Assessment of pregnancy-associated, within-woman change in uterine length

To evaluate how absolute uterine length changes as a result of pregnancy.

Longitudinal repeated-measures study of all women presenting to a university-affiliated clinic for uterine sounding prior to in vitro fertilization (IVF) who went on to deliver at term and return for repeat measurement from 2002 to 2012. Change in uterine length was assessed by the Wilcoxon signed-rank test.

Among 495 women, mean pregnancy-associated change in uterine length was 0.0 cm (SD ± 0.7, p = 0.84), with 31% of women experiencing no change and 75% of women experiencing a change ≤0.5 cm. Mean uterine lengths at pre-cycle and repeat measurement were 7.2 cm (SD ± 0.7) and 7.2 cm (SD ± 0.7) with medians of 7.0 cm (IQR 7.0-7.5) and 7.0 cm (IQR 6.8-7.8), respectively. Change in uterine length did not vary by gestational number or within time interval between measurements (all p > 0.5).

There was no difference in uterine length before and after term pregnancy. The finding of minimal variation in uterine length both across and within women suggests uterine length may be relatively stable such that patients undergoing IVF after term IVF pregnancy may not require repeat measurement. Future studies might assess pregnancy-associated sonographic changes in uterine volume and the relationship between uterine length and IVF outcomes.