. Umbilical cord ligation can be used, where a knot is tied in the umbilical cord of the acardiac twin. Radio frequency ablation can also be used to halt the flow of blood between the twins.

Since the use of ultrasound has become routine, doctors have noticed a phenomenon that has been dubbed 'Vanishing Twin Syndrome'. A woman may conceive twins and they may be visible on an early ultrasound. But sometimes at a follow up ultrasound within the first trimester, one of the sacs will have disappeared. The mother may not have even been aware that one of the twins was lost. Sometimes the sac and fetus is reabsorbed into the mother, or the surviving twin. Sometimes it is lost as a miscarriage, but only one twin is lost. This is why a lot of doctors will caution women diagnosed with twins that the twins may not make it past the first trimester. Vanishing twin syndrome seems to stop after the first trimester.

Researchers have speculated that 50 - 80% of twin conceptions end in the birth of a single child due to one fetus vanishing. Another statistic I heard was that 1 in 8 pregnancies begin as twins, but I've also heard 1 in 12. Some women may not have even been aware they ever conceived twins, as some are lost within days of conception. A researcher theorized that half the people on earth may be walking around thinking they're a singleton, when they were actually conceived a twin.

In one study, 325 twin pregnancies were identified very early by ultrasound and followed through the entire pregnancy. They reported that 61 (18.8%) ended as twin births, 125 (38.5%) ended as singleton births, and 139 (42.8%) ended as a complete loss. So if you have one hundred women conceive twins (whether they know it or not), only 18-19 will actually have twins.

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