An ultrasound-based fetal weight reference for twins

Area of Science:

• Maternal-fetal medicine
• Prenatal diagnostics
• Twin pregnancy research

Background:

• Accurate fetal weight estimation is crucial for monitoring twin pregnancies.
• Existing fetal weight charts often lack stratification by chorionicity, limiting their utility for twins.
• Twin pregnancies present unique growth patterns that necessitate specific reference standards.

Purpose of the Study:

• To construct an ultrasound-based estimated fetal weight-for-gestational-age reference specifically for twin fetuses.
• To stratify these references by chorionicity (monochorionic vs. dichorionic) to account for differing growth trajectories.
• To provide an improved tool for assessing fetal growth in twin pregnancies.

Main Methods:

• Retrospective cohort study of live-born, nonanomalous twins delivered after 34 weeks.
• Fetal weight estimated using ultrasound biometry and Hadlock's formula.
• Multilevel linear regression models used to adjust for twin pregnancy clustering and serial measurements; smoothed percentile curves generated.

Main Results:

• 642 twin fetuses and 3078 ultrasound observations were analyzed; 16% were monochorionic.
• Fetal growth accelerated in the second trimester and showed linear progression in the third.
• Median weight for monochorionic twins was consistently lower than for dichorionic twins.

Conclusions:

• The developed reference values address limitations of current charts, offering a superior tool for twin fetal growth assessment.
• Dichorionic twins deviated from singleton references around 32 weeks gestation.
• Monochorionic twins deviated from singleton references earlier, around 28 weeks gestation.