RR (95 % CI)
N (studies)
References
Interpretation
Quality of evidence
TAUS during ETa vs. clinical touch
1.3 (1.2–1.5)
3,641 (13)
TAUS is better
High
TVUS during ET vs. TAUS during ET
1.0 (0.8–1.2)
613 (3)
No difference
Moderateb
ULM prior to ET vs. TAUS during ET
1.1 (0.9–1.2)
1,964 (3)
No difference
High
Therefore we believe that using ultrasound prior to or during ET is important for maximizing pregnancy rates. Currently, TAUS during embryo transfer is by far the most used technique; however, ULM prior to ET has two important advantages: the better patient satisfaction observer and the technique is simpler, requiring only one professional for the ET. TVUS technique is another possible technique, but it is more technically difficult [14]. However, there is no sufficient evidence for applying any other intervention either prior to or after embryo transfer, including bed rest [7, 8, 32].
See below the description of the technique from our center: we use the Cook Guardia catheter, which is a soft, curved, and echogenic catheter that has a rounded tip, which might help in avoiding trauma and improving pregnancy rates [33] (Fig. 11.1). We also use a combination between TAUS guidance during embryo transfer and ULM prior to ET.
Fig. 11.1
Two different embryo transfer catheters: Gardia (top) and Wallace (bottom)
11.2.1 Current Embryo Transfer Technique at Our Center
- 1.
We ask the women to drink water and wait until fill her bladder is comfortably full before ET.
- 2.
Just before embryo transfer starts, we perform a quick TA-US scan to assess the bladder volume and whether the uterus can be identified properly. Using a cross-sectional ultrasound scan, we can we can identify the position of the cervix in the vagina, facilitating the correct placement of the vaginal speculum (Video 11.1); a longitudinal view is better to assess whether the uterus can be correctly identified (Fig. 11.2). Regularly, the bladder volume should measure between 200–500 mL, if the bladder volume is too high, compressing the uterus, we ask the patient to partially empty her bladder; if the bladder volume is too low, impairing the uterine image, we ask the patient to drink another glass of water and wait more 30 minutes before the ET.
Fig. 11.2
Longitudinal plane of the uterus before inserting the speculum to assess bladder volume and image quality
- 3.
Still before inserting the speculum, we use the TA-US to measure the ULM. We do that by measuring the distance between the external and the internal os, and the distance between the internal os and the fundus of the endometrial cavity: ULM = the sum of these two distances. Such procedure can be performed using 2D or 3D ultrasound, and we believe that the best imaging technique and the most reliable measurements are achieved combining, 3D-US, VCI and Omniview (Figs. 11.3 and 11.4). We prefer doing that before inserting the speculum, because it is much easier to identify the external os. The measurements and the images might help the person performing the embryo transfer to properly introduce the catheter. In some cases, the distances might be much longer than usual (Fig. 11.5), and measuring them before the ET is important for planning.
Fig. 11.3
Imaging and measuring the distance between the external and internal os and between the internal os and the fundus of the uterine cavity by transabdominal ultrasound using single image (top left), multiplanar mode (top right), multiplanar combined with volume contrast imaging (VCI, bottom left), and OmniView combined with VCI (bottom right). We believe that the best imaging technique and the most reliable measurements are achieved combining 3D US, VCI, and OmniView (bottom right)
Fig. 11.4
Imaging and measuring the distance between the external and internal os and between the internal os and the fundus of the uterine cavity by transvaginal ultrasound using single image (top left), multiplanar mode (top right), multiplanar combined with volume contrast imaging (VCI, bottom left), and OmniView combined with VCI (bottom right). We believe that the best imaging technique and the most reliable measurements are achieved combining 3D US, VCI, and OmniView (bottom right)
Fig. 11.5
Imaging and measuring the distance between the external and internal os and between the internal os and the fundus of the uterine cavity by transabdominal ultrasound using OmniView and VCI. In this case the distance between the external os (≈9.5 cm) was much longer than the expected (usually ≈ 4 cm); previous planning was essential for proper embryo transfer, avoiding deploying the embryos outside the endometrial cavity. The imaging technique also permits to anticipate the curves that the catheter will need to pass before reaching the endometrial cavity
- 4.
After measuring the ULM, we subtract 2.5 cm and we place the rubber lock of the outer sheath at that distance (e.g. with a ULM = 7.5 cm the rubber lock should be placed at 5.0 cm), so we are sure that when the rubber lock reach the external os the tip of the catheter will be at 2.5 cm of the fundus of the uterine cavity.
- 5.
The person who will perform the ET should then insert the vaginal speculum and expose the cervix. It is frequently necessary to clean it with sterile gauze pads when using vaginal progesterone; however, this step is frequently unnecessary when using oral dydrogesterone for luteal phase support [34].
- 6.
The person performing the ET inserts the external sheath until the rubber lock touch the external os. This can be accompanied with the ultrasound scan to guide the insertion (Fig. 11.6, Video 11.2), orienting the best angle to position the catheter curve; we prefer reporting it as clock hours (e.g. 12h, 3h, 6h, 9h). We ask the embryologist to prepare the internal catheter with the embryo(s) only after the external sheath is properly positioned, to avoid long-time exposure of the embryo to non-ideal conditions of temperature.
Fig. 11.6
Transabdominal ultrasound showing catheter after the tip has passed the internal os. Note how the speculum impairs the proper visualization of the external os
- 7.
The person performing the embryo transfer inserts the internal catheter 1.0 cm further (until the second mark of the inner catheter reaches the internal catheter), aiming to place its tip at 1.5 cm from the fundus. At the distance, the embryos will be deposited at the mid/lower uterine cavity, avoiding placing them close to fundus, trying to maximize pregnancy rates and reduce the occurrence of ectopic pregnancies [6, 35–40]. Optionally, the person performing the TA-US measures the distance between the catheter tip and the myometrial-endometrial interface at the uterine fundus (Figs. 11.7 and 11.8) before the insertion, aiming to better calculate the distance that the inner catheter should be inserted.
Fig. 11.7
Measuring the distance between the tip of the catheter and the myometrial-endometrial interface at the uterine fundus using 2D transabdominal ultrasound
Fig. 11.8
Measuring the distance between the tip of the catheter and the myometrial-endometrial interface at the uterine fundus using 3D transabdominal ultrasound in the same case but now combining OmniView and VCI. We believe this imaging provides more reliable measurements and also permit the people performing the embryo transfer to better plan whether the curve of the external catheter should be pointed before inserting the internal catheter with the embryos
- 8.
The plunger should be gently pressured, aiming to slowly insert the embryos, media and air bubles inside the uterine cavity [41–43] (Video 11.3). The pressure on the plunger must be sustained, and the operator should gently and simultaneously remove both catheters to avoid applying a negative pressure and “aspirating” the embryos [6].
- 9.
- 10.
After the embryo transfer, the catheter should be immediately assessed by an embryologist. In the eventuality of a retained embryo, the ET should be repeated.
- 11.
11.3 Important Technical Tips
A good image quality is important for proper measurement: adjust gain, depth, focus, and magnification and try using harmonics imaging, particularly when the bladder volume is high. Additionally, the measurement should be performed just before the ET, as a different bladder volume/pressure can interfere with the uterine measurements, i.e., a large bladder volume applies pressure on the uterus, reducing its height but increasing its length and width.
The measurement might be performed by TVUS with an empty bladder or by TAUS with a comfortably full bladder. Using TVUS with an empty bladder is probably more comfortable for the patient but might result in more difficult ETs, as a full bladder possibly straightens the utero-cervical angle. However, there is not sufficient evidence to support the use of a full bladder to improve pregnancy rates [14].
Avoid changing the catheter frequently; the personal experience with a catheter might be relevant for the success, and the results during the learn curve might be suboptimal [13, 47–49].
Difficult ET or pain during the procedure is associated with reduced pregnancy rates [1, 50]. Although there is no universally accepted method to deal with this situation [51], a mock embryo transfer prior to IVF cycle might predict this event [52]. In our center, we perform endometrial injury using a Pipelle during the menses just before the ovarian stimulation or endometrial preparation for IVF. Besides the possibility of planning the embryo transfer, this procedure could also improve pregnancy rate [53–55]. When a difficult ET is predicted by a difficult insertion of a Pipelle and uterine sound, we offer to perform a cervical dilatation under analgesia; this procedure might reduce the risk of a difficult ET leading to an easier ET and higher pregnancy rates [56].
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