Triplet Ultrasound Growth Curves Mapped

The identification of abnormal growth in triplet fetuses has been difficult because there have been no standards for comparison. A study at Tufts-New England Medical Center in Boston has produced curves for growth as measured by estimated fetal weight, abdominal circumference, biparietal diameter, head circumference, and femur length. All measurements were conducted sonographically.

A research team led by Neeta Raghavan, MD, reviewed records of all triplets managed in a single tertiary center from 1992 to 2004. Fetuses with major anomalies, prior selective reduction, or fetal demise were excluded. Data from the earliest and latest weeks of gestation for which there were fewer than 30 fetal measurements were also excluded. The newly-derived curves reflect data for weeks 14 to 34.

The group used multilevel models (also referred to as random effects or mixed models) to account for variation in growth within a single fetus, variations in growth between multiple fetuses within a single mother, and variations in fetal growth between different mothers. Curves were constructed on the 10th, 50th, and 90th percentiles using 1,451 sonograms, 368 fetuses, and 123 total pregnancies.

Distribution of fetal weight shows three similar curves between 14 and 34 weeks. At 14 weeks, median weight at the 10th percentile is 79 g, at the 50th percentile 100 g, and 126 g at the 90th percentile. At 34 weeks, the median weights are 1853 g, 2077 g, and 2431 g respectively.

Raghavan NL, Ruthazer R, House M, Chelmow D. Triplet ultrasound growth parameters. Obstet Gynecol. 2005;105(4)suppl:52S.