PREDICTING FIRST-TRIMESTER SPONTANEOUS-ABORTION - RATIO OF MEAN SAC DIAMETER TO CROWN-RUMP LENGTH COMPARED TO EMBRYONIC HEART-RATE

First-trimester spontaneous abortions have been predicted from alterat ions in the gestational sac size and embryonic heart rate. To evaluate which parameter or combination of parameters has the greatest predict ive value, a prospective study tons carried out during the first trime ster of pregnancy. Pregnancy sac size, crown-rump length and heart rat e were measured in 603 embryos, of which 580 continued beyond 13 weeks ' gestation and 23 ended in first-trimester spontaneous abortions. Bas ed on the continuing pregnancies, rue constructed nomograms relating t he ratio of mean snc diameter to crown-rump length (S/CR) to gestation al age (last menstrual period [LMP]), to crown-rump length (CAL) and t o embryonic heart rate (EHR). The S/CR ratios of the 23 embryos that s pontaneously aborted in the first trimester were plotted on these nomo grams to determine the significance of val ties falling outside the 95 % confidence limits. Plotting the S/CR ratios of the aborted fetuses o n the S/CR versus LMP nomogram gave a sensitivity of 78.3%, a specific ity of 97.8% and a false-positive rate of 2.2%. The same population wa s evaluated for abortion risk using EHR nomograms, giving a sensitivit y. of 65.2%, specificity of 98.2% and false-positive rate of 1.8%. Our findings suggest that S/CR measurement in early pregnancy may be a si mple and reliable method of predicting first-trimester abortions.