A comparative study of twinning and triplet rates in 17 countries, 1972-1996

Community perceptions on causes of high dizygotic twinning rate in Igbo-Ora, South-west Nigeria: A qualitative study

BACKGROUND

Dizygotic (DZ, non-identical) twinning rates vary widely across different regions in the world. With a DZ twinning rate of 45 per 1000 live births, Igbo-Ora Community in South-west Nigeria has the highest dizygotic (DZ) twinning rate in the world. Although several postulations exist on the causes of high DZ twinning rates in Igbo-Ora, no study has yet been conclusive on a definite causative agent.

OBJECTIVE

Using qualitative methods, this study explored the perceptions and beliefs of Igbo-Ora residents about the causes of high DZ twinning rates.

METHODS

Focus group discussion sessions and key informant interviews were organized among fathers and mothers of twins, those without twins, and health care providers. Key informant interviews were also held with persons considered to be custodians of culture who may have knowledge relevant to twinning such as traditional rulers, and traditional birth attendants; as well as health care providers, mothers and fathers of twins, and adult twins.

RESULTS

The results showed three factors featuring as the leading perceived causes of twinning in the community. These included twinning being an act of God, hereditary, and being due to certain foods consumed in the community. Contrary to reports that the consumption of a species of yam (Dioscorea rotundata) may be responsible for the DZ twinning in this Community; yam was not prioritized by the respondents as associated with twinning. In contrast, participants repeatedly mentioned the consumption of "ilasa" a soup prepared with okra leaves (Abelmoschus esculenta) with water that is obtained from the community, and "amala" a local delicacy produced from cassava (Manihot esculenta) as the most likely dietary factors responsible for twinning in the community.

CONCLUSION

Since the same foods are consumed in neighboring communities that have lower rates of twinning, we conjecture that nutritional and other environmental factors may produce epigenetic modifications that influence high DZ twinning rates in Igbo-Ora community. We conclude that more directed scientific studies based on these findings are required to further elucidate the etiology of the high rate of DZ twinning in Igbo-Ora.

Co-bedding in neonatal nursery for promoting growth and neurodevelopment in stable preterm twins

BACKGROUND

The increased birth rate of twins during recent decades and the improved prognosis of preterm infants have resulted in the need to explore measures that could optimize their growth and neurodevelopmental outcomes. It has been postulated that co-bedding simulates twins' intrauterine experiences in which co-regulatory behaviors between them are observed. These behaviors are proposed to benefit twins by reducing their stress, which may promote growth and development. However, in practice, uncertainty surrounds the benefit-risk profile of co-bedding.

OBJECTIVES

We aimed to assess the effectiveness of co-bedding compared with separate (individual) care for stable preterm twins in the neonatal nursery in promoting growth and neurodevelopment and reducing short- and long-term morbidities, and to determine whether co-bedding is associated with significant adverse effects.As secondary objectives, we sought to evaluate effects of co-bedding via the following subgroup analyses: twin pairs with different weight ranges (very low birth weight [VLBW] < 1500 grams vs non-VLBW), twins with versus without significant growth discordance at birth, preterm versus borderline preterm twins, twins co-bedded in incubator versus cot at study entry, and twins randomized by twin pair versus neonatal unit.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review Group (CNRG). We used keywords and medical subject headings (MeSH) to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 2), MEDLINE (via PubMed), EMBASE (hosted by EBSCOHOST), the Cumulative Index to Nursing and Allied Health Literature (CINAHL), and references cited in our short-listed articles, up to February 29, 2016.

SELECTION CRITERIA

We included randomized controlled trials with randomization by twin pair and/or by neonatal unit. We excluded cross-over studies.

DATA COLLECTION AND ANALYSIS

We extracted data using standard methods of the CNRG. Two review authors independently assessed the relevance and risk of bias of retrieved records. We contacted the authors of included studies to request important information missing from their published papers. We expressed our results using risk ratios (RRs) and mean differences (MDs) when appropriate, along with 95% confidence intervals (95% CIs). We adjusted the unit of analysis from individual infants to twin pairs by averaging measurements for each twin pair (continuous outcomes) or by counting outcomes as positive if developed by either twin (dichotomous outcomes).

MAIN RESULTS

Six studies met the inclusion criteria; however, only five studies provided data for analysis. Four of the six included studies were small and had significant limitations in design. As each study reported outcomes differently, data for most outcomes were effectively contributed by a single study. Study authors reported no differences between co-bedded twins and twins receiving separate care in terms of rate of weight gain (MD 0.20 grams/kg/d, 95% CI -1.60 to 2.00; one study; 18 pairs of twins; evidence of low quality); apnea, bradycardia, and desaturation (A/B/D) episodes (RR 0.85, 95% CI 0.18 to 4.05; one study; 62 pairs of twins; evidence of low quality); episodes in co-regulated states (MD 0.96, 95% CI -3.44 to 5.36; one study; three pairs of twins; evidence of very low quality); suspected or proven infection (RR 0.84, 95% CI 0.30 to 2.31; three studies; 65 pairs of twins; evidence of very low quality); length of hospital stay (MD -4.90 days, 95% CI -35.23 to 25.43; one study; three pairs of twins; evidence of very low quality); and parental satisfaction measured on a scale of 0 to 55 (MD -0.38, 95% CI -4.49 to 3.73; one study; nine pairs of twins; evidence of moderate quality). Although co-bedded twins appeared to have lower pain scores 30 seconds after heel lance on a scale of 0 to 21 (MD -0.96, 95% CI -1.68 to -0.23; two studies; 117 pairs of twins; I(2) = 75%; evidence of low quality), they had higher pain scores 90 seconds after the procedure (MD 1.00, 95% CI 0.14 to 1.86; one study; 62 pairs of twins). Substantial heterogeneity in the outcome of infant pain response after heel prick at 30 seconds post procedure and conflicting results at 30 and 90 seconds post procedure precluded clear conclusions.

AUTHORS' CONCLUSIONS

Evidence on the benefits and harms of co-bedding for stable preterm twins was insufficient to permit recommendations for practice. Future studies must be adequately powered to detect clinically important differences in growth and neurodevelopment. Researchers should assess harms such as infection, along with medication errors and caregiver satisfaction.

Co-bedding in neonatal nursery for promoting growth and neurodevelopment in stable preterm twins

BACKGROUND

With the increased birth rate of twins during the recent decades and improved prognosis of preterm infants, there is a need to explore measures that could optimise their growth and neurodevelopmental outcomes. It has been postulated that co-bedding simulates the twins' intrauterine experiences in which co-regulatory behaviours between the twins are observed. These behaviours are proposed to benefit the twins by reducing their stress, which may promote growth and development. However, uncertainties exist on the benefit-risk profile of co-bedding in practice.

OBJECTIVES

We aimed to assess the effects of co-bedding on growth, and other clinically relevant physiological and neurodevelopmental outcomes for stable preterm twins.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review Group (CNRG). We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2012, Issue 7), MEDLINE (via PubMed), EMBASE (hosted by EBCHOST), CINAHL and references cited in our shortlisted articles using keywords and MesH headings, up to July 2012.

SELECTION CRITERIA

We included randomised controlled trials with randomisation either at the level of each twin pair and/or at the level of neonatal unit. We excluded cross-over studies.

DATA COLLECTION AND ANALYSIS

We extracted data using the standard methods of the CNRG. Two review authors independently assessed the relevance and risk of bias of the retrieved records. We contacted the authors of the included studies if important information was missing from their published papers. We expressed our results using risk ratio (RR) and mean difference (MD) where appropriate with their 95% confidence intervals (CIs). We adjusted the unit of analysis from individual infants to twin pairs by averaging the measurement for each twin pair (continuous outcome) or by counting the outcome as positive if any of the twins developed the outcome (dichotomous outcome).

MAIN RESULTS

Five studies met the inclusion criteria; however, data were only available for analysis in four studies. Four of the five included studies were small and had significant limitations in design. As each study reported the outcomes differently, data for most of the outcomes were effectively contributed by a single study. There were no differences between co-bedded twins and twins that received separate care in the rate of weight gain (MD 0.20 grams/kg/day, 95% CI: -1.60 to 2.00), apnoea, bradycardia and desaturation (A/B/D) episodes (RR: 0.85, 95% CI: 0.18 to 4.05; 1 study), length of hospital stay (MD -4.90 days, 95% CI: -35.23 to 25.43) and infection rates (typical RR: 0.84, 95% CI: 0.30 to 2.31; 3 studies). There were also no differences in parental perceptions of care. Co-bedded twins appeared to spend more time crying, but they also seemed to spend more time in quiet sleep. There was low or very low quality of evidence across all the outcomes.

AUTHORS' CONCLUSIONS

There was insufficient evidence on the benefits and harms of co-bedding stable preterm twins to make any recommendation in practice. There is a need for future studies that are adequately powered to detect clinically important differences in growth and neurodevelopment. Such studies should also assess harms including infections and medication errors, and caregiver satisfaction.

Frequency of Twin Births in Developed Countries

Twinning rates in developed countries have recently registered an increase. At the end of the 1970s, the change in mother's age structure has partially contributed to the growth in the proportion of multiple births. In fact, the evolution of twinning rates is related to the calendar of maternity since, comparatively to younger mothers, older women more frequently have twins. Moreover, the growing frequency of multiple births also depends on fertility treatments, which are largely used in the developed countries. National data from the civil birth registration systems are taken into account in order to describe, in a comparative study, the main trends of twinning rates in the 20th century.

Changes in Twinning Rates in South Korea: 1981–2002

The present study investigates the twinning rate trends in South Korea for the years 1981 to 2002 utilizing the birth record data from the South Korea National Statistical Office. The twinning rates between 1981 and 1991 remained nearly constant and were slightly less than 10 twin individuals, that is, approximately five pairs per thousand births. Since the early 1990s, however, the twinning rate has increased sharply and reached 19.30 twin individuals, that is, around 10 pairs per thousand births in the year 2002. Application of the Weinberg method to birth data for the years 2000 to 2002 revealed that the dizygotic twin rate in South Korea increased almost threefold between 1981 to 1991 and 2002. In the 1980s the effect of maternal age on twinning rates appeared to be minimal. In the 1990s, however, increases in twinning rates occurred more markedly among older mothers than among younger mothers. We speculate that the rapid rise in twinning rates in South Korea in the 1990s is probably attributable to the spread of Assisted Reproductive Technologies among older mothers who seek treatments for infertility. The present study also examined whether residing in industrial areas is associated with multiple births in the South Korean population. The results did not support the recent finding of higher twinning incidence in industrialized regions.

Demographic and medical consequences of the postponement of parenthood

BACKGROUND Across the developed world couples are postponing parenthood. This review assesses the consequences of delayed family formation from a demographic and medical perspective. One main focus is on the quantitative importance of pregnancy postponement. METHODS Medical and social science databases were searched for publications on relevant subjects such as delayed parenthood, female and male age, fertility, infertility, time to pregnancy (TTP), fetal death, outcome of medically assisted reproduction (MAR) and mental well-being. RESULTS Postponement of parenthood is linked to a higher rate of involuntary childlessness and smaller families than desired due to increased infertility and fetal death with higher female and male age. For women, the increased risk of prolonged TTP, infertility, spontaneous abortions, ectopic pregnancies and trisomy 21 starts at around 30 years of age with a more pronounced effects >35 years, whereas the increasing risk of preterm births and stillbirths starts at around 35 years with a more pronounced effect >40 years. Advanced male age has an important but less pronounced effect on infertility and adverse outcomes. MAR treatment cannot overcome the age-related decline in fecundity. CONCLUSIONS In general, women have partners who are several years older than themselves and it is important to focus more on the combined effect of higher female and male age on infertility and reproductive outcome. Increasing public awareness of the impact of advanced female and male age on the reproductive outcome is essential for people to make well-informed decisions on when to start family formation.

Twin Town in South Brazil: a Nazi's experiment or a genetic founder effect?

Cândido Godói (CG) is a small municipality in South Brazil with approximately 6,000 inhabitants. It is known as the “Twins' Town” due to its high rate of twin births. Recently it was claimed that such high frequency of twinning would be connected to experiments performed by the German Nazi doctor Joseph Mengele. It is known, however, that this town was founded by a small number of families and therefore a genetic founder effect may represent an alternatively explanation for the high twinning prevalence in CG. In this study, we tested specific predictions of the “Nazi's experiment” and of the “founder effect” hypotheses. We surveyed a total of 6,262 baptism records from 1959–2008 in CG catholic churches, and identified 91 twin pairs and one triplet. Contrary to the “Nazi's experiment hypothesis”, there is no spurt in twinning between the years (1964–1968) when Mengele allegedly was in CG (P = 0.482). Moreover, there is no temporal trend for a declining rate of twinning since the 1960s (P = 0.351), and no difference in twinning among CG districts considering two different periods: 1927–1958 and 1959–2008 (P = 0.638). On the other hand, the “founder effect hypothesis” is supported by an isonymy analysis that shows that women who gave birth to twins have a higher inbreeding coefficient when compared to women who never had twins (0.0148, 0.0081, respectively, P = 0.019). In summary, our results show no evidence for the “Nazi's experiment hypothesis” and strongly suggest that the “founder effect hypothesis” is a much more likely alternative for explaining the high prevalence of twinning in CG. If this hypothesis is correct, then this community represents a valuable population where genetic factors linked to twinning may be identified.

Twenty-six triplet pregnancies: a retrospective analysis

METHODS

Twenty-six triplet pregnancies were delivered over 6 years.

RESULTS

Over 80% of pregnancies resulted after infertility treatment (21/26). Mean maternal age was 32. On average, the infants were delivered after 32 + 0 weeks; in 4 cases delivery was at <28 weeks. In 1 case, the leading triplet was delivered spontaneously, the remaining babies by Caesarean. Main indications for Caesarean were: premature membrane rupture, premature contractions, maternal hospitalisation for foetal lung maturation/tocolysis/antibiotics. Mean birth weights were (triplet I-III): 1,730, 1,630 and 1,550 g. Hydrops fetalis and renal agenesis resulted in IUFD of the leading triplet in two cases. All newborns were cared for by neonatology.

CONCLUSIONS

Triplet pregnancies are challenging for all specialities involved. They should be managed from an early stage in cooperation with an experienced centre, allowing outpatient care for as long as possible if there are no complications. This also has a cost-reducing impact.

Dizygotic twinning

The tendency to conceive spontaneous dizygotic (DZ) twins is a complex trait with important contributions from both environmental factors and genetic disposition. Twins are relatively common and occur on average 13 times per 1000 maternities, though the twinning frequency varies over time and geographic location. This variation is mostly attributed to the differences in DZ twinning rate, since the monozygotic twinning rate is relatively constant. DZ twinning is in part under genetic control, with mothers of DZ twins reporting significantly more female family members with DZ twins than mothers of monozygotic twins. Maternal factors such as genetic history, advanced age and increased parity are known to increase the risk of DZ twins. Recent research confirmed that taller mothers and mothers with a high body mass index (30>) are at greater risk of DZ twinning. Seasonality, smoking, oral contraceptive use and folic acid show less convincing associations with twinning. Genetic analysis is beginning to identify genes contributing to the variation in twinning. Mutations in one of these genes (growth differentiation factor 9) are significantly more frequent in mothers of DZ twins. However, the mutations are rare and only account for a small part of the genetic contribution for twinning.

Twin pregnancy as a risk factor for mother-to-child transmission of HIV-1: trends over 20 years

OBJECTIVE

We investigated whether twin pregnancies were at increased risk of mother-to-child HIV-1 transmission (MTCT), in comparison with singletons.

METHODS

Among HIV-1 infected women enrolled in the French Perinatal HIV Cohort (n = 9262), we studied the association between twin deliveries and MTCT rate according to three time periods (pre-1994, 1994-1996, 1997-2004) and the effect of birth order. The mother was considered to have transmitted if at least one of the twins was infected. Univariate and multivariate analyses of risk factors for MTCT were performed for deliveries in the periods up to 1996.

RESULTS

Overall, 2.1% (192/9262) of all the deliveries were twins. The rate of prematurity was greater in twins than in singletons (54% and 13%, respectively). Up to 1996 the rate of MTCT of HIV-1 was 28.3% (15/53) in twin pregnancies, versus 13.5% (414/3077) in singletons [odds ratio (OR), 2.5; 95% confidence interval (CI), 1.4-4.7; P = 0.002; adjusted OR, 2.3: 95% CI, 1.1-2.3; P = 0.03). In the period from 1997 to 2003, MTCT was low and did not differ between twins (1.0%) and singletons (1.8%; P = 1.0). Overall, the transmission rate for the first-born child was threefold that for the second-born child (14/164, 8.5% versus 4/164, 2.4%; P = 0.008).

CONCLUSION

Twin pregnancies were at increased risk of transmission, but in the era of HAART this risk was reduced for twins, as well as singletons. Management of multiple pregnancies should take into account the risks of premature rupture of the membranes and preterm delivery.

Infertility, infertility treatment and twinning: the Danish National Birth Cohort

BACKGROUND

We have previously observed that an increasing time to pregnancy (TTP) is associated with a reduced frequency of twin deliveries in couples not receiving infertility treatment. By using updated information, we assessed the frequencies of dizygotic (DZ) and monozygotic (MZ) twin deliveries as a function of infertility (TTP > 12 months), as well as infertility treatment.

METHODS

From the Danish National Birth Cohort (1997-2003), we identified 51 730 fertile couples with TTP <or= 12 months, 5838 infertile couples who conceived naturally with TTP > 12 months and 5163 infertile couples who conceived after treatment. Information on zygosity, available for part of the cohort (1997-2000), was based on standardized questions on the similarities between the twins at the age of 3-5 years.

RESULTS

Compared with fertile couples, the frequency of DZ twin deliveries was lower for infertile couples conceiving naturally (odds ratio 0.4, 95% confidence interval 0.2-0.7) and was much higher for infertile couples conceiving after treatment (17.3, 14.4-20.7). The frequency of DZ twin deliveries decreased with TTP in untreated couples, whereas the frequency of MZ twin deliveries remained constant.

CONCLUSIONS

The frequency of DZ twin deliveries decreased with TTP and substantially increased with infertility treatment, whereas MZ twin deliveries remained substantially unchanged.

The vanishing twin: a major determinant of infant outcome in IVF singleton births

This article attempts to assess the frequency of vanishing twins in assisted reproductive and spontaneously conceived pregnancies, including in-vitro fertilization (IVF), and its impact on the live-born surviving twin.

Risk of cerebral palsy in multiple pregnancies

Multiple compared with singleton gestations have a five- to tenfold increased risk of CP. The increased risk associated with MC placentation has been variously ascribed to transfer of thromboplastin or thromboemboli from the dead to the surviving fetus, exsanguination of the surviving fetus into the low pressure reservoir of the dead fetus, or hemodynamic instability with bidirectional shunting of blood between the two fetuses. An increased risk of CP in assisted reproductive technology gestations is to be expected because of the higher proportion of preterm births. The increase in risk of CP associated with monochorionic placentation will not be observed except for the minority of assisted reproductive technology gestations that undergo monozygotic splitting.

Reference curves of symphysis-fundus height in twin pregnancies

OBJECTIVE

To generate reliable new reference ranges for symphysis-fundus height (SFH) in twin pregnancies using modern statistical methods and to evaluate whether small-for-gestational age (SGA) babies of women who had a SFH measurement after the 25th gestational week could be predicted by the SFH measurement in the reference curves and other maternal data.

STUDY DESIGN

In a retrospective cross-sectional study at the obstetric outpatient clinic, Zurich University Hospital, SFH was determined in 257 twin-pregnant women with accurately dateable twin pregnancies (Caucasians: N=217, Asians: N=15, Blacks: N=10, and 15 others). Exclusion criteria were intrauterine fetal death, and known fetal and maternal diseases, which influence SFH. Pregnant women with twins were divided in three groups according to the birth weight of the babies. Group I: both babies were appropriate for gestational age (AGA), group II: one baby was AGA and one SGA, and group III: both babies were SGA.

RESULTS

SFH measurements increased linearly with gestational age (GA). The following rule of thumb is suggested for the 50th centile of SFH (cm)=gestational week+10% of gestational week. Age, height, weight and body mass index (BMI) before pregnancy, parity and ethnic group were insignificant determinants in SFH measurement. A prognostic score for identification of group III was created for a GA> or =25 weeks and BMI<30 kg/m2.

CONCLUSIONS

Measuring SFH is simple, inexpensive and non-invasive and may be of some use for identifying twin mothers with SGA twin pairs.

IVF/ICSI twin pregnancies: risks and prevention

Since the 1970s, the national twin birth rates have been increasing worldwide. Apart from the increasing childbearing age, the main cause is the use of assisted reproductive technologies (ART). To explore the overall consequences of dual embryo transfer (DET), the literature has been reviewed systematically regarding short- and long-term outcomes of IVF/ICSI twin pregnancies i.e. pregnancy complications, maternal risks, obstetric outcome and long-term morbidity including neurological sequelae, cognitive development and family implications. Another consequence of DET is vanishing twins, which seems to be a possible cause of adverse outcome in IVF singletons. The sparse literature on vanishing twins in IVF pregnancies and the influence on the surviving co-twin were also addressed. Finally, to determine the effects of implementing elective single embryo transfer (eSET), trials concerning eSET versus DET were analysed. In the light of the steadily increasing twin birth rates and the findings in this overview, where IVF/ICSI twins carry adverse outcome, it should be emphasized that the major obstacle in IVF remains the high twin birth rate. Furthermore vanishing twins account for another hazard of DET. These problems can be resolved by implementing eSET, diminishing the twin birth rate without affecting the overall goal of achieving a healthy infant.

Risk of cerebral palsy in multiple pregnancies

Multiple compared with singleton gestations have a five- to tenfold increased risk of CP. The increased risk associated with MC placentation has been variously ascribed to transfer of thromboplastin or thromboemboli from the dead to the surviving fetus, exsanguination of the surviving fetus into the low pressure reservoir of the dead fetus, or hemodynamic instability with bidirectional shunting of blood between the two fetuses. An increased risk of CP in assisted reproductive technology gestations is to be expected because of the higher proportion of preterm births. The increase in risk of CP associated with monochorionic placentation will not be observed except for the minority of assisted reproductive technology gestations that undergo monozygotic splitting.

Neonatal outcome in a Danish national cohort of 8602 children born after in vitro fertilization or intracytoplasmic sperm injection: the role of twin pregnancy

BACKGROUND

In Denmark, 4% of all infants are born after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) and 40% of these children are twins.

METHODS

We investigated neonatal outcome in a complete Danish IVF/ICSI birth cohort including 8602 infants born between 1995 and 2000: 3438 twins (40%) and 5164 singletons (60%). Births conceived after IVF or ICSI were identified by record linkage with the Danish IVF Registry and the National Medical Birth Registry. Data on neonatal outcome were collected from the National Patient Registry.

RESULTS

IVF/ICSI twins had a 10-fold increased age- and parity-adjusted risk of delivery before 37 completed weeks [odds ratio (OR) 9.9, 95% confidence interval (95% CI) 8.7-11.3] and a 7.4-fold increased risk of delivery before 32 completed weeks (OR 7.4, 95% CI 5.6-9.8) compared with singletons. Correspondingly, ORs of birthweight <2500 g and birthweight <1500 g in twins were 11.8 (95% CI 10.3-13.6) and 5.4 (95% CI 4.1-7.0), respectively. The stillbirth rate was doubled in twins (13.1/1000) compared with singletons (6.6/1000) (p = 0.002). The risk of cesarean section and of admittance to a neonatal intensive care unit (NICU) was 4.6- and 1.8-fold higher in IVF/ICSI twins than in singletons. The rate of major malformations was 40.4/1000 in twins and 36.8/1000 in singletons (p = 0.4), whereas the total malformation rate (major + minor) was higher in twins (73.7/1000) than in singletons (55.0/1000) (p = 0.001). After exclusion of patent ductus arteriosus (PDA), which is strongly associated with preterm birth, no significant differences in any malformation rates were observed between twins and singletons. Apart from the frequency of ICSI children with hypospadias, which reached a significance level of p = 0.05, malformation rates in ICSI children were similar to those in IVF children.

CONCLUSIONS

This study indicates that neonatal outcome in IVF/ICSI twins is considerably poorer than in singletons. Thus, the impact is to draw the attention of clinicians to the benefit of elective single embryo transfer (eSET).

Triplets and quadruplets in Switzerland: comparison with singletons, and evolution over the last decade

AIMS

Main objectives were 1) to determine the incidence of higher multiple births from 1995 to 1998 in Switzerland, and 2) to evaluate neonatal mortality and morbidity. Secondary objectives were 3) to compare the results with those of matched singletons, and 4) to compare the present data to the first Swiss study (1985-1988).

METHODS

Retrospective analysis of maternal and neonatal data obtained from all Swiss hospitals.

RESULTS

The incidence of triplet births was 1/3247 and that of quadruplet births 1/81,186. The median gestational age was 32 5/7 weeks for triplets, and 28 6/7 weeks for quadruplets. The median birth weight was 1665 g for triplets and 1076 g for quadruplets. Perinatal mortality was 6% for triplets and 19% for quadruplets. Respiratory distress syndrome was the major morbidity as diagnosed in 52% of triplets and 81% of quadruplets. A comparison of triplets with matched singletons showed no significant differences in morbidity and mortality. Compared with the first Swiss study, the mortality rate decreased, while the incidence of triplets increased but decreased for quadruplets.

CONCLUSION

The incidence of higher-order multiple births in Switzerland dropped for quadruplets in the last decade but has increased for triplets. The mortality and morbidity of triplets is comparable to that of singletons with a similar gestational age.

Changes in twinning rate: Italy 1950-1996

BACKGROUND

In the wide-ranging debate about the potential monitors of population fertility, twinning rate has been considered a candidate. In the developed countries, a decline in spontaneous twinning rate began around 1950 and continued until the late 1970s. The decrease in mean maternal age at delivery and the number of children per family have been considered as possible reasons for the decrease. The rise in twinning rates, which began in the 1980s, is probably due to the spread of assisted reproduction, at least for older mothers.

METHODS

The temporal trend in twinning rate and the relationship with maternal age at delivery and birth order in the Italian population were analysed.

RESULTS

The recent increase in twinning rate can be mainly attributed to the recourse to assisted reproduction techniques, as demonstrated by the twinning frequency among older primiparae. The twinning rate recently observed in young mothers approximates to the value of the 1950s, which is assumed to represent a 'natural' fertility condition.

CONCLUSIONS

On the assumption that twinning is an indicator of fertility, and hence of population fitness, the present data seem to suggest that natural fertility has been slightly increasing in the Italian population.

Trends in the occurrence, determinants, and consequences of multiple births

After a substantial decrease in the middle of the 20th century, multiple pregnancy rates have increased in many Western countries. Between the mid-1970s and 1998, the rate of twin pregnancies increased by 50% to 60% in England and Wales, France, and the United States. The rates of triplet or higher-order multiple pregnancies increased by 310% in France, 430% in England and Wales, and 696% in the United States. One fourth to one third of the increase in twin or triplet pregnancies are attributable to a contemporaneous increase in maternal age. Furthermore, in countries with high occurrence of multiple births, 30% to 50% of twin pregnancies and at least 75% of triplet pregnancies occur after infertility treatment. The impact of the increase in multiple births on preterm delivery rates in the overall population is mainly attributable to twin pregnancies. In Canada, France, and the United States, an increase in preterm births among multiples contributed almost as much as the increase in occurrence of multiple births to the increase or stabilization of the overall rates of preterm delivery observed in these countries.

Higher order multiple pregnancies in New South Wales 1990-1999

OBJECTIVE

To examine higher order multiple pregnancy and birth rates in NSW, and to describe trends in the characteristics and management of these births.

DESIGN

Cross-sectional analytic study.

SETTING

New South Wales, Australia.

POPULATION

Two hundred and ninety-one women who gave birth to triplets, quadruplets or quintuplets (880 babies) from 1 January 1990 to 31 December 1999.

METHODS

Data were obtained from the NSW Midwives Data Collection and rates over time were calculated.

MAIN OUTCOME MEASURES

Higher order multiple birth and pregnancy rates (> or = 20 weeks), place of birth, mode of delivery, fetal death rates and Apgar scores.

RESULTS

There was no significant change in the number or rate of higher order multiple births in NSW during the 1990s with an average annual rate of 10.3/10,000 births or 3.5/10,000 pregnancies > or = 20 weeks. Among women with higher order multiple pregnancies, those aged > or = 35 years increased from 19% in 1990 to 47% in 1999. There was also a trend towards delivery in a perinatal centre from 56% to 70%, and vaginal birth from 18% to 28%. There were no significant changes in infant outcomes.

CONCLUSIONS

The increases in higher order multiple pregnancies observed in Australia in the 1980s, and into the 1990s in other countries, have not persisted in NSW, suggesting that guidelines for limiting the number of embryos/oocytes transferred in assisted reproductive technologies have been widely adopted.

Transfer of two embryos instead of three will not compromise pregnancy rate but will reduce multiple pregnancy rate in an assisted reproduction unit

OBJECTIVE

To compare the pregnancy rates and multiple pregnancy rates of cycles initiated in 1998 and in 1999, during which 3 and 2 embryos were advised to be replaced, respectively.

STUDY DESIGN

A retrospective study

RESULTS

There were no differences between 1998 and 1999 in the pregnancy rate per cycle started or per transfer, implantation rate and the multiple pregnancy rates, despite a significantly lower number of embryos replaced in 1999. A significantly higher implantation rate was found in cycles with frozen embryos than those without. Using logistic regression analysis, the chance of pregnancy was significantly improved only by the presence of frozen embryos in the fresh cycles with an odds ratio of 2.0 (95% confidence interval: 1.3-3.0) whereas the chance of multiple pregnancy was significantly increased by replacing 3 embryos instead of 2 (odds ratio: 2.1, 95% confidence interval: 1.1-4.2).

CONCLUSION

Patients should be advised to have 2 embryos replaced without jeopardizing the pregnancy rates in the fresh cycles. The risk of multiple pregnancy is significantly increased when 3 embryos are transferred instead of 2.

Infant mortality rates in single, twin and triplet births, and influencing factors in Japan, 1995-98

The infant mortality rate (IMR) was analysed among single, twin and triplet births during the period from 1995 to 1998 using Japanese Vital Statistics. This study also investigated the effects of order of multiple births and of birthweight on the IMR. Proportions of neonatal deaths among total infant deaths were about 1/2 for singletons and 3/4 for both twins and triplets. Thus, to reduce the IMR, intensive care of multiple births is likely to be very important during the first month of life. The IMR was higher in males than females for both singletons and twins, but not in triplets. Relative risks of the IMR in multiples relative to singletons were 5-fold in twins and 12-fold in triplets. The IMR was higher in the second-born (18 per 1000 live births) than the first-born (16) twin and higher in the third-born (51) than the first-born (31) and the second-born (34) triplet. The higher risk in the second-born than the first-born twin may be related to delivery complications. The IMR decreased rapidly as birthweight increased in singletons, twins, and triplets. IMRs for < or =1500 g were 2.4 per 1000 live births in singletons, 5.9 in twins and 6.1 in triplets. The corresponding proportions of infant deaths were 75%, 33% and 10% respectively. The higher relative risks of multiple births are almost entirely the result of the lower birthweight distribution among twins and triplets. To reduce the IMR, birthweight is an important factor in twins, triplets and singletons. The overall early neonatal death rate decreased as gestational age rose in singletons, twins and triplets. For birthweights <1000 g, higher IMRs were related to gestational ages of <28 weeks.

Perinatal mortality in twins and factors influencing mortality in Japan, 1980--98

The perinatal mortality rate (PMR) in twins was analysed using Japanese vital statistics during the period 1980-98. There was a total of 1992 twin perinatal deaths. The PMR in twins significantly decreased from 91 per 1000 births in 1980 to 31 per 1000 in 1998. The PMR was higher in males than females, but the differences between the sexes decreased over time. It was significantly higher in the second-born than the first-born of the twins. The fetal death rate was 2.8 times higher in monozygotic than dizygotic twins. The PMR decreased to one-sixth for the maternal age group > or =40 years, one-fifth for <20 years, and between one-third and a half for 20--39 years during the period 1980--98. It was lowest for birthweights (BW) between 2500 g and 2999 g during the entire period; the PMR decreased with gestational age (GA) up to 38--39 weeks and increased thereafter. The effect of BW on the PMR was greater than that of GA except in the shorter GA group. The proportion of twin perinatal deaths with extremely low BW (<1000 g) increased from 50% in 1980 to 68% in 1998. Thus, the declining PMR was unlikely to be due to the improvement in BW in twins. It is likely that it is related to the improved medical management of twins during the perinatal period and the first week of life.