Multiple Birth Gestation and Birthweight Data

Are twins and multiples born smaller than singletons?

Tiny newborn twins
Are multiples born earlier and smaller?. Juanmonino / E+ /Getty Images

A report issued by the National Vital Statistics Report in late 2011 revealed some interesting data about twins, triplets and other multiples and how they stack up against singleton births. The numbers make it clear that multiples are born earlier and smaller, weighing less than their singleton counterparts.

Twins

While the risks for twins are not as elevated as they are for higher order multiples, twins are still more likely to be born early and weigh less.

In the data which was collected from births in the year 2009, 11.4 percent of twins were born very preterm, (which is defined as prior to 32 weeks) and more than half (58.8%) were born prior to 37 weeks gestation. By comparison, only 10 percent of singletons are born before 37 weeks and less than 2 percent are born before 32 weeks.

  • The mean gestational age for twins was 35.3 weeks.

Low birthweight is defined as less than 2,500 grams or 5 pounds, 8 ounces. Very low birthweight is defined as weighing less than 1,500 grams or 3 pounds, 5 ounces. Over half of twins (56.6%) met the definition of low birthweight and ten percent of twins born in 2009 were classified as very low birthweight.

  • The average weight for twins was five pounds, 2 ounces (2,336 grams).

Triplets

Nearly 6,000 babies were part of a triplet birth in 2009. More than ninety percent (94.4%) were born preterm (before 37 weeks) and thirty-seven percent (36.8) were considered very preterm (born before 32 weeks).

  • The mean gestational age for triplets born was 31.9 weeks.

Triplets are generally less than half the size of a singleton baby. More than a third of triplets born in 2009 were very low birthweight.

  • The average weight of triplet babies was three pounds, 10.5 ounces.

Quadruplets

Quadruplets, babies born in sets of four, have increased risk.

355 babies were born as quadruplets in 2009. Nearly all -- 98.3 percent -- were born preterm and more than half -- 64.5 percent -- were born very preterm (less than 32 weeks).

  • The mean gestational age for quadruplets born in 2009 was 29.5 weeks

Similarly, nearly all quadruplets -- 98.6 percent -- weighed less than five pounds, eight ounces, and more than two-thirds (68.1 percent) weighed less than three pounds, five ounces.

  • In 2009, the average quadruplet weighed two pounds, 13.5 ounces at birth.

Quintuplets and Higher

In 2009, several sets of extreme supertwins were born. They include quintuplets (5), sextuplets (6), septuplets (7) and even octuplets, a set of eight babies. 2009 saw the birth of the first surviving set of octuplets (eight babies), the Suleman octuplets born in California. These babies were born at 30.5 weeks gestation, surprisingly well beyond the average 26.6 week gestation for extreme supertwins. Out of the 80 babies born as higher order multiples like quintuplets, sextuplets, septuplets or octuplets, nearly all were born early.

96.3% were preterm (before 37 weeks) and 95.0 were very preterm. Other higher order multiples born in 2009 include the Stansel sextuplets (2 surviving), the Jones quintuplets (featured on the TLC television program, "Quints by Surprise"), The Maskell-Mistalski quintuplets (four surviving), and the Conklin quintuplets from Pennsylvania.

The average gestation for quintuplets and higher order multiples in 2009 was 26.6 weeks.

Due to their extended gestation, the Suleman octuplets weighed between 1 pound, 8 ounces and 3 pounds and 4 ounces. 86.5 % of quintuplets+ were very low birthweight and 94.5% were low birthweight in 2009.

The average birthweight for quintuplets and higher in 2009 was 2 pounds, 3 ounces.

Gestational Age and Birth Characteristics

US Births 2009
 All BirthsSingletonsTwinsTripletsQuadrupletsQuintuplets+
Number4,130,6653,987,108137,2175,90533380
Percent very preterm (<32 wks)2.01.611.436.864.595.0
Percent preterm (<37.5 wks)12.210.458.894.498.396.3
Mean gestational age (weeks)38.638.735.531.929.526.6
Percent Very Low Birth Weight  (<1,500 g or 3 lbs. 5 oz.)1.51.19.935.068.186.5

Percent low birthweight            (<2,500 g or 5 lbs. 8 oz.)

8.2  6.456.695.198.694.6
Mean birthweight in grams (and pounds)3262
(7 lbs. 3 oz.)
3296
(7 lbs. 4 oz.)
2336
(5 lbs. 2 oz.)
1660
(3 lbs. 10.5 oz.)
1291
(2 lbs. 13.5 oz.)
1002
(2 lbs. 3 oz.)

Source:

Martin, J., et al. "Births: Final Data for 2009." National Vital Statistics Reports, Volume 60, November 2011.

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