Fetal Body Composition in Twins and Singletons.
Jessica L Gleason1, Wesley Lee2, Zhen Chen3
1Epidemiology Branch, Division of Population Health Research, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland.
JAMA Pediatrics
|April 7, 2025
Summary
Twin fetuses show reduced fat tissue accumulation compared to singletons, suggesting an early evolutionary adaptive process. This difference in fetal growth is evident from 15 weeks gestation.
Area of Science:
- Fetal Development
- Comparative Anatomy
- Evolutionary Medicine
Background:
- Third-trimester fetal growth deceleration in twin pregnancies is increasingly viewed as an evolutionary adaptation.
- Understanding differential growth trajectories between twins and singletons requires evaluating soft-tissue development.
Purpose of the Study:
- To compare the longitudinal growth of lean and fat tissue in twin versus singleton fetuses throughout pregnancy.
Main Methods:
- A prospective cohort study involving dichorionic twins and singletons.
- Serial ultrasound scans were used to track fetal growth and measure fetal volume for tissue analysis.
- Data were collected from 12 US clinical centers between 2009-2019, with analysis from 2023-2024.
Main Results:
- Twin fetuses exhibited significantly smaller abdominal measurements and subcutaneous tissue thickness compared to singletons from 25 to 37 weeks gestation.
- Fractional thigh volumes (total, fat, and lean) were consistently smaller in twins starting from 15 weeks gestation.
- Twins demonstrated a proportionally lower fat percentage throughout gestation, with a 2.7% to 4.2% reduction compared to singletons.
Conclusions:
- Twin fetuses accumulate proportionally less fat tissue in utero compared to singletons, beginning as early as 15 weeks gestation.
- These findings support the hypothesis of an early evolutionary adaptive process influencing fetal growth in uncomplicated dichorionic twin pregnancies.
- The consistent observation of smaller sizes and reduced fat accumulation in twins underscores adaptive mechanisms in response to in utero conditions.
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