Obstetric outcome of twin pregnancies after in-vitro fertilization: a matched control study in four Dutch university hospitals

In singleton pregnancies after in-vitro fertilization (IVF), increased rates of obstetric and perinatal complications have been reported. Studies that compared IVF twin pregnancies with spontaneously conceived twins have yielded conflicting results. We compared 96 IVF twin pregnancies to 96 controls after elaborate matching. The design of our study precluded matching by zygosity. The monozygosity rate was higher in the control group and this implies that beforehand the risk for a less favourable outcome in the control group was higher than in the IVF group. However, the average birthweight of the IVF children was less than that of children in the control group (P = 0.04). This was not due to more intrauterine growth retardation in the IVF group. The mean gestational age at birth was 5 days shorter in IVF than control pregnancies, and although this difference was not significant it might explain the lower birthweight in the IVF group. The discordance rate in the IVF group was significantly increased. We found no difference in perinatal mortality and morbidity. We conclude that this study provides further evidence for a different outcome of IVF twin pregnancies in comparison with spontaneously conceived twin pregnancies.     

Obstetric outcome among women with unexplained infertility after IVF: a matched case-control study

BACKGROUND: Infertility itself and also assisted reproductive treatment increase the incidence of some obstetric complications. Women with unexplained infertility are reported to be at an increased risk of intrauterine growth restriction during pregnancy, but not for other perinatal complications. METHODS: A matched case-control study was performed on care during pregnancy and delivery, obstetric complications and infant perinatal outcomes of 107 women with unexplained infertility, with 118 clinical pregnancies after IVF or ICSI treatment. These resulted in 90 deliveries; of these, 69 were singleton, 20 twin and one triplet. Two control groups were chosen from the Finnish Medical Birth Register, one group for spontaneous pregnancies (including 445 women and 545 children), matched according to maternal age, parity, year of birth, mother's residence and number of children at birth, and the other group for all pregnancies after IVF, ICSI or frozen embryo transfer treatment (FET) during the study period (including 2377 women and 2853 children). RESULTS: Among singletons, no difference was found in the mean birthweight, and the incidence of low birthweight (<2500 g) was comparable with that of the control groups. No differences were found in gestational duration, major congenital malformations or perinatal mortality among the groups studied. Among singletons in the study group, there were more term breech presentations (10.1%) compared with both spontaneously conceiving women and all IVF women (P < 0.01). The rate of pregnancy-induced hypertension was significantly lower among singletons in the study group (P < 0.05) compared with other IVF singletons. The multiple pregnancy rate was 23.3% in the study group. The obstetric outcome of the IVF twins was similar to both control groups. CONCLUSIONS: The overall obstetric outcome among couples with unexplained infertility treated with IVF was good, with similar outcome compared with spontaneous pregnancies and IVF pregnancies generally.     

Perinatal outcome of 12,021 singleton and 3108 twin births after non-IVF-assisted reproduction: a cohort study

Perinatal outcome of pregnancies caused by assisted reproduction technique (ART) is substantially worse when compared with pregnancies following natural conception. We investigated the possible risks of non-IVF ART on perinatal health. We conducted a retrospective cohort study with two exposure groups: a study group of pregnancies after controlled ovarian stimulation (COS), with or without artificial insemination (AI), and a naturally conceived comparison group. We used the data from the regional registry of all hospital deliveries in the Dutch-speaking part of Belgium during the period from January 1993 until December 2003 to investigate differences in perinatal outcome of singleton and twin pregnancies. 12 021 singleton and 3108 twin births could be selected. Naturally conceived subjects were matched for maternal age, parity, fetal sex and year of birth. The main outcome measures were duration of pregnancy, birth weight, perinatal morbidity and perinatal mortality. Our overall results showed a significantly higher incidence of prematurity (<32 and <37 weeks), low and very low birth weight, transfer to the neonatal intensive care unit and most neonatal morbidity parameters for COS/AI singletons. Twin pregnancies resulting from COS/AI showed an increased rate of neonatal mortality, assisted ventilation and respiratory distress syndrome. After excluding same-sex twin sets, COS/AI twin pregnancies were at increased risk for extreme prematurity and very low birth weight. In conclusion, COS/AI singleton and twin pregnancies are significantly disadvantaged compared to naturally conceived children.     

Pregnancy: The increased risk of complication observed in singleton pregnancies resulting from in-vitro fertilization (IVF) does not seem to be related to the IVF method itself

Singleton pregnancies resulting from in-vitro fertilization(IVF) seem to have an increased risk of obstetric and paediatriccomplications. In a retrospective study we compared, duringthe same period, 162 IVF singleton pregnancies with 263 pregnanciesresulting from stimulated cycles (without IVF) and with 5096natural pregnancies. No significant difference was found betweenthe first two groups concerning complications (i.e. prematurity,low birthweight, small-for-gestational-age and perinatal mortality).The results indicate that an adverse outcome is more commonfor pregnancies after ovarian stimulation (with or without IVF)compared to natural pregnancies. Therefore the increased riskdoes not appear to be linked to the IVF method itself but ratherto a common factor in these two populations, i.e. populationcharacteristics, underlying infertile status and/or ovarianstimulation.     

Obstetric and perinatal outcome of pregnancies after intrauterine insemination.

The main aim of this study was to evaluate the obstetric and perinatal outcome of pregnancies after intrauterine insemination (IUI) with the partner's spermatozoa combined with ovarian stimulation. Information concerning the antenatal care and obstetric and perinatal outcome of IUI pregnancies (n = 111), spontaneous (n = 333) and in-vitro fertilization (IVF) (n = 333) was obtained from the Finnish Medical Birth Register (MBR). The multiple birth rate in the IUI group was 17% (19/111). Significantly less antenatal care was required by the IUI group than the IVF group. The frequency of Caesarean section was 25% for IUI singletons and 58% for IUI multiples, similar to the other groups. The mean (SD) gestational age for IUI singletons at birth was 39.5 (1.8) weeks, with a mean birth weight of 3285 (575) g, compared with 3448 (600) g in non-assisted singletons (P < 0.05). For IUI multiples the mean gestational age at birth was 36.0 (2.8) weeks and the mean birth weight was 2449 (678) g. The incidence of preterm birth, low birth weight or low Apgar scores and the need for neonatal care were similar in all groups. One case of major malformation and two perinatal deaths were recorded in the IUI group. In conclusion, IUI treatment did not appear to increase obstetric or perinatal risks compared with matched spontaneous or IVF pregnancies. Most problems were associated with patient characteristics and multiple pregnancy. Reduction of the high incidence of multiple pregnancies after assisted reproductive technology is essential to improve its outcome.     

Comparison of outcome of pregnancy after intra-uterine insemination (IUI) and IVF

INTRODUCTION: Pregnancy outcome after IVF has been shown to be worse than after spontaneous conception. There is discussion as to whether this results from the technique itself or the patient characteristics. This study compares pregnancy outcome after IVF and intra-uterine inemination (IUI) in a matched patient group. METHODS: Data were obtained from our IVF and IUI databases (1997-2001). Matching was performed for maternal age, parity and plurality, and 126 IUI pregnancies were compared with 126 IVF pregnancies. Outcome variables were pregnancy duration, birth weight, Caesarean section rates, preterm contraction rates, neonatal intensive care unit admission, Apgar score, blood loss rates and maternal hypertension. RESULTS: None of the analysed parameters was statistically different between the groups. CONCLUSION: This matched case-control study does not show different pregnancy outcomes after IVF and IUI. Since there is no reason to believe that the IUI technique in itself leads to an increased obstetric or neonatal risk, this study suggests that the worse pregnancy outcome after IVF as compared with spontaneous conceptions is due to the specific patient characteristics, rather than to the use of IVF itself.     

Risk of spontaneous abortion in singleton and twin pregnancies after IVF/ICSI

BACKGROUND: The risk of spontaneous first trimester abortion is estimated to be between 10 and 20%. Although it is common knowledge that the incidence of abortion decreases as pregnancy progresses, exact data in relation to the duration of pregnancy are scarce. METHODS: We reviewed 1597 clinical IVF/ICSI pregnancies with known outcome and tabulated the number of miscarriages or fetal demise per intervals of 2 weeks. We furthermore compared the outcome in terms of fetal survival of 1200 singleton pregnancies with that of 397 twin pregnancies. RESULTS: The overall incidence of non-ongoing singleton pregnancies was 21.7%. Fetal death, after positive heart activity had been recorded, occurred in 12.2% of singleton pregnancies. The overall incidence of spontaneous abortion in twin pregnancies was 17.1% (12.1% vanishing twins and 5.0% complete miscarriages). The incidence of miscarriage in the twin pregnancies, expressed per gestational sac, was 11.1%. Once fetal heart activity was present, the risk of abortion (per gestational sac) was 7.3%, which is significantly lower than that in singleton pregnancies. CONCLUSIONS: Our data give an estimate of the probability of miscarriage or fetal demise at any given period of the first trimester both for singleton and twin pregnancies. Twin pregnancies after IVF have a better potential for survival than singleton pregnancies.     

The effect on IVF outcome of small intramural fibroids not compressing the uterine cavity as determined by a prospective matched control study

BACKGROUND: Several studies have reported that the presence of intramural fibroids affects conception following IVF. We attempted to corroborate or refute the conclusions relating to IVF and leiomyomas of the aforementioned studies. METHODS: Women with small intramural leiomyomata (< or = 5 cm) discovered on initial pelvic sonographic studies performed in preparation for IVF were prospectively matched by age, with the next patient of the same age undergoing IVF who did not demonstrate fibroids (controls). RESULTS: Though no significant differences were found in outcome when comparing these two groups, there was a distinct trend for lower live delivery rates and higher miscarriage rates. CONCLUSIONS: These data support the conclusions of the only other prospective matched control study evaluating similar factors, i.e. that small intramural fibroids can negatively affect IVF outcome. Nevertheless, we think that a multicentre study should be conducted first before evaluating whether myomectomy improves outcome or not.     

Defining the rise of serum HCG in viable pregnancies achieved through use of IVF

BACKGROUND: We aimed to characterize the rate of HCG rise associated with viable IVF pregnancies, and to evaluate the association between HCG rise and potentially influential factors. METHODS: We performed a retrospective cohort analysis of all viable pregnancies achieved through IVF at two centres between January 1999 and March 2004. RESULTS: Of the 455 pregnancies resulting in live births, 391 met inclusion criteria and contributed a total of 1052 HCG values. Using random effects models, the best pattern to describe the rise of log HCG was quadratic with the rate of increase slowing at 24 days post-oocyte retrieval. Limiting the analysis to measurements below the discriminatory zone, the linear model adequately characterized the profile. The average slope was 0.403, yielding a predicted increase of 1.50 (50% increase) in 1 day and 2.24 (124%) in 2 days. In the final model, absolute HCG values, but not rate of rise, were significantly higher for twins and triplets and significantly lower for patients with BMI>30 kg/m2. CONCLUSIONS: The HCG profile of viable pregnancies conceived with IVF is quadratic with an earlier plateau than has been reported for non-IVF pregnancies. The average rate of rise is comparable to previous estimates in symptomatic spontaneous conceptions.     

Obstetric outcome of 424 pregnancies after intracytoplasmic sperm injection

An evaluation of the outcome of pregnancies resulting from intracytoplasmicsperm injection for severe male factor infertility was conductedby analysing the data obtained from the patients and/or theirobstetrician/gynaecologist on standardized questionnaires. Thedata from 424 pregnancies between April 1991 and September 1994were analysed. Early pregnancy loss before 16 weeks occurredin 99 cases (23.3%), including 48 clinical abortions (11.3%),47subclinical pregnancies (11.1%) and four ectopic pregnancies(0.9%). Vanishing twins and triplets, which could be regardedas early embryonic wastage, were found in 36 cases (8.5%). Onepregnancy was interrupted at week 15 of gestation because ofanhydramnios, and four pregnancies (0.9%) ended in spontaneouslate abortions before 26 weeks. A total of 320 pregnancies (75.5%)resulted in the birth of at least one child; 222 of these (69.3%)were singletons, 93 were twins (29.1%) and five were triplets(1.6%). The problems of prematurity and low birthweight wereespecially related to the multiplicity of pregnancies. Furthermore,from among the total of 423 babies born, we have observed threecases of stillbirth and five cases of neonatal mortality. Theperinatal mortality rate was therefore 18.9 per 1000 births.The results of this study show that the obstetric outcome ofthese pregnancies was similar to that obtained after conventionalin-vitro fertilization and other assisted reproduction techniques.     

Obstetric and neonatal outcome in women with a history of recurrent miscarriage: a cohort study

Obstetric and neonatal outcomes of women who had a history of recurrent miscarriage were compared with a control population from 1 January 1992 to 30 June 1998. Amongst a total of 162 pregnancies which progressed beyond 24 weeks gestation in women with a history of recurrent miscarriage, there were four perinatal deaths and 16 babies were admitted to the special care baby unit. The rates of preterm delivery (13%), small-for-gestational-age (13%), perinatal loss (2.5%) and Caesarean section (36%) were significantly (P < 0.05) higher than those of the control group (3.9, 2.1, 1 and 16.7% respectively). The ratio of male to female babies was equal. There was no significant difference in the incidence of hypertension or diabetes between the two groups. Patients with recurrent miscarriage represent a population at high risk of obstetric problems and close surveillance in the antenatal period is therefore required.     

Ovarian response to stimulation of HIV-positive patients during IVF treatment: a matched, controlled study

BACKGROUND: Our aim was to compare the ovarian response of HIV-positiveand -negative patients during IVF. METHODS: Setting –HIV and IVF reference university hospital. Twenty-seven HIV-infectedpatients who had undergone IVF between March 2000 and March2005 were matched with 77 HIV-negative patients for age, aetiologyof infertility, whether it was primary or secondary infertility,duration of infertility, history of pelvic surgery and typeof pituitary inhibition. Outcome – poor responders weredefined using one of the following criteria: a cancelled cycle(for insufficient ovarian response), less than four mature follicles(16 mm), peak serum levels of E₂ lower than 1000 pg/ml. RESULTS:There were no differences between the two groups of patientsfor the matched criteria. The proportion of African women andof women with a history of pelvic inflammatory disease was significantlyhigher among HIV patients than among the control group. Withthe exception of a lower number of transferred embryos amongHIV-positive patients versus HIV-negative ones (1.3 versus 1.9;P = 0.035), there was no significant difference between thetwo groups of patients regarding ovarian response parameters.CONCLUSION: HIV-infected patients who are in good general conditionand who are matched to a control group present a similar ovarianresponse to stimulation, suggesting the existence of a similarovarian reserve.     

Vanishing twins: a predictor of small-for-gestational age in IVF singletons

BACKGROUND: The purpose of this study was to assess the effect of a vanishing twin on the risk of being small-for-gestational age (SGA) in in vitro fertilization (IVF) singletons. METHODS: The study included 642 survivors of a vanished co-twin, 5237 primary singletons and 3678 primary twins. The survivor cohort was subdivided according to gestational age at the time of vanishing to give groups of early (<8 weeks), intermediate (8-22 weeks) and late (>22 weeks) survivors. RESULTS: The rate of SGA infants was significantly higher in survivors than in singletons (OR: 1.50, 95%CI: 1.03-2.20) and a significant inverse correlation was observed between SGA and the gestational age at the time of vanishing (r = -0.10, P < 0.02). Also in term infants, the risk of birthweight <2500 g was higher in survivors than in singletons (OR: 1.71, 95%CI: 1.06-2.74). A similar increase in the rate of low birthweight in term survivors was seen with increasing gestational age at the time of vanishing (r = -0.12; P < 0.01). In multiple logistic regression analysis adjusting for maternal age, parity, child gender and pre-eclampsia, the vanishing of a co-twin (OR: 1.56, 95%CI: 1.06-2.27) and gestational age at the time of vanishing (OR: 2.08, 95%CI: 1.00-4.35) were the only significant predictors of being SGA. CONCLUSIONS: IVF singletons with a vanished co-twin had a higher rate of SGA than singletons from a single gestation and the risk of SGA is increased with increasing gestational age at the time of vanishing.     

The obstetric outcome of singleton pregnancies following in-vitro fertilization/gamete intra-Fallopian transfer

The present study compares 465 singleton live deliveries fromin-vitro fertilization/gamete intra-Fallopian transfer (IVF/GIFT)pregnancies with a large control population to evaluate theincidence of pre-term delivery and small for gestational age(SGA) or very small for gestation age (VSGA) babies resultingfrom IVF/GIFT pregnancies. Overall the incidence of SGA or VSGAfrom an IVF/GIFT pregnancy is higher than from the normal obstetricpopulation (SGA odds ratio 1.76, 95% confidence interval (CI):1.38–2.25 and VSGA odds ratio 1.61, 95% CI: 1.05–2.46)particularly among primiparous women (SGA odds ratio 1.99, 95%CI: 1.25–3.16 and VSGA odds ratio 1.97, 95% CI: 1.49–2.62).After stratifying by the cause of infertility, only women withunexplained infertility had a significantly higher proportionof SGA/VSGA babies. There was a significantly higher incidenceof pre-term deliveries among the young primiparae (odds ratio5.02, 95% CI: 3.09–8.13). Thus the excess risk of deliveringa SGA/VSGA baby and pre-term delivery from an IVF/GIFT pregnancyseems to be largely confined to women with unexplained infertilityand young primiparae.     

First-trimester bleeding and pregnancy outcome in singletons after assisted reproduction

BACKGROUND: First-trimester bleeding is frequent in assisted reproductive technique (ART) pregnancies. It is unknown whether first-trimester bleeding, if not ending in a spontaneous abortion, negatively influences further pregnancy outcome in ART in singletons. METHODS: Data were obtained from our ART database (1993-2002), with 1432 singleton ongoing pregnancies being included in this study. The outcome measures-second-trimester and third-trimester bleeding, preterm contraction rates, pregnancy duration, birthweight, Caesarean section rates, intrauterine growth retardation (IUGR), preterm prelabour rupture of membranes (P-PROM), neonatal intensive care unit (NICU) admission and perinatal mortality-were compared in the groups with and without first-trimester bleeding. RESULTS: Significantly more singleton pregnancies resulted from a vanishing twin in the group with first-trimester bleeding (8.7%) than in the controls (4.0%). A correlation was found between the incidence of first-trimester bleeding and the number of embryos transferred. First-trimester bleeding led to increased second-trimester [odds ratio (OR)=4.56; confidence interval (CI)=2.76-7.56] and third-trimester bleeding rates (OR=2.85; CI=1.42-5.73), P-PROM (OR=2.44; CI=1.38-4.31), preterm contractions (OR=2.27; CI=1.48-3.47) and NICU admissions (OR=1.75; CI=1.21-2.54). First-trimester bleeding increased the risk for preterm birth (OR=1.64; CI=1.05-2.55) and extreme preterm birth (OR=3.05; CI=1.12-8.31). CONCLUSIONS: First-trimester bleeding in an ongoing singleton pregnancy following ART increases the risk for pregnancy complications. The association between first-trimester bleeding, the number of embryos transferred and adverse pregnancy outcome provides a further argument in favour of single-embryo transfer.     

Number of embryos for transfer after IVF and ICSI: a Cochrane review

BACKGROUND: The most common complication of IVF is multiple pregnancy, which occurs in 25% of pregnancies following the transfer of two embryos. Single embryo transfer can minimize twin pregnancies but could also lower live birth rates. Our aim was to perform a systematic review of randomized trials to determine the effectiveness of single versus double embryo transfer. METHODS: Cochrane Collaboration review methods were followed. Randomized controlled trials comparing single and double embryo transfers were identified by searching Medline, EMBASE and the Cochrane register of controlled trials. Contents of specialist journals and proceedings from meetings of relevant societies were hand searched. Data were pooled with Rev Man software using the Peto-modified Mantel-Hanzel method. RESULTS: Pooled results from four trials indicate that although double embryo transfer leads to a higher live birth rate per woman [odds ratio (OR) 1.94, 95% confidence interval (CI) 1.47-2.55] in a fresh IVF cycle, comparable results are obtained by subsequent transfer of a frozen embryo (OR 1.19, 95% CI 0.87-1.62). The multiple pregnancy rate is significantly higher (OR 62.83, 95% CI 8.52-463.57) after double embryo transfer. CONCLUSIONS: Single embryo transfer significantly reduces the risk of multiple pregnancy, but also decreases the chance of live birth in a fresh IVF cycle. Subsequent replacement of a single frozen embryo achieves a live birth rate comparable with double embryo transfer.     

Obstetric outcome after prenatal diagnosis in pregnancies obtained after intracytoplasmic sperm injection

In this study we compared the pregnancy outcome of 576 pregnanciesafter prenatal diagnosis with that of 540 pregnancies withoutprenatal diagnosis in our micro-injection programme. Amniocentesiswas suggested for singleton pregnancies (n = 465) and chorionicvillus sampling (CVS) was proposed for twin pregnancies (n =111 pregnancies, 222 fetuses). A total of 365 patients withsingleton pregnancies and 175 patients with twin pregnancieswho did not undergo prenatal diagnosis were selected as controls.Compared with the controls, the odds ratios in the amniocentesisgroup for preterm delivery, low birthweight, very low birthweightand fetal loss were 0.97 [95% confidence interval (CI): 0.60–1.57],1.27 (95% CI: 0.78–2.06), 1.57 (95% CI: 0.53–4.66)and 0.86 (95% CI: 0.32–2.37) respectively. Compared withthe controls, the odds ratios in the CVS group for preterm delivery,low birthweight, very low birthweight and fetal loss were 0.89(95% CI: 0.61–1.30), 1.03 (95% CI: 0.74–1.45), 0.79(95% CI: 0.41–1.53) and 0.47 (95% CI: 0.17–1.30)respectively. We concluded that, in this series of intracytoplasmicsperm injection (ICSI) pregnancies, prenatal testing did notincrease the preterm-delivery, the low-birthweight, or the verylow-birthweight rates as compared with those of the controls.In the prenatal diagnosis group, the fetal loss rate was comparableto that of the control group. Larger prospective controlledstudies are needed in order to inform patients reliably aboutthe risks and the advantages of prenatal testing in ICSI pregnancies.     

Prevention of twin pregnancies after IVF/ICSI by single embryo transfer. ESHRE Campus Course Report

Twin pregnancies constitute the most serious complication for both mother and children after IVF/ICSI treatment, but transfer of at least two 'best looking' embryos remains the standard policy. This is due to our inability and reluctance to identify both the 'twin prone' patient and the top quality embryo. Some centres now electively transfer a single embryo (eSET) when particular embryo quality and patient criteria are met. Results from several centres were presented during an ESHRE Campus Course, held on May 6(th) 2000. Sound clinical trials are needed to clarify several points of discussion. What is the clinical profile of patients in whom eSET should be considered? Will the overall (ongoing) pregnancy rate of the IVF/ICSI programme decrease if eSET is performed in these patients? What is the twinning rate when eSET is a routine policy? Will the financial gain by avoiding perinatal hospitalization costs of prevented twins be balanced by the likely need to perform a number of extra IVF/ICSI cycles? What will be gained by freezing the extra number of high quality embryos? Should eSET be performed at the 2 pronuclear stage, the early cleaving embryo or the blastocyst stage? Common sense dictates that eSET as a concept should be applied from now onwards.     

Safety issues in assisted reproductive technology: aetiology of health problems in singleton ART babies

The frequency of health problems in singleton assisted reproductive technologies (ART) babies is higher than in singletons from spontaneous gestations. Any of the following factors may be involved: in-vitro technology, ovarian stimulatory drugs and infertility itself. A literature review on premature birth, low birth weight, perinatal mortality and major birth defects in children conceived from infertility treatments was conducted. Only publications comparing the outcome of pregnancy in an infertile group of patients to a matched control group were selected. The analysis of the outcome of singleton pregnancies resulting from IVF versus artificial insemination, obtained with or without the use of ovarian stimulatory agents and obtained with or without the use of a semen donor, suggests that female infertility is an important risk factor. Criteria for screening at-risk infertile women have not yet been identified. Prospective studies designed to identify precisely the aetiology of health problems in singletons ART babies will have to be conducted. The absence of criteria correlating at-risk infertile women to health problems in their children does not allow a gynaecologist the opportunity to offer infertility treatments to the least susceptible patients.     

Pregnancy outcome after IVF and ICSI in unexplained, endometriosis-associated and tubal factor infertility

BACKGROUND: This study was undertaken in order to compare pregnancy outcome after IVF and ICSI in unexplained and endometriosis-associated infertility using tubal factor infertility as controls. METHODS: This was a retrospective cohort study of early IVF/ICSI pregnancies verified by serum hCG measurement, comparing the subsequent outcome in unexplained (n = 274) and minimal endometriosis-associated (n = 212) with tubal factor (n = 540) infertility as controls. From January 1990 to December 2002, 1026 conception cycles after treatment with IVF or ICSI complied with the inclusion criteria. RESULTS: Live birth rate, twin birth rate after transfer of two embryos and abortion rate prior to 6 weeks of gestation were superior for the unexplained (78.8, 23.5 and 11.7%) compared to endometriosis-associated (66.0, 15.0 and 19.3%) and tubal factor (66.7, 18.1 and 18.0%) infertility groups (P < 0.05). Compared to the endometriosis-associated, the unexplained infertility group attained a higher pregnancy rate after the first treatment cycle (P < 0.05). CONCLUSIONS: The overall better outcome for the unexplained infertility group with respect to live birth rate, twin birth rate and early abortion rate compared to the minimal peritoneal endometriosis-associated and tubal factor infertility groups might be a guide to select diagnostic groups for single embryo transfer and be useful in patient counselling.