Saltus CW, Gatz J, Ritchey ME, Ichikawa LE, Armstrong MA, Alabster AL, Merchant M, Lynen R, Asiimwe A, Shi JM, Getahun DT, Xie F, Chiu VY, Anthony MS. Study of the association of uterine perforation and IUD expulsion with breastfeeding and postpartum timing at IUD insertion (APEX IUD) - study size estimation to actuality. Poster presented at the 35th Annual ICPE Conference; August 27, 2019. Philadelphia, PA. [abstract] Pharmacoepidemiol Drug Saf. 2019 Aug 20; 28(S2):748.

BACKGROUND: The FDA required a study to determine the extent to which breastfeeding and timing of postpartum intrauterine device (IUD) insertion practices in the United States (US) are associated with risk of uterine perforation and IUD expulsion. Uterine perforation is an uncommon event: 1.3 cases per 1,000 IUD insertions, based on a prospective European cohort of 61,448 women. Therefore, adequate sample size to assess this outcome was critical for study feasibility. A validation study was conducted to ensure adequate sample size, availability of breastfeeding data, and validation of outcome variables in four US health care systems (3 Kaiser Permanente sites—Northern California, Southern California, and Washington state—and Regenstrief Institute in Indiana) The validation study data accrual ended September 30, 2015.

OBJECTIVES: We present the approach to projecting sample size and the estimated and actual sample sizes in APEX IUD.

METHODS: The APEX IUD start of patient inclusion varies by site between January 1, 2001 and January 1, 2009; the end of patient accrual for all sites is April 30, 2018. The cohort and postpartum estimates for APEX IUD were based on the validation study’s findings of the total number of women aged ≤50 with IUD inserted after a minimum 12-month look-back, the number of women with IUD inserted within 52 weeks postpartum, and the percentage of those who had a postpartum insertion with breastfeeding status available. Projections to estimate APEX IUD sample size involved including 31 additional months of patient accrual beyond the validation study timeframe; and, based on the validation study’s results, estimating that 30% would have an IUD inserted within 52 weeks postpartum, and that 90% of those with an IUD insertion within 52 weeks postpartum would have breastfeeding data (exact percentages from validation study projected by site). The estimated and actual numbers of women in these categories are presented.

RESULTS: Based on results from the validation study, the estimated number of women in APEX IUD with an IUD insertion was 264,706, those with insertion within 52 weeks postpartum was 79,412 and with breastfeeding status available was 71,471. The actual numbers were 329,689, 98,576, and 95,529 respectively, about 25% higher than estimated.

CONCLUSIONS: The numbers in the validation study used to estimate sample sizes for the full-scale study provided a basis for study feasibility, but accounting for a higher trajectory of IUD use over time could have improved the projections.

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