Gestational Duration, and Fetal and Infant Mortality for Twins vs Singletons

The Excess Mortality Among Twins in the Dominican Republic and Haiti Through the Components of Age Under Five: A Comparative Study of Trends and Associated Factors

Despite the decline in mortality rates among children in developing countries, disparities persist between countries, particularly between twins and singletons. This study employed data from nine Demographic and Health Surveys in the Dominican Republic and Haiti to estimate and compare mortality rates for twins and singletons in categories of the under-5 age group (neonatal, postneonatal, and child mortality) and examine the factors associated with excess mortality among twins. From 1996 to 2013, the under-5 mortality rate (U5MR) for singletons in the Dominican Republic declined from 56‰ (95% CI [47, 64) to 30‰ (22-39) and from 108‰ (53-164) to 53‰ (16-89) among twins. In Haiti, between 1994 and 2016, the U5MR declined from 121‰ (109-133) to 77‰ (68-80) for singletons and from 432‰ (327-538) to 204‰ (149-260) among twins. The adjusted risk of neonatal death for twins is 1.4 (1.0-1.9) times higher than for singletons in the Dominican Republic, compared to a risk of 4.3 (3.5-5.3) times higher in Haiti. In the post-neonatal period, the mortality risk for twins in the Dominican Republic was 1.8 (1.0-3.1) times higher than that for singletons, 2.9 (2.3-3.8) in Haiti. The risk of death for twins was not significantly different from that for singletons in both the Dominican Republic and Haiti at ages 1-4 years. Low birth weight, lack of breastfeeding, absence of, or inadequate, antenatal care, noncesarean section birth, and high birth order were associated with excess mortality among twins in both countries.

Granulocyte colony-stimulating factor in assisted reproductive technology treatment does not increase the risk of adverse perinatal outcomes in twin pregnancies

The aim of the study is to compare the perinatal outcomes of twin pregnancies resulting from assisted reproductive technology (ART) treatment in which granulocyte colony-stimulating factor (G-CSF) was used with those in which it was not. In this retrospective study, the clinical data of 122 dichorionic diamniotic twin pregnancies were reviewed. Pregnancies were divided into two groups, G-CSF-treated and non-G-CSF treated. Maternal age, gestational week at birth, oligohydramnios, gestational hypertension, pre-eclampsia, preterm birth, first-trimester bleeding, gestational diabetes, rupture of membrane, foetal congenital anomalies, admission to the neonatal intensive care unit, birth weight (BW), small for gestational age, BW discordance, Apgar score and placental weight were compared between the groups.IMPACT STATEMENTWhat is already known on this subject? Granulocyte colony-stimulating factor (G-CSF) administrations increase pregnancy outcomes and do not have a negative effect on perinatal outcomes in singleton pregnancies.What the results of this study add? This study showed that the perinatal outcome of dichorionic diamniotic twin pregnancies conceived after assisted reproductive technology (ART) treatment was similar in the GSF administrated and non-GSF administrated groups.What the implications are of these findings for clinical practice and/or further research? Using G-CSF to increase the success of ART does not seem to have an adverse outcome in the dichorionic diamniotic twin pregnancies.

The changing impact of assisted reproductive techniques on preterm birth during the period 2007-2020 in Lombardy, Northern Italy

OBJECTIVE

To assess the impact of Assisted Reproductive Techniques (ART) on the risk of preterm birth (PTB).

STUDY DESIGN

This retrospective population-based study used healthcare utilization databases of the Lombardy Region to select all the deliveries occurred between 2007 and 2020. Log-binomial regression models were fitted to estimate prevalence ratio (PR) and the corresponding 95% confidence interval (CI) of PTB among deliveries after ART. Estimates were adjusted for maternal sociodemographic features. Furthermore, the population attributable fraction was computed. All the analyses were performed for calendar period and were repeated excluding multiple births.

RESULTS

In our cohort, an increasing trend in the number of ART emerged, with an overall rate of 25.8 per 1,000 deliveries (N = 28,742). ART was positively related to PTB (aPR = 2.83, 95 % CI: 2.76-2.91) with a downward trend. Over the period study, multiple births after ART decreased (from 20.4 % to 8.4 %) and were constantly burdened by a higher number of PTB. Excluding multiple births, the association was substantially lower (aPR = 1.72, 95 % CI: 1.65-1.79) and did not describe any trend. Moreover, stratifying for type of pregnancy, the association was observed only among singletons. Finally, the proportion of PTB considered attributable to ART increased from about 2-3 % to 6 % till the 2016, then decreased.

CONCLUSION

The investigation suggested that ART was related to PTB; this association may be partly justified by the high rate of multiple births among women who conceived non spontaneously. However, excluding multiple births, ART remained associated with PTB.

Comparison of different types of twin pregnancies in terms of obstetric and perinatal outcomes: association of vanished twins with methylenetetrahydrofolate reductase (MTHFR) polymorphism(s)

PURPOSE

Vanished twin (VT) has been associated with poor perinatal outcomes. Our research aimed to investigate the outcomes of pregnancies with vanished twin and its possible association with methylenetetrahydrofolate reductase (MTHFR) polymorphisms.

METHODS

This study consisted of 30 of 38 VT pregnancies (group 1, VT group), 109 singletons (group 2), 70 spontaneous twins (group 3), and 101 in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) twins (group 4).

RESULTS

Most patients in group 1 (28/30) were tested for MTHFR genes (C677T or A1298C polymorphisms). Eight of the 38 pregnancies with VT (21.1%) resulted in miscarriage. The prevalence of "2 or more pregnancy losses" in the "obstetric history" in group 1 was higher (23.3%) than those in the other groups (p = 0.007, χ² = 17.8). The allelic frequencies of MTHFR 677 and MTHFR 1298 in group 1 were 0.268 and 0.429, respectively (higher than those in healthy population). The median birthweights in groups 1, 2, 3, and 4 were 2940, 3200, 2300, and 2095 g, respectively. The prevalence of respiratory distress syndrome was significantly higher in the IVF/ICSI twin pregnancy group (p < 0.001, χ² = 21.2). Early pregnancy loss and the presence of "2 or more miscarriages" in the obstetric history of pregnancies with VT were more frequent.

CONCLUSION

The coincidence of VT and MTHFR polymorphisms might play an incidental or factual role in this connection.

Association between periconceptional weight loss and maternal and neonatal outcomes in obese infertile women

Background

Obesity in women of reproductive age has deleterious effects on reproductive and offspring health. In this study, we aimed to evaluate the association between the magnitude of periconceptional body-mass index (BMI) change and maternal and neonatal outcomes in obese infertile women who participated in the LIFEstyle study. The LIFEstyle study was a randomized controlled trial, evaluating if a six-month lifestyle intervention program prior to infertility treatment in obese infertile women improved birth rates, compared to prompt infertility treatment.

Methods and findings

This is an exploratory post hoc analysis of the LIFEstyle study. We recorded periconceptional BMI change in women with an ongoing pregnancy, pooling data of all women, regardless of randomization arm. Periconceptional BMI change was calculated using weight at randomization and the periconceptional weight (measured in kilograms 12 weeks before or after conception and expressed as BMI change in units BMI (kg/m²)). Subsequently, women were categorized into quartiles according to the magnitude of their periconceptional change in BMI. The odds of maternal and neonatal outcomes were calculated using logistic regression analysis, comparing women in each of the first three weight change quartiles separately, and combined, to women in the fourth quartile. The fourth quartile was chosen as reference group, since these women had the least weight loss. We adjusted for periconceptional BMI, nulliparity and smoking status. In addition, we performed a subgroup analysis for singleton pregnancies. In the LIFEstyle study, 321 obese infertile women achieved an ongoing pregnancy which was conceived within 24 months after randomization. Periconceptional BMI change was available in 244 of these women (76%). Median BMI at randomization was 35.9 kg/m². Women in the first quartile (Q1) had a periconceptional BMI change of <-2.1 kg/m², women in the second quartile (Q2) -2.1 to -0.9 kg/m², women in the third quartile (Q3) -0.9 to 0.1 kg/m² and women in the fourth quartile (Q4) gained ≥0.1 kg/m². There were no significant differences between women in the quartiles regarding rates of excessive gestational weight gain (in term pregnancies), gestational diabetes, preterm birth, induction of labor, spontaneous vaginal birth and Caesarean section. Compared to women in Q4, the adjusted odds ratios, aOR, and 95% confidence interval for a hypertensive complication were; 0.55 (0.22–1.42) for women in Q1, 0.30 (0.12–0.78) for women in Q2, 0.39 (0.16–0.96) for women in Q3 and 0.39 (0.19–0.82) for women in Q1 to Q3 combined. In the subgroup analysis, investigating singleton pregnancies only, the statistically significant decreased rate of a hypertensive complication remained in women in Q2 (aOR 0.27, 95% CI 0.10–0.72) and Q3 (aOR 0.39, 95%CI 0.16–0.98) and when comparing women in Q1 to Q3 together to women in Q4 (aOR 0.38, 95%CI 0.18–0.80). Furthermore, there was a significantly decreased aOR (95%CI) of preterm birth in women in Q2 (0.24, 0.06–0.98) and when combining women in Q1 to Q3 (0.37, 0.14–0.97) compared to women in Q4.

Conclusions

These results suggest that a periconceptional decrease in BMI in obese infertile women could lead to a decrease of the rates of hypertensive pregnancy complications and preterm birth. The results are limited by the exploratory nature of the analyses and further evidence is necessary to provide more definitive conclusions.

Comparison of conventional 2D ultrasound to magnetic resonance imaging for prenatal estimation of birthweight in twin pregnancy

BACKGROUND

During prenatal follow-up of twin pregnancies, accurate identification of birthweight and birthweight discordance is important to identify the high-risk group and plan perinatal care. Unfortunately, prenatal evaluation of birthweight discordance by 2-dimensional ultrasound has been far from optimal.

OBJECTIVE

The objective of the study was to prospectively compare estimates of fetal weight based on 2-dimensional ultrasound (ultrasound-estimated fetal weight) and magnetic resonance imaging (magnetic resonance-estimated fetal weight) with actual birthweight in women carrying twin pregnancies.

STUDY DESIGN

Written informed consent was obtained for this ethics committee-approved study. Between September 2011 and December 2015 and within 48 hours before delivery, ultrasound-estimated fetal weight and magnetic resonance-estimated fetal weight were conducted in 66 fetuses deriving from twin pregnancies at 34.3-39.0 weeks; gestation. Magnetic resonance-estimated fetal weight derived from manual measurement of fetal body volume. Comparison of magnetic resonance-estimated fetal weight and ultrasound-estimated fetal weight measurements vs birthweight was performed by calculating parameters as described by Bland and Altman. Receiver-operating characteristic curves were constructed for the prediction of small-for-gestational-age neonates using magnetic resonance-estimated fetal weight and ultrasound-estimated fetal weight. For twins 1 and 2 separately, the relative error or percentage error was calculated as follows: (birthweight - ultrasound-estimated fetal weight (or magnetic resonance-estimated fetal weight)/birthweight) × 100 (percentage). Furthermore, ultrasound-estimated fetal weight, magnetic resonance-estimated fetal weight, and birthweight discordance were calculated as 100 × (larger estimated fetal weight-smaller estimated fetal weight)/larger estimated fetal weight. The ultrasound-estimated fetal weight discordance and the birthweight discordance were correlated using linear regression analysis and Pearson's correlation coefficient. The same was done between the magnetic resonance-estimated fetal weight and birthweight discordance. To compare data, the χ², McNemar test, Student t test, and Wilcoxon signed rank test were used as appropriate. We used the Fisher r-to-z transformation to compare correlation coefficients.

RESULTS

The bias and the 95% limits of agreement of ultrasound-estimated fetal weight are 2.99 (-19.17% to 25.15%) and magnetic resonance-estimated fetal weight 0.63 (-9.41% to 10.67%). Limits of agreement were better between magnetic resonance-estimated fetal weight and actual birthweight as compared with the ultrasound-estimated fetal weight. Of the 66 newborns, 27 (40.9%) were of weight of the 10th centile or less and 21 (31.8%) of the fifth centile or less. The area under the receiver-operating characteristic curve for prediction of birthweight the 10th centile or less by prenatal ultrasound was 0.895 (P < .001; SE, 0.049), and by magnetic resonance imaging it was 0.946 (P < .001; SE, 0.024). Pairwise comparison of receiver-operating characteristic curves showed a significant difference between the areas under the receiver-operating characteristic curves (difference, 0.087, P = .049; SE, 0.044). The relative error for ultrasound-estimated fetal weight was 6.8% and by magnetic resonance-estimated fetal weight, 3.2% (P < .001). When using ultrasound-estimated fetal weight, 37.9% of fetuses (25 of 66) were estimated outside the range of ±10% of the actual birthweight, whereas this dropped to 6.1% (4 of 66) with magnetic resonance-estimated fetal weight (P < .001). The ultrasound-estimated fetal weight discordance and the birthweight discordance correlated significantly following the linear equation: ultrasound-estimated fetal weight discordance = 0.03 + 0.91 × birthweight (r = 0.75; P < .001); however, the correlation was better with magnetic resonance imaging: magnetic resonance-estimated fetal weight discordance = 0.02 + 0.81 × birthweight (r = 0.87; P < .001).

CONCLUSION

In twin pregnancies, magnetic resonance-estimated fetal weight performed immediately prior to delivery is more accurate and predicts small-for-gestational-age neonates significantly better than ultrasound-estimated fetal weight. Prediction of birthweight discordance is better with magnetic resonance imaging as compared with ultrasound.

Chromosomal Aberrations in Monozygotic and Dizygotic Twins Versus Singletons in Denmark During 1968–2009

Background: Hall (Embryologic development and monozygotic twinning. Acta Geneticae Medicae et Gemellologiae, Vol. 45, 1996, pp. 53–57) hypothesized that chromosomal aberrations can lead to monozygotic (MZ) twinning. However, twinning and chromosomal aberrations increase prenatal mortality and could reduce the prevalence of chromosomal aberrations in live-born twins. We compared prevalence proportion ratios (PPR) of chromosomal aberrations and trisomy 21 (T21) in live-born twins versus singletons born in Denmark during 1968–2009. Methods: We linked the Danish Twin Registry and a 5% random sample of all singletons to the Danish Cytogenetic Central Register and calculated PPR adjusted for maternal age for MZ, dizygotic (DZ), and all twins versus singletons. Zygosity was based on questionnaires or genetic markers. Results: No overall difference in risk of chromosomal aberrations or T21 in twins versus singletons was found. PPR in MZ and DZ twins was 0.87 (95% CI [0.60, 1.27]) and 1.05 (95% CI [0.88, 1.27]), respectively. For T21 there was a tendency to a lower prevalence in MZ twins compared to singletons (PPR: 0.29, 95% CI [0.07, 1.14]), whereas PPR was significantly increased in DZ twins (1.62, 95% CI [1.20, 2.19]). The observed proportion of MZ twin pairs among twin pairs with aberrations (0.22, 95% CI [0.16, 0.28]) was significantly lower than the proportion expected from the Weinberg method (0.32, 95% CI [CI, 0.26, 0.39]). Conclusion: Based on databases providing complete national coverage on twins with chromosomal aberrations, we found no overall difference in risk of chromosomal aberrations or T21 in twins versus singletons. Around conception twins may have an increased risk of chromosomal aberrations, but loss of especially MZ embryos could lead to similar risk among live-born twins and singletons.

Specialised antenatal clinics for women with a multiple pregnancy for improving maternal and infant outcomes

BACKGROUND

Regular antenatal care for women with a multiple pregnancy is accepted practice, and while most women have an increase in the number of antenatal visits, there is no consensus as to what constitutes optimal care. 'Specialised' antenatal clinics have been advocated as a way of improving outcomes for women and their infants.

OBJECTIVES

To assess, using the best available evidence, the benefits and harms of 'specialised' antenatal clinics compared with 'standard' antenatal care for women with a multiple pregnancy.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 May 2015) and reference lists of retrieved studies.

SELECTION CRITERIA

All published, unpublished, and ongoing randomised controlled trials with reported data that compared outcomes in mothers and babies with a multiple pregnancy who received antenatal care specifically designed for women with a multiple pregnancy (as defined by the trial authors) with outcomes in controls who received 'standard' antenatal care (as defined by the trial authors).

DATA COLLECTION AND ANALYSIS

Two of the review authors independently assessed trials for inclusion and trial quality. Both review authors extracted data. Data were checked for accuracy. We graded the quality of the evidence using GRADEpro software.

MAIN RESULTS

Findings were based on the results of a single study with some design limitations.Data were available from one study involving 162 women with a multiple pregnancy. For the only reported primary outcome, perinatal mortality, we are uncertain whether specialised antenatal clinics makes any difference compared to standard care (risk ratio (RR) 1.02; 95% confidence interval (CI) 0.26 to 4.03; 324 infants, very low quality evidence). Women receiving specialised antenatal care were significantly more likely to birth by caesarean section (RR 1.38; 95% CI 1.06 to 1.81; 162 women, moderate quality evidence). Data were not reported in the study on the following primary outcomes: small-for-gestational age, very preterm birth or maternal death. There were no differences identified between specialised antenatal care and standard care for other secondary outcomes examined: postnatal depression (RR 0.48; 95% CI 0.19 to 1.20; 133 women, very low quality evidence), breastfeeding (RR 0.63; 95% CI 0.24 to 1.68; 123 women, very low quality evidence), stillbirth (RR 0.68; 0.12 to 4.04) or neonatal death (RR 2.05; 95% CI 0.19 to 22.39) (324 infants).

AUTHORS' CONCLUSIONS

There is currently limited information available from randomised controlled trials to assess the role of 'specialised' antenatal clinics for women with a multiple pregnancy compared with 'standard' antenatal care in improving maternal and infant health outcomes. The value of 'specialised' multiple pregnancy clinics in improving health outcomes for women and their infants requires evaluation in appropriately powered and designed randomised controlled trials.

Twins less frequent than expected among male births in risk averse populations

Male twin gestations exhibit higher incidence of fetal morbidity and mortality than singleton gestations. From an evolutionary perspective, the relatively high rates of infant and child mortality among male twins born into threatening environments reduce the fitness of these gestations, making them more vulnerable to fetal loss. Women do not perceive choosing to spontaneously abort gestations although the outcome may result from estimates, made without awareness, of the risks of continuing a pregnancy. Here, we examine whether the non-conscious decisional biology of gestation can be linked to conscious risk aversion. We test this speculation by measuring the association between household surveys in Sweden that gauge financial risk aversion in the population and the frequency of twins among live male births. We used time-series regression methods to estimate our suspected associations and Box-Jenkins modeling to ensure that autocorrelation did not confound the estimation or reduce its efficiency. We found, consistent with theory, that financial risk aversion in the population correlates inversely with the odds of a twin among Swedish males born two months later. The odds of a twin among males fell by approximately 3.5% two months after unexpectedly great risk aversion in the population. This work implies that shocks that affect population risk aversion carry implications for fetal loss in vulnerable twin pregnancies.

Relationship of mode of conception and sex concordance with mortality/morbidity in preterm twins

OBJECTIVE

To assess the association of mode of conception and sex concordance with neonatal outcomes in very preterm twins.

STUDY DESIGN

Twin pairs born at gestational age ≤ 32 weeks and admitted to a Level 3 neonatal intensive care unit (NICU) in 2010-2011 were retrospectively identified from the Canadian Neonatal Network™ database. A composite outcome representing neonatal mortality or any severe morbidity (intraventricular hemorrhage grades ≥ 3 or periventricular leukomalacia, retinopathy of prematurity stages ≥ 3, bronchopulmonary dysplasia, or necrotizing enterocolitis stages ≥ 2) was compared between twins conceived using assisted reproduction technologies (ARTs) or spontaneously (SP), and tested for association with sex concordance in individual-level and pair-wise multivariable logistic regression analyses.

RESULTS

Study subjects included 1,508 twins from 216 ART (53 [25%] male-male, 104 [48%] male-female, and 59 [27%] female-female) and 538 SP (192 [36%] male-male, 123 [23%] male-female, and 223 [41%] female-female) pairs. No statistically significant association was detected between mode of conception and the composite outcome of mortality/morbidities. The composite outcome was significantly higher in same-sex than in opposite-sex twins (OR = 1.68; 95% CI = [1.09, 2.59]). This relationship was most pronounced in ART pairs (OR = 2.25; 95% CI = [1.02, 4.98]), with increased rates in one or both twins from male-male versus opposite-sex ART pairs (OR = 3.0; 95% CI = [1.07, 8.36]).

CONCLUSION

Same-sex pairing was associated with higher mortality/morbidities in very preterm twins admitted to the NICU, and can be used in clinical practice to identify twins at higher risk of adverse neonatal outcomes.

Perinatal Outcome of Twins Compared to Singletons of the Same Gestational Age: A Case-Control Study

Our objective was to determine the perinatal outcome of first- and second-born twins compared to singletons, born at the same gestational age. To that end we conducted a case-control study in Flanders (Northern Belgium). During a 10-year period (01.01.1999–31.12.2008), the entire twin population — 11,154 first- and 11,118 second-born twins (cases) — was compared to 22,228 singletons (controls) with respect to fetal and neonatal (0–27 days) mortality. Only case and control infants of ≥ 500 grams were included, which explained the unequal number of first- and second-born twins. Mothers and their infants of cases and of controls were derived from the Flemish perinatal database and were matched for maternal age and parity, gestational age and gender of the offspring. The main outcome measures were fetal and neonatal mortality according to gestational age. The frequency of fetal death was statistically significantly less frequent in preterm born twins than in singletons, except at term where the reverse was seen in second-born twins compared to controls. After adjustment for congenital malformations, the results stayed unchanged. Below 28 weeks gestation, singletons had a significantly lower neonatal mortality rate than twins that persisted after adjustment for congenital malformations: the first-born twin versus singleton OR 1.71 (1.17–2.51) and second-born versus singleton OR 2.09 (1.43–3.05). Between 28 and 32 weeks, the second-born twin showed a survival advantage over the control singleton. Between 32 and 36 6/7 weeks both twins had a significantly higher survival rate than the corresponding singleton controls. However, after adjustment for congenital malformations, the aforementioned differences between 28 and 36 6/7 weeks disappeared. When at term, twins and singletons had a comparable, though very low, neonatal death rate. These results confirm previous published data. In conclusion, we demonstrated that the neonatal death rate was lower for twins between 32 and 36 weeks (from 28 weeks for the second born twin) when compared to a singleton of the same gestational age. After adjusting for congenital malformations, there was no statistical significant difference.

Embryogenesis of chimeras, twins and anterior midline asymmetries

Human spontaneous chimerism, with one body built from cells of both twins of a dizygotic (DZ) pair, is supposed to be extremely rare, arising from the exchange of blood cells through placental anastomoses. Mosaicism is supposed to be far more common, arising from single zygotes by embryonic mutation. Because typical diagnosis of mosaicism can neither identify nor exclude chimerism, 'mosaicism' may often be chimerism undiscovered. Evidence shows chimerism arises primarily from DZ embryo fusion and is not rare, although it has negligible probability under the hypothesis of independent double ovulation and independent embryogenesis. If, instead, DZ twin embryos begin development as a single cell mass, chimerism is likely. This would be consistent with observations that DZ twins develop as differently from singletons as monozygotic twins do with regard to embryogenic establishment of asymmetries of midline neural-crest-driven structures of brain, face and heart. Chimerism is a significant component of human embryonic development that deserves closer attention as a mechanism of developmental variation. The 'common knowledge' understanding of twinning mechanisms is at best inadequate. The importance of the difference lies in what we can learn from chimerism about human embryogenesis and the cellular origins of structures and functions basic to the business of becoming human.

Single embryo transfer and IVF/ICSI outcome: a balanced appraisal

This review considers the value of single embryo transfer (SET) to prevent multiple pregnancies (MP) after IVF/ICSI. The incidence of MP (twins and higher order pregnancies) after IVF/ICSI is much higher (approximately 30%) than after natural conception (approximately 1%). Approximately half of all the neonates are multiples. The obstetric, neonatal and long-term consequences for the health of these children are enormous and costs incurred extremely high. Judicious SET is the only method to decrease this epidemic of iatrogenic multiple gestations. Clinical trials have shown that programmes with >50% of SET maintain high overall ongoing pregnancy rates ( approximately 30% per started cycle) while reducing the MP rate to <10%. Experience with SET remains largely European although the need to reduce MP is accepted worldwide. An important issue is how to select patients suitable for SET and embryos with a high putative implantation potential. The typical patient suitable for SET is young (aged <36 years) and in her first or second IVF/ICSI trial. Embryo selection is performed using one or a combination of embryo characteristics. Available evidence suggests that, for the overall population, day 3 and day 5 selection yield similar results but better than zygote selection results. Prospective studies correlating embryo characteristics with documented implantation potential, utilizing databases of individual embryos, are needed. The application of SET should be supported by other measures: reimbursement of IVF/ICSI (earned back by reducing costs), optimized cryopreservation to augment cumulative pregnancy rates per oocyte harvest and a standardized format for reporting results. To make SET the standard of care in the appropriate target group, there is a need for more clinical studies, for intensive counselling of patients, and for an increased sense of responsibility in patients, health care providers and health insurers.

Preterm delivery

Preterm delivery and its short-term and long-term sequelae constitute a serious problem in terms of mortality, disability, and cost to society. The incidence of preterm delivery, which has increased in recent years, is associated with various epidemiological and clinical risk factors. Results of randomised controlled trials suggest that attempts to reduce these risk factors by use of drugs are limited by side-effects and poor efficacy. An improved understanding of the physiological pathways that regulate uterine contraction and relaxation in animals and people has, however, helped to define the complex processes that underlie parturition (term and preterm), and has led to new scientific approaches for myometrial modulation. The continuing elucidation of the mechanisms that regulate preterm labour, combined with rigorous clinical assessment, offer hope for future solutions.