History of aspiration pressure
Dana B. McQueen, M.D., M.A.S., Christina Boots, M.D., Tarun Jain, M.D., John Zhang, Ph.D., and Jared C. Robins, M.D.
Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology
Northwestern University Feinberg School of Medicine, Chicago, Illinois
The aspiration pressure utilized for oocyte retrieval is provider and clinic dependent and guided by studies performed during the early development of in vitro fertlization (IVF). Little data exists regarding the impact of aspiration pressure on oocyte yield, embryo quality and pregnancy outcomes in the modern era.
As the techniques used to retrieve oocytes for IVF have evolved, the ideal aspiration pressure has been questioned. In 1974, Lopata et al. (1) compared the collection of oocytes using 120-180 mmHg (low pressure) to 200 mmHg (high pressure) and found that there were a higher number of oocytes aspirated using high pressures (1.1 vs. 2.8). In contrast, Edwards et al. (2) in 1980 described the laparoscopic collection of oocytes using a vacuum suction of no more than 120mmHg “in order to avoid damage to the oocyte”, but gave no evidence that higher pressures resulted in increased damage (2). Reports of the first percutaneous oocyte aspiration used pressures of 100 to 170 mmHg and found no oocytes with signs of mechanical damage; concluding that this was the appropriate pressure range for oocyte retrieval (3). Cohen et al. (4) in 1986 showed significantly less oocytes with mechanical damage when a mechanical pump using a suction of 120 mmHg was used compared to a manual syringe, 1% versus 16% (P <.001). The authors ended their manuscript stating, “it is unknown what the optimal pump suction pressure is when continuous pump suction is used and the present results indicate that more investigations are needed” (4). Despite this, there has been relatively little published further on the optimal aspiration pressure for oocyte retrieval.
Currently, many providers express concern if pump pressures are just a few mmHg over their standard settings of 100 to 110 mmHg. In our practice however, several providers routinely use pump pressures of > 300 mmHg. This gave us an opportunity to investigate the impact of drastic changes in aspiration pressure on oocyte yield, embryo quality and pregnancy outcomes.
This study was evaluated and approved by the Northwestern University Institutional Review Board. We retrospectively reviewed all oocyte retrievals between September 1, 2016 and August 31, 2017 to compare low-pressure oocyte aspiration (less than 150 mmHg) versus high-pressure oocyte aspiration (>300 mmHg). Oocyte aspiration was performed using a 17-gauge Wallace needle, 33 cm tubing, and a Rocket CraftTM DUO-VAC Suction Pump (Rocket Medical) 240V/50Hz. There were two physicians in the low aspiration pressure group, and five physicians in the high-pressure group.
One hundred seventy-one oocyte retrievals using low pressure and 366 retrievals using high pressure were included. There were no significant differences in mean age, body mass index, antimüllerian hormone level, number of days of stimulation, or mean total gonadotropin dose between groups (Table 1). Prior to retrieval, there was no significant difference in the number of follicles measured, 15.0 (standard deviation 9.0) in the low-pressure group and 14.5 (standard deviation 8.3; P =.53) in the high-pressure group. In the low-pressure group, there were significantly more oocytes retrieved (16 vs. 13, P <.001), greater oocyte maturity (77.4% vs 75.0%, P<.02), and fewer oocytes with an empty zona pellucida (2.0% vs 3.4%, P<.001) compared to the high-pressure group. There was no difference in the fertilization rate between groups (72.9% vs. 73.0%, P=.99) (Table 2).
There were 232 cycles cultured to the blastocyst stage. Of these, the blastocyst rate per fertilized oocyte was not significantly different (45% vs. 48%, P=.2). Among fresh embryo transfers, the pregnancy rate was not significantly different (53.8% vs. 54.9%, P=1.0). However, the low-pressure group had significantly more usable embryos, defined as the number of embryos either transferred or frozen (4.5 vs. 3.8, P=.01) (Table 2).
While use of low aspiration pressure resulted in significantly less oocytes with an empty zona pellucida, this difference was not as dramatic as anticipated using pressures > 300mmHg. In addition, the pregnancy rate was no different between groups. Interestingly, there was a greater yield of mature oocytes using low aspiration pressure and, as a result, a higher number of usable embryos in the low-pressure group.
We hypothesize, that with high aspiration pressure, follicles can collapse prior to oocyte entry into the aspiration needle and result in a lower oocyte yield. In addition, there is a rapid acceleration of the oocyte cumulus complex at the time of follicular puncture. This acceleration may result in stripping of the cumulus cells from the oocyte. Once within the needle, the velocity of follicular fluid can cause a shear stress on the cumulus oocyte complex. At low pressure, the flow within the aspiration needle remains laminar. However, the fluid flow within a 16-gauge the needle will change from laminar to turbulent when vacuum is increased to 375 mmHg (5). This turbulent flow may result in the increased number of oocytes with empty zona pellucida in the high-pressure group.
In our practice, the aspiration pressure utilized during oocyte retrieval has been traditionally set by provider preference. These preferences were influenced by individual provider experience, training, and the speed at which oocyte retrievals can be performed. We do not anticipate that these results would differ in fresh or frozen cycles. However, given the higher number of usable embryos in the low-pressure group, we anticipate that the cumulative pregnancy rate would be higher over time.
Our data suggests that using a low aspiration pressure during oocyte retrieval is preferable, as it results in a higher yield of mature oocytes and higher number of usable embryos compared to high aspiration pressures. It should be reassuring, however, that even at aspirations pressures >300 mmHg, pregnancy rates are equivalent.
1. Lopata A, Johnston IW, Leeton JF, Muchnicki D, Talbot J, Wood C. Collection of human oocytes at laparoscopy and laparotomy. Fertil steril 1974;25:1030-8
2. Edwards RG, Steptoe PC, Purdy JM. Establishing full term human pregnancies using cleaving embryos grown in vitro. Br J Obstet Gynaecol. 1980;87(9):737-56
3. Lenz S, Lauritsen JK. Ultrasonically guided percutaneous aspiration of human follicles under local anesthesia: A new method or collecting oocytes for invitro fertilization. Fertil Steril. 1982;38:673-7
4. Cohen J, Avery S, Campbell S, Mason B, Riddle A, Sharma V. Follicular aspiration using a syringe suction system may damage zona pellucida. J In Vitro Fert Embryo Transfer 1986;4:224-226.
5. Horne R, Bishop C, Reeves G, Wood C, Kovacs G. Aspiration of oocytes for in-vitro fertilization. Human Reprod Update 1996;2(1):77-85.