Multiple Birth Gestation and Birth Weight Data

Newborn twins side by side under blanket

Juanmonino / Getty Images

A report issued by the National Vital Statistics Report in 2018 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.

The Average Birthweight of 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 2017, 19.51% of twins were born early preterm, (which is defined as prior to 34 weeks) and more than half (59.43%) were born prior to 37 weeks gestation. By comparison, only 9.93% of singletons are born before 37 weeks and 2.76% were born before 34 weeks.

Low birth weight is defined as less than 2,500 grams or 5 pounds, 8 ounces. Very low birth weight is defined as weighing less than 1,500 grams or 3 pounds, 5 ounces. Over half of twins (55.39%) met the definition of low birth weight and 9.45% of twins born in 2017 were classified as very low birth weight.

The Average Birthweight of Triplets

A total of 3,675 babies were part of a triplet birth in 2017. More than ninety percent (98.83%) were born preterm (before 37 weeks) and 67.51% were considered early preterm (born before 34 weeks).

Triplets are generally less than half the size of a singleton baby. More than a third of triplets born in 2017 were very low birth weight.

The Average Birthweight of Quadruplets

Quadruplets, babies born in sets of four, have increased risk. 193 babies were born as quadruplets in 2017. All were born preterm and 91.71% were born early preterm (less than 34 weeks).

Similarly, all quadruplets weighed less than five pounds, eight ounces, and 67.91% weighed less than three pounds, five ounces.

The Average Birthweight of Quintuplets and Higher

Out of the 49 babies born as higher-order multiples like quintuplets, sextuplets, septuplets or octuplets, all were born early preterm (before 34 weeks).

All higher-order multiples were low birth weight and 93.88% were very low birth weight in 2017.

Gestational Age and Birth Characteristics

US Births 2009
All Births Singletons Twins Triplets Quadruplets Quintuplets+
Number 4,130,665 3,987,108 137,217 5,905 333 80
Percent very preterm (<32 wks) 2.0 1.6 11.4 36.8 64.5 95.0
Percent preterm (<37.5 wks) 12.2 10.4 58.8 94.4 98.3 96.3
Mean gestational age (weeks) 38.6 38.7 35.5 31.9 29.5 26.6
Percent Very Low Birth Weight (<1,500 g or 3 lbs. 5 oz.) 1.5 1.1 9.9 35.0 68.1 86.5

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

8.2 6.4 56.6 95.1 98.6 94.6
Mean birthweight in grams (and pounds) 3262
(7 lbs. 3 oz.)
(7 lbs. 4 oz.)
(5 lbs. 2 oz.)
(3 lbs. 10.5 oz.)
(2 lbs. 13.5 oz.)
(2 lbs. 3 oz.)
1 Source
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  1. Centers for Disease Control and Prevention. National Vital Statistics Reports.

By Pamela Prindle Fierro
 Pamela Prindle Fierro is the author of several parenting books and the mother of twin girls.