Media Advisory
Monday, April 7, 2025
The NIH findings could lead to more effective monitoring of twin pregnancies.
What
Twins, who are smaller at birth on average than singleton twins, begin pregnancy smaller than previously thought, according to a study conducted by researchers at the National Institutes of Health (NIH). The ultrasound study revealed that twins have less fat tissue and less muscle mass than singleton twins starting at 15 weeks of pregnancy. If confirmed by further research, the findings could provide information to guide doctors in monitoring and managing twin pregnancies.
The researchers analyzed data from ultrasound studies previous studies on fetal development in the womb. The analysis included 3D ultrasounds of 2,604 singleton pregnancies and 315 twins. All twin pairs had individual placentas. Twin pairs who shared a placenta were not included in the analysis.
From 15 weeks onwards, thigh volume was significantly smaller for twins than for singleton twins. Twins had smaller thigh fat and lean volumes than singleton twins. They also had a lower thigh fat-to-lean ratio than singleton twins, with a proportional reduction of 2.7 to 4.2 % in fat between 15 and 37 weeks. Previous studies of in utero twin growth involved 2D ultrasounds and had documented decreased growth in twins compared to singleton twins only in the early 3e trimester (28 to 40 weeks).
Scientists do not believe that the twins' early small size is the result of increased competition for nutrients, as their placentas should have been sufficiently developed to provide the necessary resources until the third trimester. Instead, they hypothesize that the twins' small size early in pregnancy may be an adaptation to meet the increased resource needs of both fetuses later in pregnancy.
The study was led by Jessica Gleason, Ph.D., and Katherine Grantz, MD, of the Eunice Kennedy Shriver National Institute of Child Health and Human Development. of the NIH, and their colleagues. It is published in JAMA Pediatrics .Who
Jessica Gleason, Ph.D., perinatal epidemiologist, is available for comment.
Article
Gleason JL, et al. Fetal body composition in twins and singleton babies.
JAMA Pediatrics. DOI: https://doi.org/10.1001/jamapediatrics.2025.0116 (2025) About
Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) : NICHD conducts research and training to understand human development, improve reproductive health, enrich the lives of children and adolescents, and maximize the capabilities of all. For more information, visithttps://www.nichd.nih.gov .About the National Institutes of Health (NIH):
The NIH, the nation's medical research agency, comprises 27 institutes and centers and is a component of the U.S. Department of Health and Human Services. The NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research. It studies the causes, treatments, and cures for common and rare diseases. For more information about the NIH and its programs, visit www.nih.gov .NIH…Transforming Discovery into Health
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