Objective: To estimate the width of the normal uterine cavity at the fundus and evaluate its relationship to parity, gravidity, prior cesarean delivery, uterine volume, and patient age.
Methods: From September 1, 2009, to November 10, 2009, all premenopausal patients aged 50 years or younger who had a normal uterus by ultrasonography were included in the study. Standard measurements of the outer aspect of the uterus as well as two three-dimensional volumes of the uterus (one transverse and the other longitudinal) were done at the time of the scan. These volumes were manipulated retrospectively to obtain the coronal view of the uterine cavity. Using electronic calipers on the picture archiving and communication system, a network with a server that stores electronic images in an ultrasonography or imaging practice, the width of the uterine cavity was measured on each volume. The width of the uterine cavity was then correlated with patient gravidity, parity, previous cesarean delivery, calculated uterine volume, endometrial echo, and age.
Results: The width of the uterine cavity enlarges significantly with increasing gravidity or parity. The width of the uterine cavity ranged from a mean of 27 mm in nulliparous women to 32 mm in those with more than one pregnancy. There was a strong correlation between the width of the uterine cavity and the overall uterine volume as well as width of the endometrial echo (P<.001). There was no appreciable relationship between prior cesarean delivery and width of the uterine cavity nor between patient age and the width of the uterine cavity in patients who were never pregnant. In the absence of other variables, the patients on oral contraceptives had smaller uterine cavities compared with those not on hormones (P=.016).
Conclusion: We have produced a standard for the measurement of the normal uterine cavity width and have shown that this width varies with gravidity and parity. The mean width of the uterine cavity of nulliparous women (27 mm) is narrower than the width of a standard intrauterine device (32 mm), suggesting that physicians should consider ultrasonography to measure the uterine cavity before inserting an intrauterine device.
Level of evidence: III.