Ultrasonographic measurement of crown-rump length in high-order multifetal pregnancies

The objective of the study was to evaluate the crown-rump length (CRL) in high-order multifetal pregnancies (three or more fetuses). The records of patients who underwent multifetal pregnancy reduction were reviewed. The following parameters were defined: the mean CRL (CRL(MEAN)) and the difference between the largest and smallest CRL (CRL(RANGE)) for each pregnancy. CRL(MEAN) was plotted versus gestational age (GA) and the line of best fit was derived. The residual for each CRL (CRL(RES)) was calculated by subtracting the value predicted by the regression line from the individual CRL (CRL(IND)). Regression lines for single tons with confirmed GA from four previously reported studies were used for comparison. A total of 82 patients were included (29 triplets, 38 quadruplets and 15 quintuplets; mean GA 10.7 ± 0.78 weeks). CRL(MEAN) correlated with GA (CRL(MEAN) = 38.88 - 8.78 (GA) + 0.82 (GA)²; R = 0.83; R² = 0.70). This second-degree polynomial remained within the range for singletons. No significant differences in maternal age, GA and CRL(MEAN) were noted between the patients with different numbers of fetuses. The median CRL(RANGE) was largest in quintuplets, followed by quadruplets and triplets. The CRL(RANGE) correlated poorly with GA. The mean CRL in multifetal pregnancies Increases with GA similarly to that in singletons. The variability of individual measurements increases with the number of fetuses and CRLs are lower in quintuplets.