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Reproductive patterns among twins: a Swedish register study of men and women born 1973-1983
Linköping University, Department of Clinical and Experimental Medicine, Obstetrics and gynecology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Obstetrics and gynecology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center of Paediatrics and Gynaecology and Obstetrics, Department of Gynaecology and Obstetrics in Linköping.
Linköping University, Department of Medical and Health Sciences, Health and Society. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Pediatrics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center of Paediatrics and Gynaecology and Obstetrics, Department of Paediatrics in Linköping.
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2013 (English)In: BMC Pregnancy and Childbirth, ISSN 1471-2393, E-ISSN 1471-2393, Vol. 13Article in journal (Refereed) Published
Abstract [en]

Background

During the last decades there has been a steady increase of twin births. A combination of improved medical treatment of preterm and small-for-gestational age children has contributed to a higher number of surviving twins. Prematurity is known to affect reproduction in a negative way. Few studies have focused on the potential effect twinning may have on future reproduction. Thus, the aim of this study was to investigate the effect of being born a twin compared to being born a singleton have on future reproduction.

Methods

In a national population-based register study, all individuals born between 1973–1983 who were alive and living in Sweden at 13 years of age (n = 1 016 908) constituted the sample. Data on each study subject’s own birth as well as the birth of their first offspring, and parental socio-demographic factors were collected from Swedish population based registers. Hazard ratios and corresponding 95% CI was calculated using Cox proportional hazards model.

Results

Twins, both men and women, had a reduced likelihood of reproducing compared to singletons (women: HR = 0.89, 95% CI = 0.86-0.93; men: HR = 0.92, 95% CI = 0.87-0.97). This difference in birth rates can only partly be explained by diverging birth characteristics. Amongst men and women born very preterm, twins had an increased likelihood of reproducing compared to singletons (women: HR = 1.25, 95% CI = 1.02-1.62; men: HR = 1.34, 95% CI = 1.01-1.78).

Conclusions

Twins have lower reproduction rates compared to singletons, which only to a certain degree can be explained by diverging birth characteristics.

Place, publisher, year, edition, pages
2013. Vol. 13
Keyword [en]
Twin, Singleton, Reproduction rate, Birth characteristics
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-89750DOI: 10.1186/1471-2393-13-6ISI: 000314290200001OAI: oai:DiVA.org:liu-89750DiVA: diva2:609360
Note

Funding Agencies|Medical Research Council of Southeast Sweden||

Available from: 2013-03-05 Created: 2013-03-05 Last updated: 2017-12-06
In thesis
1. Birth Characteristics’ Impacton Future Reproduction and Morbidity Among Twins an dSingletons
Open this publication in new window or tab >>Birth Characteristics’ Impacton Future Reproduction and Morbidity Among Twins an dSingletons
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Globally, in both developed and developing countries, the twinning rates have increased since the early 70’s. A large proportion of twins are born preterm and/or small-for-gestational-age (SGA) and/or with a low birth weight. Several studies have been performed on the long-term effect of these non-optimal birth characteristics on future reproductive performance and morbidity. Yet, most studies exclude twins or higher order pregnancies and thus the findings are based on singleton pregnancies only.

The aim of the present thesis was therefore to investigate the impact of non-optimal birth characteristics in terms of preterm birth, small-for-gestational age, and low birth weight, on the reproductive pattern and morbidity among twins and singletons Furthermore, the present thesis attempted to establish whether twins and singletons were affected in the same manner.

The studies included in this thesis are prospective population-based register studies, including all men and women, alive and living in Sweden at age 13, who were born between 1973 and 1983 (1,000,037 singletons and 16,561 twins) for the first three studies with follow-up till the end of 2006 and 2009. The last study included all men and women, alive and living in Sweden at age 13, who were born between 1973 and 1993 (2,051,479 singletons and 39,726 twins) with follow-up till the end of 2012.

In general, twins were found less likely to reproduce between 13 and 33 years of age compared with singletons. Stratifying data by different birth characteristics, it was found that twins had a lower likelihood of reproducing on several different birth characteristics (appropriate-for-gestational-age, normal birth weight, low birth weight, term birth, preterm birth). However, twins born very preterm had an increased likelihood of reproducing compared with singletons born very preterm.

Not taking birth characteristics into account, twinning was associated with a higher degree of hospitalization. However, accounting for the diverging birth characteristics this difference diminished and for some diagnoses the relationship was reversed such that twins were actually less likely to be hospitalized compared with singletons.

In terms of the heritability of non-optimal birth characteristics singleton mothers born preterm were more predisposed to give birth to a child that was preterm while singleton mothers born SGA more often gave birth to a child either born preterm or SGA. Among twins this heritability was not as evident. The only difference observed was among twin mothers born SGA who were more likely to give birth to a child born SGA.

In the extended cohort comprising those born between 1973 and 1993, male and female twins were found to be less likely to become parents compared with singletons. No difference was found among women in terms of having a second child, while male twins were more likely to have a second child compared with male singletons. It was also found that the likelihood of becoming a first-time parent and second-time parent was positively associated with the number of siblings.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 87 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1429
Keyword
Twin, singleton, preterm birth, SGA, reproduction, hospitalization, siblings
National Category
Pediatrics Health Sciences
Identifiers
urn:nbn:se:liu:diva-121279 (URN)10.3384/diss.diva-121279 (DOI)978-91-7685-961-2 (ISBN)
Public defence
2015-10-16, Berzeliussalen, Campus US, Linköping, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2015-09-11 Created: 2015-09-11 Last updated: 2016-04-01Bibliographically approved

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Bladh, MarieJosefsson, AnnCarstensen, JohnFinnström, OrvarSydsjö, Gunilla
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Obstetrics and gynecologyFaculty of Health SciencesDepartment of Gynaecology and Obstetrics in LinköpingHealth and SocietyPediatricsDepartment of Paediatrics in Linköping
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