I inserted an etonogestrel implant (Implanon®) in a woman on what we thought was Day 1 of her first menstrual cycle following a miscarriage. She did not continue to bleed after that day, which was notably different to her usual menstrual loss. She next presented 35 days later requesting removal of her implant because she was pregnant. As she was happy to continue with the pregnancy her implant was removed and she went on to deliver a healthy child.

Her general practitioner clarified that 22 days prior to the insertion an ultrasound scan (USS) showed a gestational sac with uncertain viability. A repeat USS 12 days before insertion showed no evidence of pregnancy, a pregnancy test was negative and complete miscarriage was diagnosed. After removal of the implant a dating USS confirmed a single, viable pregnancy estimated at 13 weeks' gestation. Only 13 weeks and 1 day had lapsed since the first USS showing a gestational sac.

Looking at the time between insertion of the implant and the dating USS this case represents the unusual situation of an implant being inserted when someone is already pregnant rather than a true failure of the device. An assumption was made that new vaginal bleeding 3 weeks after a miscarriage was Day 1 of her menstrual cycle.

The current Faculty guidance1 recommends that “ideally, an implant should be inserted between Days 1 and 5 (inclusive) of a normal menstrual cycle. No additional contraception is required”. Following miscarriage it can be inserted up to Day 5 with no additional contraception required. If the method is started on what is assumed to be Day 1 and they have been advised that there may be alterations to their bleeding pattern clients would not necessarily be concerned if they did not continue to bleed as normal for that menstruation. This could have been a late presentation of pregnancy if the abnormal menstruation and pregnancy symptoms were mistakenly thought to be side effects of the implant. This also applies to other hormonal methods initiated on Day 1 of a menstrual cycle.

It can be difficult to define on which day a miscarriage has occurred, particularly if the patient has not sought medical assistance or you do not have access to medical records and test results. This causes difficulty in deciding when to insert the device if sexual intercourse has already occurred. Assuming this patient's usual 28-day cycle, conception appears to have occurred within a few days of the second USS, which showed no evidence of pregnancy.

Delaying initiation of hormonal methods until Day 2 of a menstrual cycle would decrease the likelihood of mistaking abnormal vaginal bleeding for a period. However, this would also decrease the number of days available without additional precautions being required. An alternative would be to advise a pregnancy test 3 weeks after insertions performed on Day 1 if the period is significantly shorter than usual. This would be particularly useful for the first menstruation after a miscarriage or termination of pregnancy when there has been unprotected sexual intercourse.