Crude incidence rate was calculated as the number of outcomes occurring during the person-time at risk divided by the total person-time at risk (in person-years)

Women who were within 52 weeks postpartum and were or were not breastfeeding at the time of IUD insertion

Crude estimates of the cumulative incidence, defined as number of outcomes occurring up to a time point out of the number of IUD insertions

Women who were within 52 weeks postpartum and were or were not breastfeeding at the time of IUD insertion

Propensity score-adjusted hazard ratio to evaluate whether the risk of uterine perforation among women who were breastfeeding at the time of first observed IUD insertion differs from the risk of uterine perforation among women who were not breastfeeding at the time of first observed IUD insertion

Women who had given birth in the previous 52 weeks and had breastfeeding status "yes" or "no" were included in this analysis

Crude incidence rate was calculated as the number of outcomes occurring during the person-time at risk divided by the total person-time at risk (in person-years)

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Crude estimates of the cumulative incidence, defined as number of outcomes occurring up to a time point out of the number of IUD insertions

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Adjusted for propensity scores and breastfeeding status, to evaluate whether the risk of uterine perforation among women who had a first observed IUD insertion within different time periods postpartum differs from the risk of uterine perforation among women who had their first observed IUD insertion more than 52 weeks postpartum, including women without a recorded delivery within the past 52 weeks. Reference group: IUD insertion > 52 weeks postpartum

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Adjusted for propensity scores and breastfeeding status, to estimate the risk of uterine perforation among women who had a first observed IUD insertion early in the postpartum period (i.e., up to 14 weeks postpartum) versus those who had a first observed IUD insertion late in the postpartum period (i.e., more than 14 weeks postpartum, including women without recorded delivery within the past 52 weeks). Reference group: IUD insertion >14 weeks postpartum or with no recorded delivery

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Adjusted for propensity scores and breastfeeding status, to estimate the risk of uterine perforation among women who had a first observed IUD insertion ≤ 36 weeks postpartum versus women who had a first observed IUD insertion > 36 weeks postpartum, including women without recorded delivery within the past 52 weeks. Reference group: IUD insertion >36 weeks postpartum or with no recorded delivery

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Adjusted for propensity score, overall and stratified by breastfeeding status at the time of IUD insertion for ≤ 36 weeks postpartum at IUD insertion versus > 36 weeks postpartum or with no recorded delivery, at 1 year and 5 years of follow-up. Reference group: > 36 weeks or no delivery

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Propensity score-adjusted incidence rate differences (per 1,000 person-years) for uterine perforation for women ≤ 36 weeks postpartum at IUD insertion compared with those who were > 36 weeks postpartum or with no recorded delivery, 1 year of follow-up and 5 years of follow-up, overall and stratified by breastfeeding status. Reference group: > 36 weeks or no delivery

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Crude incidence rate was calculated as the number of outcomes occurring during the person-time at risk divided by the total person-time at risk (in person-years)

Women with either LNG-IUD (levonorgestrel-releasing intrauterine system) or copper IUD insertions

Crude estimates of the cumulative incidence, defined as number of outcomes occurring up to a time point out of the number of IUD insertions

Women with either LNG-IUD (levonorgestrel-releasing intrauterine system) or copper IUD insertions

Propensity score-adjusted hazard ratio to evaluate whether the risk of uterine perforation among women with LNG-releasing IUD at the time of first observed IUD insertion differs from the risk of uterine perforation among women with copper IUD at the time of first observed IUD insertion

Women with either LNG-IUD (levonorgestrel-releasing intrauterine system) or copper IUD insertions

Crude incidence rate was calculated as the number of outcomes occurring during the person-time at risk divided by the total person-time at risk (in person-years)

Women with menorrhagia (heavy menstrual bleeding) status (yes/no) in the 12 months before IUD insertion

Crude estimates of the cumulative incidence, defined as number of outcomes occurring up to a time point out of the number of IUD insertions

Women with menorrhagia (heavy menstrual bleeding) status (yes/no) in the 12 months before IUD insertion

Propensity score-adjusted hazard ratio to evaluate whether the risk of uterine perforation among women using an IUD who have at least one diagnosis code indicating menorrhagia in the 12 months before IUD insertion differs from the risk of uterine perforation among women who do not have this indication

Women with menorrhagia (heavy menstrual bleeding) status (yes/no) in the 12 months before IUD insertion

Propensity score-adjusted hazard ratios to evaluate the extent to which breastfeeding status (yes vs. no) modified the association of uterine perforation for women with IUD insertion at different time periods postpartum (i.e., IUD insertion ≤ 14 weeks versus IUD insertion > 14 weeks postpartum) among women with a recorded delivery within the past 52 weeks at the time of the first observed IUD insertion

Women who had given birth in the previous 52 weeks and had breastfeeding status "yes" or "no" were included in this analysis

Propensity score-adjusted hazard ratios to evaluate the extent to which type of IUD (LNG-IUD vs. copper IUD) modified the association between uterine perforation and breastfeeding among women who were and were not breastfeeding at the time of first observed IUD insertion

Women who had given birth in the previous 52 weeks and had breastfeeding status "yes" or "no" were included in this analysis

Adjusted for propensity score and breastfeeding status, to evaluate the extent to which type of IUD (LNG-IUD vs. copper IUD) modified the association between uterine perforation and postpartum timing of IUD insertion for women with IUD insertion at different time periods postpartum (i.e., ≤ 6 weeks, > 6 and ≤ 14 weeks, > 14 and ≤ 52 weeks) versus IUD insertion more than 52 weeks postpartum, including no recorded delivery within the past 52 weeks, at the time of the first observed IUD insertion. Reference group: LNG-IUD or Copper IUD, > 52 weeks or no delivery

Women with either LNG-IUD (levonorgestrel-releasing intrauterine system) or copper IUD insertions

Crude incidence rate was calculated as the number of outcomes occurring during the person-time at risk divided by the total person-time at risk (in person-years)

Women who were within 52 weeks postpartum and were or were not breastfeeding at the time of IUD insertion

Crude estimates of the cumulative incidence, defined as number of outcomes occurring up to a time point out of the number of IUD insertions

Women who were within 52 weeks postpartum and were or were not breastfeeding at the time of IUD insertion

Propensity score-adjusted to evaluate whether the risk of IUD expulsion among women who were breastfeeding at the time of first observed IUD insertion differs from the risk of IUD expulsion among women who were not breastfeeding at the time of first observed IUD insertion

Women who had given birth in the previous 52 weeks and had breastfeeding status "yes" or "no" were included in this analysis

Crude incidence rate was calculated as the number of outcomes occurring during the person-time at risk divided by the total person-time at risk (in person-years)

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Crude estimates of the cumulative incidence, defined as number of outcomes occurring up to a time point out of the number of IUD insertions

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Adjusted for propensity score and breastfeeding status, to evaluate whether the risk of IUD expulsion before and after 49 days of insertion among women who had a first observed IUD insertion within different time periods postpartum differs from the risk of IUD expulsion among women who had their first observed IUD insertion more than 52 weeks postpartum, including women without a recorded delivery within the past 52 weeks Reference group: IUD insertion > 52 weeks postpartum

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Adjusted for propensity scores, to estimate the risk of IUD expulsion among women who had a first observed IUD insertion early in the postpartum period (i.e., up to 14 weeks postpartum) versus those who had a first observed IUD insertion late in the postpartum period (i.e., more than 14 weeks postpartum, including women without recorded delivery within the past 52 weeks). Reference group: IUD insertion >14 weeks postpartum or with no recorded delivery

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Adjusted for propensity scores, to estimate the risk of IUD expulsion among women who had a first observed IUD insertion ≤ 36 weeks postpartum versus women who had a first observed IUD insertion > 36 weeks postpartum, including women without recorded delivery within the past 52 weeks. Reference group: IUD insertion >36 weeks postpartum or with no recorded delivery

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Overall and stratified by breastfeeding status at the time of IUD insertion for IUD expulsion for ≤ 36 weeks postpartum at IUD insertion versus > 36 weeks postpartum or with no recorded delivery, at 1 year and 5 years of follow-up Reference group: > 36 weeks or no delivery

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Adjusted incidence rate differences (per 1,000 person-years) for IUD expulsion for women ≤ 36 weeks postpartum at IUD insertion compared with those who were > 36 weeks postpartum or with no recorded delivery, 1 year of follow-up and 5 years of follow-up, overall and stratified by breastfeeding status Reference group: > 36 weeks or no delivery

Women with first observed IUD insertions at different postpartum timing or women without recorded delivery within the past 52 weeks

Crude incidence rate was calculated as the number of outcomes occurring during the person-time at risk divided by the total person-time at risk (in person-years)

Women with either LNG-IUD (levonorgestrel-releasing intrauterine system) or copper IUD insertions

Crude estimates of the cumulative incidence, defined as number of outcomes occurring up to a time point out of the number of IUD insertions

Women with either LNG-IUD (levonorgestrel-releasing intrauterine system) or copper IUD insertions

Propensity score adjusted to evaluate whether the risk of IUD expulsion among women with LNG-releasing IUD at the time of first observed IUD insertion differs from the risk of IUD expulsion among women with copper IUD at the time of first observed IUD insertion

Women with either LNG-IUD (levonorgestrel-releasing intrauterine system) or copper IUD insertions

Crude incidence rate was calculated as the number of outcomes occurring during the person-time at risk divided by the total person-time at risk (in person-years)

Women with menorrhagia (heavy menstrual bleeding) status (yes/no) available in the 12 months before IUD insertion

Crude estimates of the cumulative incidence, defined as number of outcomes occurring up to a time point out of the number of IUD insertions

Women with menorrhagia (heavy menstrual bleeding) status (yes/no) available in the 12 months before IUD insertion

Propensity score adjusted to evaluate whether the risk of IUD expulsion among women using an IUD who have at least one diagnosis code indicating menorrhagia in the 12 months before IUD insertion differs from the risk of IUD expulsion among women who do not have this indication

Women with menorrhagia (heavy menstrual bleeding) status (yes/no) available in the 12 months before IUD insertion

Propensity score-adjusted hazard ratios to evaluate the extent to which type of IUD (LNG-IUD vs. copper IUD) modified the association between IUD expulsion and breastfeeding among women who were and were not breastfeeding at the time of first observed IUD insertion

Women who had given birth in the previous 52 weeks and had breastfeeding status "yes" or "no" were included in this analysis

Adjusted for propensity score and breastfeeding status, to evaluate the extent to which type of IUD (LNG-IUD vs. copper IUD) modified the association between IUD expulsion and postpartum timing of IUD insertion for women with IUD insertion at different time periods postpartum (i.e., ≤ 6 weeks, > 6 and ≤ 14 weeks, > 14 and ≤ 52 weeks) versus IUD insertion more than 52 weeks postpartum, including no recorded delivery within the past 52 weeks, at the time of the first observed IUD insertion. Reference group: LNG-IUD or Copper IUD, > 52 weeks or no delivery

Women with either LNG-IUD (levonorgestrel-releasing intrauterine system) or copper IUD insertions

To describe the prevalence of indicators of a difficult IUD insertion (e.g., need for cervical dilation, ultrasound guidance, paracervical block, clinician not indicating difficulty, use of misoprostol among all users)

Women with first observed IUD insertions

To describe the prevalence of indicators of a difficult IUD insertion (e.g., need for cervical dilation, ultrasound guidance, paracervical block, clinician not indicating difficulty, use of misoprostol among all users)

Women with first observed IUD insertions