A Simple Clinical Formula for Predicting Fetal Weight in Labour at Term–Derivation and Validation (Original Articles) (Report)

A Simple Clinical Formula for Predicting Fetal Weight in Labour at Term--Derivation and Validation (Original Articles) (Report)

A Simple Clinical Formula for Predicting Fetal Weight in Labour at Term--Derivation and Validation (Original Articles) (Report)

Clinicians frequently estimate fetal weight when examining women in labour at term. This may help in predicting cephalopelvic disproportion when labour progress is poor, (1) or give early warning of possible shoulder dystocia. (2) In experienced hands, intrapartum clinical estimates of birth weight for term infants are at least as good as ultrasound-based predictions, being correct to within 10% of the birth weight in 55-72% of estimations. (3-10) A more objective estimate of fetal weight may be offered by measurement of symphysis-fundal height (SFH) using a tape measure. (11-13) This requires minimal experience, relying only on identifying the upper edge of the pubic symphysis and the highest point on the uterus. However, there is no simple formula that converts SFH measurement into fetal weight. The Johnson formula is frequently quoted, where birth weight in g=(SFH in cm-13) x 155, with further adjustments based on maternal obesity and engagement of the fetal head. (12) A South African study found good correlation of intrapartum SFH measurement with birth weight (r=0.56), and derived a regression equation, but the authors stated that the derived formula was ‘not sufficiently accurate to be clinically useful’. (14) A problem with fetal weight estimation is that all methods are least accurate at extremes of birth weight. (15-17) Macrosomia (birth weight of 4 000 g and above) is notoriously difficult to predict. (2,18,19) Where a formula is inaccurate at the upper extreme of birth weight, the most useful tool may be a cut-off measure of SFH to assist prediction of macrosomia. This study was done to derive and validate a simple formula for birth weight based on SFH, and to determine a useful SFH cut-off value for prediction of fetal macrosomia (birth weight [greater than or equal to]4 000 g). Methods

A Simple Clinical Formula for Predicting Fetal Weight in Labour at Term--Derivation and Validation (Original Articles) (Report)

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