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Reproductive pattern among twins and singletons in relation to number of siblings: a Swedish cohort study of individuals born between 1973 and 1993
Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center of Paediatrics and Gynaecology and Obstetrics, Department of Gynaecology and Obstetrics in Linköping.
Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center of Paediatrics and Gynaecology and Obstetrics, Department of Gynaecology and Obstetrics in Linköping.
Linköping University, Department of Medical and Health Sciences, Division of Health Care Analysis. Linköping University, Faculty of Medicine and Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center of Paediatrics and Gynaecology and Obstetrics, Department of Paediatrics in Linköping.
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Background Twinning has been shown to be associated with a reduced reproductive rate compared to singletons. This can partly be explained by the birth-characteristics pertaining to twinning as many twins are born preterm, with low birth weight or small for gestational age. However, the intergenerational reproductive rate may also be due to familial factors such as number of siblings.

Methods This is a register-based study of all men and women born in Sweden between 1973 and 1993 who were living in Sweden at 13 years of age. Data on the study objects’ own births as well as their offspring, parental socio-demographic factors were collected from Swedish population based registers. Hazard ratios for the likelihood of becoming a parent were estimated using Cox’s proportion hazard models. All models were adjusted for socio-demographic and birth characteristics.

Results Adjusting for number of siblings, socio-demographic factors and birth characteristics, twinning was associated with a decreased likelihood of becoming a first-time parent, compared with singletons both for females (HR (95% CI)=0.90 (0.88-0.93) and males (HR (95% CI)=0.96 (0.93-0.99). Having 3 or more siblings increased the chance of becoming a first-time parent among both male twins (HR (95% CI)=1.17 (1.08-1.27)) and singletons (HR (95% CI)=1.16 (1.15-1.18)) compared to having fewer than 3 siblings. This increased likelihood of becoming a parent was also present among female twins (HR (95% CI)=1.18 (1.10-1.26)) and singletons (HR (95% CI)=1.22 (1.21-1.24)).

Conclusions Twins have a decreased likelihood of becoming a parent compared to singletons even when adjusting for number of siblings.

Place, publisher, year, edition, pages
2015.
Keyword [en]
Twinning, reproduction, siblings, prematurity, size for gestational age, birth weight
National Category
Pediatrics Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-121276OAI: oai:DiVA.org:liu-121276DiVA: diva2:853037
Available from: 2015-09-11 Created: 2015-09-11 Last updated: 2016-04-01Bibliographically approved
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 (print) (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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Division of Clinical SciencesFaculty of Medicine and Health SciencesDepartment of Gynaecology and Obstetrics in LinköpingDivision of Health Care AnalysisDepartment of Clinical and Experimental MedicineDepartment of Paediatrics in Linköping
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