Estimation of fetal weight before and after amniotomy in the laboring gravid woman

Objective: This study was undertaken to search for differences between fetal weights estimated both ultrasonographically and clinically before and after amniotomy in laboring gravid women. Study Design: Estimates of fetal weight (ultrasonographic and clinical) were obtained for laboring gravid women before and after amniotomy. These estimates were compared with actual birth weights determined post partum. Results: One hundred sixty-two patients completed the study protocol. Comparisons made with unpaired Student t test analyses demonstrated a difference (P< .001) between ultrasonographically estimated fetal weights before and after amniotomy. Simple regression analysis showed a correlation between both ultrasonographic and clinical estimates of fetal weight and actual birth weights before and after amniotomy, with postamniotomy clinical estimates having the strongest correlation (ultrasonographic preamniotomy estimate, R = 0.717; ultrasonographic postamniotomy estimate, R = 0.630; clinical preamniotomy estimate, R = 0.742; and clinical postamniotomy estimate, R = 0.788). Of all ultrasonographic parameters measured, preamniotomy abdominal circumference correlated best with actual birth weight (R = 0.730). Conclusion: Clinical estimates of fetal weight after amniotomy correlated well with actual birth weights. Preamniotomy abdominal circumference was the ultrasonographic parameter best for prediction of actual birth weight. Maternal weight affected clinical but not ultrasonographic estimates of fetal weight in this study. However, clinical estimates of fetal weight were actually superior to ultrasonographic estimates of fetal weight in this study. (Am J Obstet Gynecol 2000;182:1117-20.)