Transvaginal oocyte retrieval during assisted reproductive technologies (ARTs) was first introduced in 1981, replacing both surgical egg collection and laparoscopic retrieval but also previous different approaches such as the transurethral ultrasound-guided route. It is well known that the number of oocytes retrieved depends on many factors: type of aspiration needle (wide or narrow bore or single or double channel), aspiration pressure, follicular flushing, timing of HCG triggering, and experience and skills of the surgeon.

In IVM critical factors are the aspiration pressure and the gynecological skills because the target is the collection of oocytes from sometimes primed but not properly stimulated ovaries with smaller follicular size; the follicle’s volume varies by the cube of its radius: for instance, a 5 mm and a 10 mm follicle contain 1/8th and 1/64th the volume of a 20 mm diameter follicle, respectively (Table 12.1).

Table 12.1

Follicle diameter and fluid volume

Follicle diameter (mm)	Fluid volume (mL)	Hemisphere surface area (mm²)
4	0.034	25
6	0.113	56
8	0.263	101
10	0.524	157
12	0.955	226
14	1.437	306
20	4.189	625

Thus antral follicles of 3 mm may contain a competent oocyte, but will have approximately 1/300th the amount of fluid of a normal dominant follicle, with practical consequences on the oocyte aspiration technique [1].

Trounson et al. suggested that compared to conventional IVF in IVM, there are many factors that affect quality and number of retrieved oocytes:

Needle length
Bevel of the needle
Rigidity of the needle
Aspiration pressure

Critical aspects to deal with are also the higher risk of bleeding and pain for the patient during and after the collection of immature eggs.

Conventional IVF oocyte retrieval is a bloody operation in which a patient’s blood loss is not easily visualized; Dessole et al. analyzed the reduction of plasmatic hemoglobin on a sample of 220 IVF patients estimating an average blood loss of about 230 mL after 24 h of uncomplicated oocyte retrieval procedure [2]. Limiting blood loss may be especially important in IVM (Fig. 12.1) cases since PCO patients are at greater risk for ovarian hemorrhage after conventional IVF retrievals; a retrospective analysis performed by Liberty et al. in PCO patients showed higher risk of bleeding compared to all other patients (odds ratio 50, 95% confidence interval 11–250) [3].

../images/462633_1_En_12_Chapter/462633_1_En_12_Fig1_HTML.png — Fig. 12.1

Limiting blood loss may be especially important in IVM cases since PCO patients are at greater risk for ovarian hemorrhage after conventional IVF retrievals

12.1 Needle

Different parameters are to be taken in account looking at the characteristics of an optimal IVM needle:

Gauge
Bevel length
Angle
Tip
Stiffness
Dead space

The needle gauge could affect the outcome of the oocyte collection in terms of number of retrieved eggs, tissue trauma, and consequent bleeding (Fig. 12.2). Early studies reported that higher number of oocyte recovery corresponded to larger gauge needles used, but afterwards Awonuga et al. compared transvaginal oocyte retrievals with 15-, 17-, or 18-gauge needles founding similar results for number of collected oocytes, but less pain with smaller size needles [4].

../images/462633_1_En_12_Chapter/462633_1_En_12_Fig2_HTML.png — Fig. 12.2

Internal and external dimensions of the needles in relation to the gauge

Seyhan et al. analyzed pain scores with different gauge needles comparing a 19-gauge needle for IVM with a 16- or 17-gauge IVF needle: they found a trend of lower pain scores with 19-gauge needle, although not statistically significant; they suggested that smaller needles could give a more comfortable collection, even if in IVF enlarged ovaries with multiple large follicles and higher aspiration pressure could cause more pain. It is likely that within the range of conventional needles, smaller size results in less pain intra- and postoperatively, with a similar number of collected oocytes [5].

This may be particularly important in ART settings in which limited anesthesia is available for the patient. Seyhan et al. compared IVM patients in cases using a 19-gauge needle to IVF patients in cases using a 16- or 17-gauge needle. Records on 375 patients were reviewed retrospectively.

There were several approaches to anesthesia, but 233 patients received conscious sedation with midazolam and fentanyl together with a paracervical block.

12.2 Gauge

Patients ranked the amount of pain they experienced during the procedure on a scale of 1 to 10. There was no difference in the pain experience of the groups. Note that in addition to different gauge needles, this study compared different aspiration procedures since IVF required passage of the needle through the vagina and into each ovary only once, whereas IVM required a number of punctures in each ovary.

The authors viewed the results as showing that a smaller gauge needle was less traumatic since multiple insertions of the 19-gauge needle caused no more pain than two insertions of the larger needle. Several studies from the IVF literature also suggest that smaller needles cause less pain for women who are lightly sedated during retrieval; however, more studies are needed to confirm this.

Given the same needle bevel length (Fig. 12.3) (measured along the outer horizontal barrel edge), a smaller gauge needle will form a smaller angle and thus be sharper, passing easily through tissue; experimental data on tissue–needle interaction found that when a beveled needle has a smaller angle, there is less tissue deformation before the needle pierces that structure and less deformation of the follicle during entry, making placement of the end of the needle in the middle of the follicle easier [6].

../images/462633_1_En_12_Chapter/462633_1_En_12_Fig3_HTML.jpg — Fig. 12.3

The angle bevel and length of bevel

The bevel length for many conventional IVF needles is about 3 mm (Table 12.2); the surface area of the scoring on the bevel is 50% of a segment of the needle barrel of that length, but can only be seen in the orientation where the back of the needle faces the probe.

Table 12.2

Needle characteristics

Manufacturer (identification number)	Gauge	Lumen	Needle length (cm)	Bevel length (mm)	Bevel angle (degrees)^a	Needle dead space (mL)^a	Total dead space (mL)	Length ultrasound scoring (mm)	Ultrasound scoring begins	Diamond tip?	Flow rate (mL/s)^b
Cooper-Smith, Trumbull, CT(AR-N1695)	16	Single	35	5	18.3	0.392	1.57	22	Tip	Angled bevel	0.78
Cook Medical, Spencer, IN (K-OPSD-1635-A-S-US)	16	Double	41	5	18.3	0.291^c	1.31	5	1 mm above bevel top	No	0.45
Smiths. Medical, Kent, UK (Wallace, 0NS1733LL-500)	17	Single	36	3	26.2	0.322	0.93	23	Tip	Yes	0.42
Smiths Medical, Kent, UK (Wallace, ONS18333LL-500)	18	Single	36	3	22.9	0.199	0.74	23	Tip	Yes	0.31
Cook Medical, Spencer, IN (K-OPS-7035-RWH-ET)	15	Single	41	3	19.6	0.152	0.58	5	2 mm above bevel top	Yes	0.21
IVFETFLEX.com, Ganz, Austria (Steiner-Tan 21 gauge)	21	Pseudo-double	8	3	15.3	0.017	0.012^d	9	0.5 mm above bevel top	Yes	0.30

^aUsing data from [7] and length measurement

^bUsing a craft suition unit aspiration pump with pressure set at 1 CO mmHg

^cMeasured

^dTubing and larger sheathed needle were not counted as dead space since they can be flushed

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Tags: Pick Up and Oocyte Management

Mar 28, 2021 | Posted by admin in OBSTETRICS | Comments Off

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