Updating fetal foot length to gestational age references: a chart review of abortion cases from 2012 to 2014.

ABSTRACT

OBJECTIVES: We sought to develop an updated fetal foot length-to-gestational week reference range from patient-reported last menstrual period (LMP), ultrasound, and best-estimate for gestational age based on American College of Obstetricians and Gynecologists' (ACOG) pregnancy dating guidelines. Subsequently, we aimed to determine the impact, if any, of race/ethnicity on our findings and compare our measurements to commonly referenced ranges. METHODS: We performed a chart review of 610 dilation and evacuation records with gestational ages 14 weeks 0 days to 21 weeks 6 days from October 2012 to December 2014 in Honolulu, Hawaii. We analyzed records containing pathology-measured fetal foot length and three gestational age estimation methods using ANOVA tests, determined if race/ethnicity affected fetal foot length, and compared our measurements to previously published studies. RESULTS: Linear regression analysis demonstrated that ultrasound-derived gestational age dating provided the best-fit regression formula with an R-squared and adjusted R-squared value of 0.92. Patient body mass index (p=.15), parity (p=.15), and race (p=.99) did not affect the equation. Mean fetal foot length per gestational age differed from historically referenced ranges by 0.36-3.92 mm in either direction. CONCLUSIONS: Our population's fetal foot length per gestational age differed from ranges typically referenced by pathologists following abortion at all gestational ages, using all three methods of fetal gestational age estimation. As gestational age increased, the variability of fetal foot length measurements per gestational week increased. If post-abortion fetal foot length measurements are obtained, it is important to use an updated reference range. IMPLICATIONS Reference ranges frequently used by pathologists to assess fetal foot length following abortion may be outdated, limiting their utility. If facilities routinely obtain these measurements to estimate gestational age, it is important to use an updated reference range.