USOs were instances of sexual intercourse where neither partner utilized any form of contraception. Participants were assessed using Timeline Follow-Back (TLFB), a calendar assisted structured interview that provided a way to cue memory so that accurate recall was enhanced for event-level data. TLFB has been used to assess sexual risk-taking. Participants were asked to provide the number of USOs experienced 90 days prior to baseline assessment, between baseline assessment and 2-month follow up, and from 2-month follow up to 6-month follow up.

Some participants did not attend the 2-month or 6-month assessments.

Alcohol use was measured by the TLFB. Participants were asked if they had consumed any standard alcoholic drinks 90 days prior to baseline assessment, between baseline assessment and 2-month follow up, and from 2-month follow up to 6-month follow up. Participants' responses could only be Yes or No. Results reflect the participants who responded Yes.

Some participants did not attend the 2-month or 6-month assessments.

Cannabis use was measured by the TLFB. Participants were asked if they had used or consumed any cannabis 90 days prior to baseline assessment, between baseline assessment and 2-month follow up, and from 2-month follow up to 6-month follow up. Participants' responses could only be Yes or No. Results reflect the participants who responded Yes.

Some participants did not attend the 2-month or 6-month assessments.

STIs were measured using urine samples or home vaginal swabs testing kits, which were collected at the baseline assessment and 6 weeks postpartum. Results reflect participants whose results came back with positive results for any STI.

Not all participants provided a urine sample or home vaginal swab for testing due to a national shortage on STI tests during the COVID-19 pandemic.

USOs were instances of sexual intercourse where neither partner utilized any form of contraception. Participants were assessed using Timeline Follow-Back (TLFB), a calendar assisted structured interview that provided a way to cue memory so that accurate recall was enhanced for event-level data. TLFB has been used to assess sexual risk-taking. Participants were asked to provide the number of USOs experienced from the period of birth up to 6 weeks postpartum.

Not all participants participated in the postpartum follow-up assessment.

Birth weight of participants' babies was measured in grams.

Birth weight data was collected from EMRs at the participating sites, regardless of whether the participant completed the 6 Weeks Post Partum visit or not, which is why the Overall Number of Participants Analyzed is different than the Participant Flow. Data from some participants could not be collected because it was missing from the EMR or the participant did not consent to the release of the information. Additionally, data from twins was not included to avoid confounding the results.

Head circumference of participants' babies was measured in centimeters.

Birth head circumference data was collected from EMRs and paper records, regardless of whether the participant completed the 6 Weeks Post Partum visit or not, which is why the Overall Number of Participants Analyzed is different than the Participant Flow. Data from some participants could not be collected because it was missing from the EMR or the participant did not consent to the release of the information. Additionally, data from twins was not included to avoid confounding the results.

Birth length of participants' babies was measured in centimeters.

Birth length data was collected from EMRs and paper records, regardless of whether the participant completed the 6 Weeks Post Partum visit or not, which is why the Overall Number of Participants Analyzed is different than the Participant Flow. Data from some participants could not be collected because it was missing from the EMR or the participant did not consent to the release of the information. Additionally, data from twins was not included to avoid confounding the results.

Heavy episodic drinking was defined as consumption of 4 or more standard alcoholic drinks during a single day. Participants were asked if they had engaged in any heavy episodic drinking 90 days prior to baseline assessment and from the period from birth to 6 weeks postpartum. Participants' responses could only be Yes or No. Results reflect the participants who responded Yes.

Not all participants participated in the postpartum follow-up assessment.

Cost-effectiveness was measured in US dollars (USD) and was evaluated as the incremental cost-effectiveness ratio (ICER) that considers the difference in the mean total costs and the difference in health outcomes and events between the two arms. Results reflect the cost-effectiveness evaluation based on estimated costs per case of unprotected sexual occasion averted, alcohol or illicit drug use averted, and sexually transmitted infection (STI) event averted. To develop a plausible full range, a 25% variation of the estimated mean in each arm was used. All participants who were randomized were included in the analysis for this outcome measure.