Comparing preoperative dating and postoperative dating for second-trimester surgical abortions

Abstract

Objectives: To assess relationships between preoperative and postoperative dating of second-trimester surgical abortion.

Study design: We used a deidentified institutional database to extract demographic, dating and pathology data for surgical abortions performed at 14 to 23-6/7 weeks' gestational age (GA) from 9/2015 to 5/2017. We excluded women with multiple gestations, fetal anomalies and missing fetal biometric measurements. We assigned preoperative GA by ultrasonography for unknown last menstrual period (LMP) or when discrepancy between sonographic and LMP dating exceeded 7 days (<15-6/7 weeks), 10 days (16 to 21-6/7 weeks) or 14 days (22 to 23-6/7 weeks). We determined postoperative GA using fetal foot length pathology standards published by Streeter in 1920 and Drey et al. in 2005. We performed regression analysis to estimate the relationship between pre- and postoperative estimates of GA and to assess demographic effects on these estimates, and χ² tests to assess whether fetal foot lengths were concordant with, larger than or smaller than the expected range for the preoperative GA.

Results: The 469 patients analyzed had a median preoperative GA of 19-4/7 weeks (range 14-0/7 to 23-6/7 weeks). Preoperative dating highly correlated with postoperative dating using both pathology standards (r²=0.95, p<.001), without any clinically relevant effect by body mass index (Streeter and Drey, p=.79), parity (Streeter p=.89; Drey p=.71), race (Streeter p=.06; Drey p=.07) or GA. Fetal foot lengths were larger than expected in 134 (28.6%) women using Streeter and 17 (3.6%) women using Drey standards (p<.001).

Conclusions: Preoperative dating and postoperative dating for second-trimester surgical abortion highly correlate. Use of Streeter standards results in more women with a postoperative GA greater than expected compared to Drey standards.

Implications: Increasing legal gestational age restrictions have placed additional burden on clinicians providing safe abortions, but guidelines on gestational age determination are lacking. Contemporary pathology standards consistent with modern practice and universally accepted by abortion providers and gynecologic pathologists are critical to our goal of safe and legal abortion provision.

Keywords: Abortion; Fetal foot length; Gestational age; Postnatal foot length; Pregnancy; Ultrasound.

Fig. 1.

Scatterplot comparing gestational age by preoperative and postoperative assessments in women undergoing second-trimester surgical abortion.(A) Streeter pathology standards [7].(B) Drey pathology standards [8].Fetal age by preoperative gestational age (weeks) versus postoperative gestational age (weeks), R²=0.95, p<.001 for both graphs. Preoperative gestational age was based on LMP or sonographic dating in cases of unknown LMP or when the discrepancy between sonographic and LMP dating exceeded 7 days (<15-6/7 weeks’ GA), 10 days (16 to 21-6/7 weeks’ GA) or 14 days (22 to 23-6/7 weeks’ GA) [5].