Trends in multiple births in Italy: 1955-1983

Trends in Dizygotic and Monozygotic Spontaneous Twin Births During the Period 2007-2017 in Lombardy, Northern Italy: A Population-Based Study

In this study, we analyzed the estimated frequency of monozygotic (MZ) and dizygotic (DZ) spontaneous twins in Lombardy during the period 2007-2017. This is a population-based study using the regional healthcare utilization databases of the Lombardy Region. The total number of spontaneous twin deliveries, in separate strata of like and unlike sex, was obtained. Moreover, estimates of DZ and MZ twin births were calculated using Weinberg's method. The standardized rates (SRs), adjusted for maternal age, of DZ and MZ twin births were computed according to calendar period. The twinning rates were calculated among strata of parity and maternal age. Finally, DZ:MZ ratio was calculated. Among the 734,278 spontaneous deliveries, 9176 (12.5 out of 1000 births) couples of twins were identified. In the three periods considered (i.e. 2007-2010, 2011-2014 and 2015-2017), no trend in the SRs of MZ twins was observed, respectively 0.41 (95% CI [0.40, 0.43]), 0.43 (95% CI [0.42, 0.45]) and 0.43 (95% CI[0.42, 0.45]). Differently, a slightly decreasing trend was observed in DZ twins SRs, respectively 0.87 (95% CI [0.84, 0.89]), 0.81 (95% CI [0.79, 0.83]), and 0.78 (95% CI [0.76, 0.80]). As concerns parity and maternal age, the rate of DZ twin births was consistently higher in nulliparae women aged 35 years or more. In our cohort, despite the increase of maternal age, a decline of spontaneous twin births emerged, especially due to the downward trend of DZ twins.

Time trends in biological fertility in Western Europe

We investigated trends in biological fertility in a comprehensive analysis of 5 major European data sets with data on time to pregnancy (TTP) and proportion of contraceptive failures. In particular, we distinguished a period effect from a birth cohort effect (lifelong tendency) in both sexes. Attempts at conception not resulting in birth were excluded. We analyzed data on pregnancies occurring in 9,247 couples between 1953 and 1993 and performed sensitivity analyses to check the robustness of findings. Separate analyses of each time effect showed an increasing fertility trend. Mutually adjusted analyses demonstrated that this rise was visible as a male cohort effect for both TTP and contraceptive failure. On the other hand, the female birth cohort effect showed a slight fall in the first half of the study period for both TTP and contraceptive failure. As a period effect, fertility remained generally stable, the slight trends in TTP and contraceptive failure being in opposite directions, likely indicating an artifact. The rising trend accords with most previous evidence. The increasing trend in male fertility does not contradict the previously reported semen quality deterioration, the effects of which are calculated to be small. The declining female fertility accords with a falling dizygotic twinning rate during the same period.

A Study of Multiple Deliveries in Portugal: Indications of an Iberian Peninsula Pattern

Information on multiple deliveries with regard to Portugal is scarce. Based on data provided by the Portuguese Institute of Statistics (INE), the rates for double and triple deliveries were calculated since 1930. The results obtained show for twins a uniform temporal pattern up to the 1970s. At this time rates decreased, but later they gradually recovered, reaching their maximum level in 2010. For triplets, the highest rates occurred between 1999 and 2002. For the period 1988–2011, the rates of multiple deliveries were related to a set of variables recorded in the INE database on live births. Significant differences (p < .001) between simple and multiple deliveries were obtained for maternal age, parity and marital status. Considering the year when the delivery occurred, significant differences (p < .001) persisted for maternal age regardless of the year. For the type of mating, significance was consistently found since the year 2002 (either by using the marital or the cohabitation criteria), and for parity since 2003. With regard to territorial variation, throughout seven periods between 1930 and 2011, the rates among the 20 administrative Portuguese territories, including the two insular districts of Açores and Madeira, were mostly stable for twinning rates, with a minimum level in 1970–1989. Regarding triplets, the greatest inter-district variation was found after 1980. The results of the Portuguese study on multiple deliveries are interpreted in the context of the Iberian Peninsula based on findings reported for Spain.

Temporal and Territorial Analysis of Multiple Deliveries in Spain (1900–2006)

Temporal variations in the frequency of multiple maternities in many Western European countries have been described. However, within a single country, regional differences are observed. Urban industrialized regions and rural agricultural areas have experienced in recent decades a distinct decline in multiple deliveries, which in cases have been related to maternal age and parity changes. Research on multiple deliveries in Spain is scarce and none of the studies go back to the beginning of the 20th century or consider regional variation over an extended period of time. The present paper is a yearly study on multiple deliveries in Spain since 1900 including a geographical analysis. Rather than dealing with recent changes in multi-parity, this paper is concerned with Spain's long-term national variation (between 1900 and 2006). The changing pattern of double and triple deliveries was analyzed using data from the Spanish National Statistics Institute (INE). Twinning rates in Spain are low in comparison to those of equivalent periods in other countries, and the minimum rates correspond to the 1980s decade. Results were interpreted by taking into account the influence of age at maternity and reproductive variation up to 1990. A good fit between observed and predicted rates was obtained after the application of models, which besides maternal age and parity, include their interaction. Regarding territorial variability, the values corresponding to southern, northern and insular Spanish provinces are consistent with an earlier reduction of the crude birth rate in the north-east regions and latter in the southern regions and the Canary Islands.

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.

Factors Associated with Recent Increase of Multiple Births in Spain

The increased incidence of multiple deliveries in Spain, in addition to changes in age at maternity and parity, is attributed to assisted reproductive treatments, but the relative contribution of the latter to this rise remains uncertain, due to the scarce information provided by clinics practicing those treatments. Population based data (1984–2004), including information on mother's age, nationality, marital status, date of delivery, and the characteristics of each (parity, single or multiple), and sex of newborns were provided by the Spanish Institute of Statistics. Twinning and triplet deliveries relate to maternal age, parity, and nationality. For younger ages (≤ 19, 20–24, 25–29) rates remained constant over time, but for older women (30–34, 35–39, ≥ 40) rates increased after 1994. From 1984 to 2004 the percentage of twins of opposite sex increased from 24.31 to 36.58 per cent. Since 1997, Spanish and non-Spanish mothers differentiate with respect to multiple maternity at ages over 30. In addition to unmarried Spanish women, immigrants constitute a reliable reference group that determines the convenience of segregating information on multiple deliveries respecting origin. The proportion of twins and triplets of opposite sex, maternal age, and parity patterns observed are concordant with a differential access to reproductive treatments depending on the woman's age. The present norm regulating the maximum number of fertilizations per cycle and the demand for these treatments explain the high incidence of multiple deliveries in Spain. A modified logistic curve predicts a stabilization of multiple deliveries, which will probably continue to be high in Spain.

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.

Does assisted hatching pose a risk for monozygotic twinning in pregnancies conceived through in vitro fertilization?

OBJECTIVE

To examine the association between assisted hatching and monozygotic (MZ) twinning.

DESIGN

Case-control.

SETTING

Population-based sample of IVF-ET cycles initiated in U.S. clinics, 1996.

PATIENT(S)

The IVF-ET (n = 35,503) cycles and 11,247 resultant pregnancies.

INTERVENTION(S)

Use of an assisted hatching procedure on embryos transferred.

MAIN OUTCOME MEASURE(S)

Cases were pregnancies for which number of fetal hearts observed on ultrasound exceeded number of embryos transferred. These pregnancies were considered to contain at least one MZ set of twins. Cases were compared with two control groups: other multiple-gestation pregnancies (>/=2 fetal hearts but number of fetal hearts </= number of embryos transferred); and singleton pregnancies (1 fetal heart).

RESULT(S)

Women with a case pregnancy were more likely to have received embryos treated with assisted hatching procedures than were women in either control group. After adjustment for patient age, number of embryos transferred, prior cycles, infertility diagnosis, intracytoplasmic sperm injection, and whether embryos from the current cycle were cryopreserved for later use, odds ratios and 95% CIs for use of assisted hatching were 3.2 (1.2-8.0), compared with other multiple-gestation pregnancies, and 3.8 (1.8-9.8), compared with singleton pregnancies.

CONCLUSION(S)

Assisted hatching may pose a risk for MZ twinning.

Recent trends in the incidence of multiple births and associated mortality in England and Wales

AIM

To review trends in multiple births and associated mortality in England and Wales since 1975, in the light of trends for earlier years; to assess, within the limitations of the available data, the extent of any association between multiple birth rates and assisted conception and drugs used for subfertility.

METHODS

Data collected routinely in England and Wales, between 1975 and 1994, were retrospectively reviewed. These comprised Office of Population Censuses and Surveys (OPCS) data collected at the registration of live and stillbirths and deaths occurring under the age of 1 year in England and Wales from 1975 onwards. Department of Health data about NHS prescriptions dispensed outside hospitals within England for drugs which could be used in the medical management of subfertility were also included.

RESULTS

The proportion of pregnancies that resulted in a registered multiple birth increased from a low of 9.9 per thousand in 1975 to 13.6 per thousand in 1994. Up to 1992, the increase was seen in all age groups except for women under 20, with the most substantial increase being in women aged 35 to 39. The rise in the rate of triplet and other higher order births was much steeper than that for all multiple births, increasing from 0.13 sets of triplets per thousand maternities in 1975, to 0.41 in 1994. Prescriptions dispensed for selected drugs that may be used for the medical management of subfertility and assisted conception became more common over this period. The fragmented nature of the data precluded direct comparison with changes in multiple birth rates, however.

CONCLUSIONS

Although the causes of the rise since 1980 in multiple birth rates in general, and the dramatic rise in the triplet rate in particular, cannot be ascertained or quantified directly from routinely collected data, drugs used for subfertility and more recently, assisted conception, probably had a major role.

What proportion of multiple births are due to ovulation induction? A register-based study in Italy

OBJECTIVES

This study evaluated the increase in risk of multiple births associated with ovulation induction and calculated the proportion of multiple births attributable to this treatment.

METHODS

Cases were 350 multiple births and controls were 737 single births enrolled from April 1993 to March 1994 in the Mercurio Project, an investigation of reproductive outcomes in Italy.

RESULTS

Ovulation induction was used in 45 case births (12.9%) and 24 control births (3.3%); the adjusted odds ratio was 4.1 (95% confidence interval [CI] = 2.4, 6.9). The odds ratio for triplet or higher order births was 72.2 (95% CI = 25.7, 202.8). When unlike-sexed multiple births were considered, the odds ratio increased for twin births, but not for triplet or higher births. The highest odds ratios were found when ovulation induction was used with assisted reproduction. The proportion of multiple births attributable to ovulation induction was 9.7% overall, 5.4% for twin births, and 69.8% for triplet or higher births.

CONCLUSIONS

Ovulation induction increases the risk of multiple births and has been responsible for the rise in the rate of triplet or higher order births in Italy in the last decade. Its indiscriminate and improper use should be avoided.

The epidemiology of multiple pregnancies

Over the last decades the frequency of multiple births has been on the decline in most developed countries. This trend, however, has been restricted to dizygotic twins, while monozygotic rates have remained stable or risen slowly. In more recent years, however, the fall in multiple dizygotic birth rates has ceased and a slight increase is observed. This trend and the increased frequency of triplets or higher-order births, registered from the early 1980s onwards, are essentially related to treatments for infertility. No single risk factor, such as maternal age, parity, oral contraceptive use, or declining fertility rates can explain the overall declining trends. In this paper we review the descriptive epidemiology and the main risk factors for multiple pregnancies.

Trends in multiple deliveries and infertility treatments in France

OBJECTIVE

To point out the association between infertility treatments and the increasing number of multiple deliveries.

DESIGN

Comparison over time of the incidence of multiple deliveries, the proportion of deliveries resulting from assisted conception (AC), and ovulation inductor sales.

DATA

Use of existing statistics: vital statistics, surveys of AC centres and ovulation inductor sales.

RESULTS

Between 1972 and 1989 the incidence of twin deliveries rose from 8.8/1000 to 11.2/1000, and the incidence of triplet deliveries from 0.9/10,000 to 4.4/10,000. This upward trend was particularly remarkable among women aged 30 to 39. Since 1978, the triplet delivery rates and the sales of Human Menopausal Gonadotrophin have been rising similarly. Between 1985 and 1989, 26 per cent of the triplet deliveries followed assisted conception and nearly 50 per cent were estimated to be due to ovulation inductor agents.

CONCLUSIONS

The results suggest a strong influence of infertility treatments and especially ovulation inductor agents in the dramatic increase of triplet deliveries.