Editing Embryo transfer (section)

== Embryo number ==
A major issue is how many embryos should be transferred, since placement of multiple embryos carries a risk of multiple pregnancy. While the past physicians placed multiple embryos to increase the chance of pregnancy, this approach has fallen out of favor. Professional societies, and legislatures in many countries, have issued guidelines or laws to curtail the practice.<ref>{{cite web|url=http://www.newlife-ivf.co.uk/blog/ivf-laws-in-greece-2014.php |title=New Law regarding the number of embryos transferred in Greece |publisher=newlife-ivf.co.uk |date=22 December 2014}}</ref> There is low to moderate evidence that making a double embryo transfer during one cycle achieves a higher live birth rate than a single embryo transfer; but making two single embryo transfers in two cycles has the same live birth rate and would avoid multiple pregnancies.<ref>{{Cite journal|title=Number of embryos for transfer following in vitro fertilisation or intra-cytoplasmic sperm injection|vauthors=Kamath MS, Mascarenhas M, Kirubakaran R, Bhattacharya S|journal=Cochrane Database of Systematic Reviews|year=2020|volume=2020|issue=8 |pages=CD003416|publisher=Cochrane Database Syst Rev.|publication-date=21 August 2020|doi=10.1002/14651858.CD003416.pub5|pmid=32827168|pmc=8094586}}</ref>

The appropriate number of embryos to be transferred depends on the age of the woman, whether it is the first, second or third full IVF cycle attempt and whether there are top-quality embryos available. According to a guideline from The [[National Institute for Health and Care Excellence]] (NICE) in 2013, the number of embryos transferred in a cycle should be chosen as in following table:<ref name="nice2013">[http://guidance.nice.org.uk/CG156 Fertility: assessment and treatment for people with fertility problems]. [[NICE guidelines|NICE clinical guideline]] CG156 – Issued: February 2013</ref>

{|class="wikitable"
! Age !! Attempt No. !! Embryos transferred
|-
|rowspan=3| <37 years || 1st || 1
|-
| 2nd || 1 if top-quality
|-
| 3rd || No more than 2
|-
|rowspan=3| 37–39 years ||rowspan=2| 1st & 2nd || 1 if top-quality
|-
| 2 if no top-quality
|-
| 3rd || No more than 2
|-
| 40–42 years ||  || 2
|}

=== e-SET<!--'Elective-single embryo transfer', 'Elective-Single Embryo Transfer', 'E-SET' redirect here--> ===
{{Redirect|e-SET|the mathematical concept|E-set}}
The technique of selecting only one embryo to transfer to the woman is called '''elective-single embryo transfer'''<!--boldface per WP:R#PLA--> ('''e-SET'''<!--boldface per WP:R#PLA-->) or, when embryos are at the blastocyst stage, it can also be called ''elective single blastocyst transfer (eSBT)''.<ref name=mullin>{{cite journal | vauthors = Mullin CM, Fino ME, Talebian S, Krey LC, Licciardi F, Grifo JA | title = Comparison of pregnancy outcomes in elective single blastocyst transfer versus double blastocyst transfer stratified by age | journal = Fertility and Sterility | volume = 93 | issue = 6 | pages = 1837–43 | date = April 2010 | pmid = 19249756 | doi = 10.1016/j.fertnstert.2008.12.137 | doi-access = free }}</ref> It significantly lowers the risk of multiple pregnancies, compared with e.g. Double Embryo Transfer (DET) or ''double blastocyst transfer'' (2BT), with a twinning rate of approximately 3.5% in sET compared with approximately 38% in DET,<ref name=Fauque>{{cite journal | vauthors = Fauque P, Jouannet P, Davy C, Guibert J, Viallon V, Epelboin S, Kunstmann JM, Patrat C | title = Cumulative results including obstetrical and neonatal outcome of fresh and frozen-thawed cycles in elective single versus double fresh embryo transfers | journal = Fertility and Sterility | volume = 94 | issue = 3 | pages = 927–35 | date = August 2010 | pmid = 19446806 | doi = 10.1016/j.fertnstert.2009.03.105 }}</ref> or 2% in eSBT compared with approximately 25% in 2BT.<ref name=mullin /> At the same time, [[pregnancy rate]]s is not significantly less with eSBT than with 2BT.<ref name=mullin /> That is, the cumulative live birth rate associated with single fresh embryo transfer followed by a single frozen and thawed embryo transfer is comparable with that after one cycle of double fresh embryo transfer.<ref name="auto" /> Furthermore, SET has better outcomes in terms of mean gestational age at delivery, mode of delivery, birthweight, and risk of [[neonatal intensive care unit]] necessity than DET.<ref name=Fauque /> e-SET of embryos at the cleavage stage reduces the likelihood of live birth by 38% and multiple birth by 94%.<ref name=gelbaya>{{cite journal | vauthors = Gelbaya TA, Tsoumpou I, Nardo LG | title = The likelihood of live birth and multiple birth after single versus double embryo transfer at the cleavage stage: a systematic review and meta-analysis | journal = Fertility and Sterility | volume = 94 | issue = 3 | pages = 936–45 | date = August 2010 | pmid = 19446809 | doi = 10.1016/j.fertnstert.2009.04.003 }}</ref> Evidence from randomized, controlled trials suggests that increasing the number of e-SET attempts (fresh and/or frozen) results in a cumulative live birth rate similar to that of DET.<ref name=gelbaya />

The usage of single embryo transfer is highest in Sweden (69.4%), but as low as 2.8% in the USA. Access to public funding for ART, availability of good [[cryopreservation]] facilities, effective education about the risks of multiple pregnancy, and legislation appear to be the most important factors for regional usage of single embryo transfer.<ref name=Maheshwari2011>{{cite journal | vauthors = Maheshwari A, Griffiths S, Bhattacharya S | title = Global variations in the uptake of single embryo transfer | journal = Human Reproduction Update | volume = 17 | issue = 1 | pages = 107–20 | year = 2010 | pmid = 20634207 | doi = 10.1093/humupd/dmq028 | doi-access = free }}</ref> Also, personal choice plays a significant role as many subfertile couples have a strong preference for twins.<ref name=Maheshwari2011 />