IND approval from FDA was rejected and IRB approval was never granted.

Short-interval pregnancy (SIP) or rapid, repeat pregnancy is defined as a pregnancy within one year of prior delivery. These pregnancies are often unintended and are associated with adverse risks. Low contraceptive initiation during the postpartum period is a contributing factor to SIP. This study will be the first to investigate the initiation of a highly-effective, immediately active contraceptive device during the antepartum period. The antepartum period serves as an ideal time for postpartum contraception counseling, due to patients' active involvement with the healthcare system. The pharmacokinetic analysis proposed in this study will be the first to investigate whether and to what extent ENG hormone crosses the placenta. This data will enrich understanding of the pharmacology of exogenous progestins administered during pregnancy and provide information that can be incorporated into future patient counseling regarding the risks of fetal exposure with exogenous progestin use.

Inclusion Criteria:

• Pregnant women (ages 18-34 years) ≥37 weeks gestational age who are interested in using an ENG contraceptive implant for their postpartum birth control method.
• Women with a history of at least one uncomplicated vaginal delivery at term who have received routine prenatal care (at least five visits) including an anatomy ultrasound with confirmed dating.

Exclusion Criteria:

• Women outside the gestational age outlined above.
• Women who are seen outside of the enrolling clinics.
• Women 35 years and older at the time of anticipated delivery, as these women meet the clinical definition of advanced maternal age which has been associated with increased adverse events in pregnancy.
• Women with any condition that necessitates a medically indicated delivery (e.g. diabetes mellitus, any hypertensive disorder), multiple gestations, fetal anomalies, Class III obesity (body mass index >40), concurrent use of either an injectable or vaginal progestin, and any concerns related to ENG implant use based on the US Medical Eligibility Criteria for Contraceptive Use (defined as a class 3 or 4 recommendation).

We are only enrolling women in this study as we are studying the acceptability of a contraceptive device during pregnancy and so this study is not appropriate for men.