Objective: To assess regional changes in ultrasound-derived indices of blood flow in the dominant human follicle after the plasma LH surge.
Design: A cross-sectional, prospective study.
Setting: Reproductive medicine unit at a university.
Patient(s): Women attending an assisted conception clinic to determine the appropriate time to transfer previously frozen embryos during a natural cycle.
Intervention(s): Transvaginal ultrasonography with color Doppler imaging and pulsed Doppler spectral analysis was used to obtain indices of blood flow and velocity from vessels in the base, lateral part, and apex of the dominant follicle on days 10-12 (from day 1 of menses) and after the LH surge, but before rupture. Immunoassays were used to measure the blood concentrations of LH twice daily (at 8-10 A.M. and 4-6 P.M.) from cycle day 10.
Main outcome measure(s): The pulsatility index (PI), resistance index (RI), peak systolic velocity (PSV), and time-averaged maximum velocity (TAMXV) in the uterine arteries and three regions of the dominant follicle (apical, lateral, and basal parts); follicular volume; the day and time of the onset of the LH surge (defined as first concentration of LH > 22 U/L) and the times of each scan.
Result(s): Twenty-two women (aged 28-39 years) were studied and seven were scanned on days 10-12. A retrospective examination of the data from the remainder showed that eight were scanned < 20 hours after onset of the LH surge and seven were scanned > 20 hours after the onset of the LH surge. There was a significant increase in follicular volume after the LH surge. The PI was similar in vessels from the base (0.86 +/- 0.11; mean +/- SEM), lateral part (0.72 +/- 0.51) and apex (0.67 +/- 0.09) at cycle days 10-12 and then gradually decreased in the apex. There were similar changes in the RI. The PSV (mean +/- SEM; cm/s) was similar in vessels from the base (10.1 +/- 1.64), lateral side (8.2 +/- 1.43), and apex (9.2 +/- 1.91) in follicles of days 10-12. Within 20 hours of the onset of the LH surge, the PSV had increased in basal vessels (23.4 +/- 4.10), remained similar in lateral vessels (11.64 +/- 3.18), and was undetectable in apex vessels from six of eight follicles. Twenty hours after the LH surge, there was no pulsatile blood flow observed in the apical part of the follicle, but there was a sustained high PSV in the base (15.73 +/- 3.42) and lateral side (9.02 +/- 1.5). There were corresponding changes in the TAMXV.
Conclusion(s): During the ovulatory process there are prominent changes in the regional blood flow of the follicle with a marked increase of the flow to the base of the follicle and a concomitant decrease of blood flow to the apex. These changes may be essential for the release of a mature oocyte.