First-Trimester Cell-Free DNA Fetal Fraction and Birth Weight in Twin Pregnancies

Area of Science:

• Maternal-Fetal Medicine
• Genetics
• Obstetrics

Background:

• The relationship between cell-free DNA (cfDNA) fetal fraction and birth weight in twin gestations is not well understood.
• First-trimester cfDNA screening is widely used for aneuploidy detection in pregnancies.

Purpose of the Study:

• To investigate the association between first-trimester cfDNA fetal fraction and birth weight below the 10th percentile in twin gestations.
• To determine if extreme fetal fraction values (low or high) correlate with impaired fetal growth in twins.

Main Methods:

• A secondary analysis of the Twin cfDNA Study, a retrospective cohort of 1,041 twin pregnancies.
• Comparison of birth weights between pregnancies with normal, low (<5%), and high (>95%) cfDNA fetal fractions.
• Univariable and multivariable regression analyses were used, adjusting for potential confounders.

Main Results:

• No significant difference in median fetal fraction was observed between twins with birth weight <10th percentile and those with normal birth weight (≥10th percentile).
• No association was found between high or low fetal fraction and birth weight <10th percentile or <5th percentile for one or both twins.
• Results remained consistent after adjusting for confounding factors such as chronic hypertension, elevated BMI, and race.

Conclusions:

• Extremes in first-trimester cfDNA fetal fraction are not associated with birth weight below the 10th percentile in twin gestations.
• First-trimester fetal fraction does not appear to be a predictor of impaired fetal growth in twin pregnancies.
• These findings contrast with observations in singleton pregnancies, highlighting a potential difference in the utility of fetal fraction for growth assessment between singleton and twin gestations.