Influence of maternal body mass index on the clinical estimation of fetal weight in term pregnancies

Nathan S. Fox, Vrunda Bhavsar, Daniel H. Saltzman, Andrei Rebarber, Stephen T. Chasen

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


OBJECTIVE:: To estimate the effect of maternal body mass index (BMI) on clinical estimated fetal weight in term pregnancies. METHODS:: We compared the clinical estimated fetal weight to the actual birth weight on 400 consecutive term pregnant patients admitted for delivery. We then evaluated whether the maternal BMI was significantly associated with the clinical estimated fetal weight accuracy in estimating birth weight. Patients with singleton pregnancies at 37-42 weeks of gestation were included. Patients with an ultrasound-estimated fetal weight within 3 weeks of admission were excluded. Estimated fetal weight accuracy was defined as the absolute error (absolute value of estimated fetal weight minus birth weight) and absolute percent error (absolute error divided by birth weight multiplied by 100). The primary outcome was an absolute percent error of less than 10% (ie, an estimated fetal weight within ±10% of the birth weight). RESULTS:: The proportion of clinical estimated fetal weights within ±10% and within ±20% of the birth weight significantly decreased with increasing BMI categories (χ for trend P=.040 and 0.020, respectively). Clinical estimated fetal weights obtained in women with BMI at or greater than 30 were significantly less likely to be within ±10% of the birth weight when compared with women with a BMI less than 25 (66.4% compared with 82.5%, P=.011). Body mass index was significantly positively associated with the absolute error (P=.046) and the absolute percent error (P=.011), even after controlling for birth weight. CONCLUSION:: Increased maternal BMI is significantly associated with decreased clinical estimated fetal weight accuracy.

Original languageEnglish
Pages (from-to)641-645
Number of pages5
JournalObstetrics and Gynecology
Issue number3
StatePublished - Mar 2009


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