Ultrasound Evaluation Versus Direct Measurement of Uterine Cavity Length: a Prospective Study

Levonogesterel (progestin only) IUDs have been used in the adult population for decades and due to their safety and efficacy are now successfully used in the nulliparous and adolescent population for menstrual regulation, dysmenorrhea, and contraception. IUDs have the highest continuation rate among teens of all forms of contraception at 12 months (86%). IUDs reduce menstrual flow by 90% 12 months post insertion, decrease menstrual cramp severity, and have greater than 99% effective contraception. All of this make IUDs an attractive option for our teens and their caregivers

At time of IUD insertion, a uterine sound is used to measure the cavity length. A sound is a rigid instrument that is placed inside the uterus to directly measure the uterine cavity length and is the standard first step prior to IUD insertion. The cavity length will ultimately determine the type and size of IUD that can be placed. Two manufacturers, Mirena ® and Sklya ® are currently being used in clinical practice. Mirena requires uterine cavity length between 6-10 cm and Sklya requires 4-8 cm length. To determine this length requires a pelvic exam and the use of uterine sound, however, approximately 50% of our patient population is unable to tolerate pelvic exams due to a variety of factors, such as developmental disabilities or pain. Thus, this requires patients to go under general anesthesia to have their IUD placed. The goal of this study is to determine if the actual uterine cavity length corresponds to the transabdominal measurement of the uterine cavity length.

Uterine size is largely under the influence of estrogen and as an adolescent progresses through puberty the dimensions of the uterus change. Given that a large portion of families seeking menstrual suppression & regulation present relatively close to menarche (mean age of 12.3 years old) there is a precedent for an institutional standard for pre-IUD insertion transabdominal ultrasound to ensure the uterus is of sufficient caliber

Prior research has focused on those undergoing intra-operative placement of a Mirena IUD. In one retrospective chart review of 56 adolescent patients with developmental disabilities, there was a 3.7% (2/56) failure rate of intra-operative IUD placement (abandoned IUD insertion in the operating room after anesthesia administration). One failure was due to the pelvimetry of the child and the other was due to a uterine cavity length of 4cm which was deemed insufficient for the Mirena IUD. In addition, two other patients had a uterus sound to less than 6 (5cm and 5.5cm) and Mirena was inserted anyways (Skyla was not available). About half of these patients had a pre-operative transabdominal US of the pelvis and the total uterine length was measured with an average length of 8.3cm. All uterine cavities were measured intra-op with an average length of 7.4cm.

Ultimately, all prior research has measured the length of the full uterus (uterine fundus, body of the uterus, and cervix) which is not representative of the measurement in question for IUD placement, the uterine cavity length. We propose a prospective cohort pilot study to compare transabdominal ultrasound measurements with uterine sound measurements to determine uterine cavity length. If these measures correlate, transabdominal US could be a validated pre-insertion tool for the physician and patient to avoid unnecessary anesthetic events and have appropriate IUDs available for insertion.