Research Study Finds Birth Weight of Multiples Lowering Over Last 40 Years

FRANKLIN, Tenn. - Dec. 1, 2025 - PRLog -- Multiple blessings sometimes arrive in smaller packages today than they did in 1985 or 2005, according to the results of recent research by Multiples of America. The study found that in a pair of twins, the lowest birthweight of a multiple has decreased over the past 40 years, with the smallest multiple birthweight recorded in 1985 at just "under two pounds;" in 2005 at 1 pound, 3 ounces, and in 2025 at 1 pound, 1/2 ounce.

The study on the "Birth Weight of Multiples" was completed by Multiples of America from March through July 2025. A survey, which mirrored studies under the same name conducted in 1985 and 2005, asked respondents to answer 14 questions. More than 740 parents of multiples responded to this survey, topping the response rate of all organizational studies over the last 20 years.

Along with birthweight, questions also collected information about birth order. In 1985, respondents reported no correlation between birth order and size. However, the 2005 had a different outcome, noting that Baby A had a slightly higher chance of being heavier at birth than Baby B. The 2025 findings substantiate 2005's outcome with 54.85% of respondents indicating that Baby A weighed more at birth.

Weight gain during pregnancy for those expecting twins, triplets or more was another notable change from the findings in previous years. In 2005, 19.2% of respondents gained up to 30 pounds, however in 2025, 34% reported gaining up to 30 pounds, with the largest percentage (20.6%) reporting a gain of 21-30 pounds. On the flip side, the percentage of moms gaining 31-60 pounds tallied higher in 2005 than now.

Additional questions on the survey led to findings in areas including the impact of birth order on birthweight, the prevalence of identical vs. fraternal twins, multiples' gestational age at birth, and medical complications during pregnancy. A full summary was published in the November issue of the organizational ezine, Multiple Connections.

This study now becomes part of the collection of organizational research conducted by Multiples of America over six decades. Other studies have focused on topics such as post-partum depression, marriage and multiples, and early intervention services. Multiples of America also assists researchers, physicians, educators, and other multiple-birth organizations worldwide in completing research.

Multiples of America maintains an archive of the results uncovered through the 134 research surveys conducted by the organization and a few outside researchers.

Multiples of America (also known as the National Organization of Mothers of Twins Clubs, Inc.) is a 501 (c) 3, non-profit organization dedicated to supporting families of multiple birth children through support, education, and research. For more information, click onto the website, http://www.multiplesofamerica.org.