Heterotopic Caesarean scar pregnancy combined with intrauterine pregnancy successfully treated with embryo aspiration for selective embryo reduction: case report

Ectopic pregnancy situated in a Caesarean section scar is a rare but potentially life-threatening event. Because of its rarity, there are no universal treatment guidelines to manage this condition. We report a case of IVF-induced triplet heterotopic pregnancy of early gestational age that included one Caesarean scar pregnancy diagnosed as early as 6 weeks gestation. Treatment with embryo aspiration under vaginal ultrasonography for selective embryo reduction was given and the concurrent intrauterine twin pregnancy was preserved successfully.     

Embryo reduction of multifetal pregnancies following assisted reproduction treatment: a modification of the transvaginal ultrasound-guided technique

First-trimester transvaginal embryo reduction is an effective alternative for the management of multifetal pregnancy in assisted reproduction. We have modified the transvaginal technique by performing an intracardiac embryo puncture until asystolia is verified, without the injection of any substances. Any aspiration of embryo tissues or amniotic fluid was avoided. A total of 149 multifetal pregnancies was reduced to twins (n = 134) or singletons (n = 15) at early gestational age (7.8 +/- 0.8 weeks). Eleven cases (7.3%) of miscarriage, two cases (1.3%) of chorioamnionitis, and 17 cases (11.4%) of transient spotting were recorded as postoperative complications. Vanishing of one embryo occurred in four cases (3.0%) of those reduced to twins. The baby take-home rate was 89.5% for twins and 80.0% for singletons. Pregnancy outcome was analysed and compared with a control group of women with non-reduced multiple pregnancies. The birth weight of singleton pregnancies after reduction was lower (2929 +/- 160 versus 3291 +/- 422 g; P < 0.02). These studies show that early transvaginal intracardiac embryo puncture is an effective and safe technique.     

CASE REPORT: Severe ovarian hyperstimulation syndrome, selective embryo reduction and heterotopic pregnancy

Ovarian hyperstimulation syndrome is common (21.4%) in patientswith polycystic ovarian disease, treated by gonadotrophins.It is much frequent (50%) in conceptual cycles. We report acase associated with a quadruplet pregnancy that underwent selectiveembryo reduction at 8 weeks' gestation to a twin pregnancy andwas subsequently found to have an unruptured ectopic pregnancyat 11 weeks' gestation. After laparotomy and partial salpingectomya successful twin pregnancy ensued.     

Multiple pregnancy induction and selective fetal reduction in high genetic risk couples

Couples at risk for an inherited disorder often have severalpregnancy interruptions because of affected fetuses and difficultyin achieving their desired family. We evaluated the efficiencyand acceptability of selective fetal reduction after chorionicvillus sampling (CVS) of multiple pregnancy induced by ovarianstimulation and gamete intra-Fallopian transfer (GIFT). Thisapproach has been offered to nine patients at risk of Mendeliandiseases and one patient carrier of reciprocal translocation.The acceptance has been very high (90%). One patient at riskof an autosomic recessive disease opted for artificial donorinsemination, one conceived spontaneously, and one was a poorresponder to ovarian stimulation. Seven patients actually underwenta single GIFT procedure with six achieving pregnancy (86%),all but two being a multiple pregnancy (67%). All pregnanciesconcluded uneventfully at term and newborns were alive and healthy.Prenatal diagnosis, including fetal karyotyping in all cases,was performed at 8.5–11.5 weeks of gestation and confirmedeither on amniotic fluid aspirated at reduction or at birth.The number of fetuses was reduced to one or two because thegenetic disease was present and/or to reduce the risk of prematuredelivery and improve the likelihood of successful pregnancy.The new approach seems to be highly effective and might be considereda practical and useful alternative to preimplantation geneticdiagnosis.     

Successful non-surgical management of a heterotopic abdominal pregnancy following embryo transfer with cryopreserved-thawed embryos.

Heterotopic pregnancy is an increasingly common complication of assisted reproductive technology. Abdominal pregnancy is a rare and life-threatening form of ectopic pregnancy that can present as the extrauterine portion of a heterotopic pregnancy. We present the case of a cryopreserved-thawed embryo transfer that resulted in a simultaneous intrauterine and abdominal pregnancy first recognized at 10 weeks gestation. Ultrasound-guided transvaginal injection of potassium chloride into the abdominal pregnancy resulted in asystole and spontaneous resorption of the ectopic fetus, while the intrauterine pregnancy continued and resulted in a liveborn vaginal delivery at full term. Selective embryo reduction using a non-surgical approach in a haemodynamically stable patient can therefore be considered in the management of heterotopic abdominal pregnancy if diagnosed relatively early.     

Pregnancy: First trimester embryo reduction: a medical solution to an iatrogenic problem

The incidence of multiple pregnancies is increasing, mainlyas a consequence of the widespread use of various infertilityprotocols. Since such gestations present a high risk of feto—maternalmorbidity and mortality, selective first trimester fetocideremains one of the few reasonable options. We reviewed the literaturedealing with the outcome of 804 multiple pregnancies followingthe use of transcervical, transvaginal or transabdominal approaches.Questions relating to dealing with technical failure, methodof fetocide and procedural improvements are examined. In a comparisonof the variables: miscarriage, preterm delivery, perinatal andneonatal loss rates, the transvaginal approach fares better,but statistical significance (P < 0.001) is achieved onlyfor preterm delivery. We speculated that this might be attributableto the very early gestational age at which the procedure isusually performed. However, the transabdominal approach offersbetter results when post-manipulation maternal morbidity isconsidered, i.e. infection and vaginal bleeding. Since eachoption offers different advantages and disadvantages, additionalexperience and larger population samples are required to furtherclarify this important issue.     

Avoiding multiple pregnancies in ART: multiple pregnancies: a test case for the moral quality of medically assisted reproduction

Although most professional societies have issued guidelines to diminish the number of embryos to be transferred during assisted reproduction techniques, the incidence of multiple pregnancies remains unacceptably high. The negative psychological, social and medical consequences for the patients and their offspring easily outweigh the benefits in terms of increased success rates. Multiple pregnancies would never be tolerated if the 'best interest of the child' standard was applied as strictly to these consequences, as it is to controversial family forms. The persistence of high multiple pregnancy rates is largely due to the pressure brought to bear on the physicians to increase the overall success rate. The fertility specialist should inform the patients about the risks and benefits of a multiple transfer but ultimately the specialist should decide how many embryos to transfer. Multifetal reduction is an ethically acceptable solution if, and only if, the physician has taken all reasonable steps to prevent the occurrence of a multiple pregnancy. Finally, an additional strategy to decrease the incidence of multiple pregnancies is proposed, i.e. to extend the professional responsibility of the fertility specialist to all steps of procreation including pregnancy, birth and neonatal care.     

Embryo reduction in multifetal pregnancies using saline injection: comparison between the transvaginal and the transabdominal approach.

A total of 30 patients with multifetal pregnancies, all resulting from treatment with superovulatory agents or assisted reproductive techniques, underwent embryo reduction. All patients had three or more fetuses (one sextuplet, two quintuplets, seven quadruplets and 20 triplets). The procedure was carried out using intra-embryonal injection of 0.9% sodium chloride solution. Embryo reduction was carried out via the transabdominal approach in 10 patients, performed at 11-12 weeks of gestation, and via the transvaginal route in 20 other patients, at 8-10 weeks of gestation. In the transabdominal group, one patient aborted following repeated attempts at embryo reduction while the other nine gave birth to healthy newborns (eight twins and one triplet). In the transvaginal group, four pregnancies are currently ongoing (all beyond 28 weeks of gestation), 14 pregnancies resulted in a delivery of at least one live newborn (13 twins and one singleton), one patient had a late abortion at 24 weeks' gestation and another was delivered at 27 weeks' gestation due to severe pre-eclampsia. Transvaginal ultrasound-guided needle procedures are commonly practised in most in-vitro fertilization units. The employment of this route for embryo reduction, performed at an earlier gestational age and with the use of a non-toxic substance such as 0.9% saline solution, is advocated.     

Genetics: Genetic analysis prior to selective fetal reduction in multiple pregnancy: technical aspects and clinical outcome

Multiple pregnancies resulting from ovarian stimulation areat a higher risk of carrying at least one fetus affected byMendelian or chromosomal anomalies, the incidence of which isdirectly related to the order of multiples. Genetic analysisbefore fetal reduction was offered to both high-and low-riskpregnant women carrying two or more fetuses after ovulationinduction. Chorionic villus sampling (CVS) and fetal reductionwere achieved by transabdominal needling. The use of short-termculture, the polymerase chain reaction and fresh tissue enzymaticanalyses have made it possible for genetic diagnosis to be availablein a few days. A total of 100 patients had multifetal pregnancyreduction performed by a single operator; all of them completedpregnancy and none was lost at follow-up. The total fetal lossbefore 24 weeks was 7% and no statistically significant relationshipwas found with the final number of fetuses and CVS. Perinatallosses (3.9%) were only present in the series with a final numberof two fetuses. Pregnancy duration and birthweight were significantlyhigher in singletons than in twins, but were not related toCVS. The rate of chromosomal disorders was higher (7.2%) inthe study series than in singleton pregnancies not undergoingfetal reduction. Diagnostic error due to incorrect samplingwas reported in 1.5% of cases. These data support fetal reductionas a valuable strategy to improve the outcome of multiple pregnancy.The outcome of pregnancies reduced to singletons was significantlybetter than of those reduced to twins, and was not related toCVS. Therefore, prenatal genetic diagnosis should become anintegral part of counselling on multiple pregnancy, and is stronglyrecommended when reduction to singleton pregnancy is requested.     

The cumulative embryo score: a predictive embryo scoring technique to select the optimal number of embryos to transfer in an in-vitro fertilization and embryo transfer programme.

In order to achieve a clinical pregnancy rate higher than that achieved following initial adoption of in-vitro fertilization embryo transfers, more than one embryo is transferred. This has led to a substantial increase in unwanted multiple pregnancy rates with IVF as compared with natural conception. What is therefore required is a simple, clinically useful embryo scoring system, to reflect embryo developmental potential, which will enable the selection of the optimal number of embryos to transfer in order to achieve the maximum pregnancy rate with a low incidence of high order multiple pregnancies. We believe that the Cumulative Embryo Score (CES) achieves these aims. On the day of embryo transfer the grade of each embryo transferred was multiplied by the number of blastomeres to produce a score for each embryo, and summation of the scores obtained for all the embryos transferred gave the CES. The grouped pregnancy rates obtained rose as the CES increased to maximum of 42. A continued increase in the CES above 42 did not result in any further rise in the pregnancy rate. However, an analysis of all our IVF pregnancies showed that the multiple pregnancy rate continued to rise above a CES of 42. By restricting the CES per embryo transfer to 42, 78% of triplet pregnancies and 100% of the quadruplet IVF pregnancies could have been predicted and potentially avoided.     

Survival rates during the first trimester of multiple gestations achieved by ICSI: a report of 1448 consecutive multiples

BACKGROUND: The purpose of this study was to determine the rate of spontaneous gestational sac loss during the first trimester in women achieving multiple pregnancies by ICSI. METHODS: A retrospective analysis was performed of 1448 consecutive multiple pregnancies conceived by ICSI. RESULTS: Of the cohort of 1448 pregnancies, twin gestations constituted 59.6% (864), triplets 30.2% (438) and quadruplets 10.0% (146). During the first trimester, 69 (4.7%) patients miscarried, while 179 (12.3%) continued their pregnancies and had fewer gestational sacs at the end of the first trimester than at the beginning. The overall loss rate of any gestational sac during the first trimester in these multiple pregnancies was 10.1%. There was a significant difference in the frequency of spontaneous reduction to twin or singleton pregnancies in the first trimester between women carrying triplets (11.7%) and those carrying quadruplets (3.5%) [P = 0.004; odds ratio (OR) 3.5; 95% confidence interval (CI) 1.3-9.1]. The frequency of gestational sac loss was significantly greater among women >35 years old (20.9%) than in women less than 35 years old (15.9%) (P = 0.03; OR 1.4; 95% CI 1.0-1.9). CONCLUSION: In multiple pregnancies there is a significant risk of spontaneous loss of any embryo during the first trimester. These findings should be considered prior to any decision about selective embryo reduction.     

First trimester fetal reduction: its role in the management of twin and higher order multiple pregnancies

Multiple pregnancy may be the result of stimulated or non-stimulated,and of assisted or natural conception. As observed in the pastdecade, assisted conception technologies have significantlyincreased the prevalence of multiple pregnancy. The increasehas been much more marked for triplets and higher order births.Rates of perinatal mortality and fetal and maternal complicationsare higher in twins than in singletons, and the adverse outcomerises with increasing number of multiples. Unplanned multiplepregnancy may be felt to be emotionally and physically so stressfulan experience as to drive patients to refusal of pregnancy itself,or to want to reduce the number of fetuses to an acceptablestandard. Fetal reduction techniques have emerged as a veryeffective medical approach to improve pregnancy outcome anda key option of patients trying to carry a pregnancy to term.Multiple fetuses are most frequently heterozygotes; thereforethe risk of each of them being affected by a Mendelian diseaseor sporadic chromosomal aberration is an independent probability.Thus, the incidence of genetic defects in at least one fetusis increased and directly related to the order of multiples,and this makes it worthwhile to offer karyotyping of the fetus(es)to be spared, before the reduction procedure takes place. Whena multiple pregnancy is established, one may conclude selectivereduction is the most effective therapeutic approach for reducingrisks.     

Avoiding multiple pregnancies in ART: a plea for single embryo transfer

It has been generally accepted that triplets after IVF/intracytoplasmic sperm injection (ICSI) can and should be avoided by adopting a standard strategy of replacing no more than two embryos. However, there is an increasing awareness of the risks and costs and of the epidemic size of twin pregnancies after IVF/ICSI. This has resulted in efforts to replace no more than one embryo. However, this approach has been hampered by our relative inability to identify embryos with a very high implantation potential. To identify such embryos, a number of strategies are being considered, both at the two pronuclear (2PN), early cleavage and the blastocyst stages. At the 2PN stage, the polarity characteristics of the nucleoli have been shown to be correlated with a high implantation rate. Similarly, the morphological characteristics at day 2 and 3 have been used to describe top quality embryos in approximately 75% of all IVF/ICSI cycles. Blastocyst culture has resulted in very high implantation rates in the hands of some authors. No approach has shown its superiority at present, but initial experience with single embryo transfer (SET) at the early cleavage stage by Scandinavian and Belgian groups shows that an ongoing pregnancy rate of 35% and more can be achieved. Proper identification of patients at risk of a twin pregnancy after double embryo transfer is equally important. It is clear that mainly young patients (aged <34 years) during their first, perhaps first two, IVF/ICSI cycles constitute the main population at risk (responsible for >80% of all twins) and are the main target group for twin prevention by SET of a top quality embryo at whatever stage. Therefore, in our opinion, although a further fine-tuning of both embryo and patient characteristics relating to a high risk for (twin) pregnancy is desirable, SET should be introduced carefully and progressively in each IVF/ICSI programme from now on. Correct counselling is very important and both public and private insurers will have to join in the discussion.     

Infertility: The desire for multiple births in couples with infertility problems contradicts present practice patterns

Paradoxically, the attitude of infertility patients towardsmultiple births has never been investigated. We therefore generateda survey by questionnaire, which was sent to 3800 consecutiveunselected couples with infertility problems: 582 responseswere received (15% response rate) and analysed. The percentagedistribution of the responses to 21 questions, addressing attitudestowards and knowledge about the risk of multiple gestations,was the main outcome. Worry about multiple births was expressed,independent of the number of multiples, although fear aboutmultiple conceptions was rejected by a large majority (64%).The risk of a twin birth was not strongly perceived, but theperception of risk increased with increasing numbers of multiples:triplets (50–62%), quadruplets or more (71–72%).A desire for the conception of twins was expressed by 67–90%of couples, a desire for the conception of triplets was equallyexpressed and rejected, and for a multiple gestation beyondtriplets was rejected by 73–82% of couples. Patients wereeducated about the risks of selective embryo reduction and respondedin a bimodal fashion to the option of utilizing this procedure,with equal numbers being willing to consider or reject it. Age,parity and length of infertility did not affect the couples‘worry or fear about multiples. The desire for twins and triplets,however, was correlated significantly with age (twins, P = 0.032;triplets, P = 0.03); there was no such correlation for largermultiples. The length of infertility was correlated with a positiveattitude towards multiples beyond triplets (P = 0.029) but wasnot correlated with a desire for twins or triplets. Prior paritydid not affect the attitude towards multiples at all. The lengthof infertility was also correlated significantly to an understandingof risk (twins, P = 0.034; triplets, P = 0.001; quadrupletsand more, P = 0.05), while age and parity was not. The considerationof selective embryo reduction as a treatment option was correlatedsignificantly with age (P = 0.0001), while the understandingof associated risks was evenly distributed, independent of patientcharacteristics. We conclude that infertility patients appearto be educated about the risks of multiple births. A strongdesire for multiple births, as long as this can be limited totriplets or less, increases with advancing female age. Increasinglength of infertility, however, increases the willingness formultiples beyond triplets. Increasing female age increases thereadiness to consider selective embryo reduction as a treatmentoption. Attitudes do not differ between couples with primaryand secondary infertility. Patient attitudes are thus not inagreement with the existing practice patterns in infertilitytherapy. A re-evaluation of some of these practice patternsmay therefore be indicated.     

Early embryo cleavage is a strong indicator of embryo quality in human IVF.

BACKGROUND: In order to decrease multiple birth rates without decreasing birth rates overall, it is important to increase the capability of selecting the most optimal embryos for transfer. It has been shown that human embryos which cleave early, i.e. complete the first mitotic division within 25-27 h post insemination, provide higher pregnancy and implantation rates. METHODS AND RESULTS: In this prospective study, an evaluation of 10 798 scored embryos showed that early cleavage resulted in a significantly higher proportion of good quality embryos compared with late cleavage (62.5 versus 33.4%, P < 0.0001). When examining both day 2 and day 3 transfers together, early-cleaving embryos (306 transfers) gave rise to significantly higher rates of pregnancy/transfer (40.5 versus 31.3%, P = 0.0049), implantation (28.0 versus 19.5%, P = 0.0001) and birth/ongoing pregnancy (34.3 versus 24.0%, P = 0.0009) than did late-cleaving embryos (521 transfers). A stepwise logistic regression of all data showed that the total number of good quality embryos and female age were independent predictors of both pregnancies and birth. For intracytoplasmic sperm injection (ICSI) embryos, early cleavage was found to be an independent predictor of birth. CONCLUSIONS: Early embryo cleavage is a strong biological indicator of embryo potential, and may be used as an additional embryo selection factor for ICSI embryos.     

Surgery: A successful in-vitro fertilization and embryo transfer treatment in a woman with previous vaginoplasty for congenital absence of vagina

A mock embryo transfer under ultrasound guidance helped to planan embryo transfer in a woman with previous vaginoplasty.     

The implantation of every embryo facilitates the chances of the remaining embryos to implant in an IVF programme: a mathematical model to predict pregnancy and multiple pregnancy rates

BACKGROUND: We aimed to assess the validity of a theoretical mathematical model to predict the pregnancy rate and the multiple pregnancy rate in IVF/oocyte donation programmes on the basis of the implantation rate and the number of transferred embryos. METHODS: A total of 1835 embryo transfers corresponding to three different programmes in two centres with different implantation rates were analysed. Pregnancy and multiple pregnancy rates observed in the aforementioned programmes were compared with those obtained following different mathematical models. Four models were tested: binomial model, ground model, maternal variability model and collaborative model. The goodness of fit was performed by means of the maximum likelihood fit method. RESULTS: The binomial model could not predict the pregnancy rate, and especially the multiple pregnancy rate. The multiple pregnancy rate predicted following the binomial model was much lower than observed, up to 40-fold reduced. Ground model and maternal variability model adjusted to the data with more precision, but were still not accurate. Finally, the collaborative model reproduced with very great accuracy both pregnancy rate and the multiple pregnancy rate. A collaborative parameter of 22% was found, implying that the implantation probability of each embryo is increased by 22% for every embryo previously implanted. CONCLUSIONS: Embryonic implantation does not follow a binomial law, showing that the implantation is not independent from the number of embryos implanted. The best fit to the data is obtained following a collaborative model by which the implantation of one embryo is facilitated by the implantation of other embryo(s). The mathematical formula of the collaborative model predicts very accurately the pregnancy rate and the multiple pregnancy rate in IVF/oocyte donation programmes, based on the implantation rate of this specific programme and the number of embryos transferred up to five embryos. We recommend using the aforementioned formula to quantify the pregnancy rate and the risk of multiple pregnancy in the counselling of the infertile couple at embryo transfer. Such a formula is freely available at www.ifca.unican.es/matorras/mathpreg/.     

Risks of miscarriage and early preterm birth in trichorionic triplet pregnancies with embryo reduction versus expectant management: new data and systematic review

BACKGROUND: Triplet pregnancies are associated with a high risk of miscarriage and early preterm birth. It is uncertain if the outcome is improved by embryo reduction (ER). METHODS: We examined trichorionic triplet pregnancies with three live fetuses at 10-14 weeks of gestation that were managed expectantly or by ER. The two groups were compared for the rates of miscarriage, defined as pregnancy loss before 24 weeks, and preterm delivery prior to 32 weeks. In addition, systematic searches were performed to identify studies comparing outcomes in expectant management versus ER in triplet pregnancies. RESULTS: We combined data from 365 pregnancies managed in our centre with those of five previous studies. In total there were 893 pregnancies. In the ER group (n=482) compared to the expectantly managed group (n=411), the rate of miscarriage was higher [8.1 versus 4.4%; relative risk (RR)=1.83, 95% confidence interval (CI)=1.08-3.16, P=0.036] and the rate of early preterm delivery was lower (10.4 versus 26.7%, RR=0.37, 95% CI=0.27-0.51, P<0.0001). It was calculated that seven (95% CI=5-9) reductions needed to be performed to prevent one early preterm delivery, while the number of reductions that would cause one miscarriage was 26 (95% CI=14-193). CONCLUSIONS: In trichorionic triplets, ER to twins is associated with an increase in the risk of subsequent miscarriage and decrease in risk of early preterm birth.     

In unselected patients, elective single embryo transfer prevents all multiples, but results in significantly lower pregnancy rates compared with double embryo transfer: a randomized controlled trial

BACKGROUND: Elective single embryo transfer (eSET) in a selected group of patients (i.e. young patients with at least one good quality embryo) reduces the number of multiple pregnancies in an IVF programme. However, the reduced overall multiple pregnancy rate (PR) is still unacceptably high. Therefore, a randomized controlled trial (RCT) was conducted comparing eSET and double embryo transfer (DET) in an unselected group of patients (i.e. irrespective of the woman's age or embryo quality). METHODS: Consenting unselected patients were randomized between eSET (RCT-eSET) (n = 154) or DET (RCT-DET) (n = 154). Randomization was performed just prior to the first embryo transfer, provided that at least two 2PN zygotes were available. Non-participants received our standard transfer policy [SP-eSET in a selected group of patients (n = 100), otherwise SP-DET (n = 122)]. RESULTS: The ongoing PR after RCT-eSET was significantly lower as compared with RCT-DET (21.4 versus 40.3%) and the twin PR was reduced from 21.0% after RCT-DET to 0% after RCT-eSET. The ongoing PRs after SP-eSET and SP-DET did not differ significantly (33.0 versus 30.3%), with an overall twin PR of 12.9%. CONCLUSION: To avoid twin pregnancies resulting from an IVF treatment, eSET should be applied in all patients. The consequence would be a halving of the ongoing PR as compared with applying a DET policy in all patients. The transfer of one embryo in a selected group of good prognosis patients leads to a less drastic reduction in PR but maintains a twin PR of 12.9%.     

Early cleavage of human embryos: an effective method for predicting successful IVF/ICSI outcome.

BACKGROUND: The need for effective parameters for selecting the best embryos is paramount when a large number of them are available for transfer. Other studies have reported that transfer of pre-selected embryos, based on cleavage to the 2-cell stage at 25 h and 27 h post-insemination/intracytoplasmic sperm injection (ICSI), increases implantation and pregnancy rates. We investigated whether extending the time for selection of cleaved embryos to 29 h post-insemination/ICSI had a similar effect on pregnancy and implantation rates. METHODS: Cleavage to the 2-cell stage was assessed at 25, 27 and 29 h post-insemination/ICSI. Embryos that had cleaved at any of these time points were designated as 'early cleavage' (EC), while others were designated as 'non-early cleavage' (NEC). EC embryos were selected and preferentially transferred. RESULTS: EC occurred in 57% of the cycles (61% IVF; 51% ICSI). Significantly (P = 0.02) more clinical pregnancies occurred in the EC group (23/42, 55%) compared with the group that had no embryo undergoing first cleavage up to 29 h post-insemination/ICSI (8/32, 25%). The EC group of patients was significantly younger than the NEC. CONCLUSION: Transfer of selected embryos that reached the 2-cell stage between 25 and 29 h post-insemination/ICSI is a reliable prognostic tool for patients undergoing assisted reproduction techniques.