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Birth Characteristics’ Impacton Future Reproduction and Morbidity Among Twins an dSingletons
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.
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 [en]
Twin, singleton, preterm birth, SGA, reproduction, hospitalization, siblings
National Category
Pediatrics Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-121279DOI: 10.3384/diss.diva-121279ISBN: 978-91-7685-961-2 (print)OAI: oai:DiVA.org:liu-121279DiVA: diva2:853070
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
List of papers
1. Reproductive patterns among twins: a Swedish register study of men and women born 1973-1983
Open this publication in new window or tab >>Reproductive patterns among twins: a Swedish register study of men and women born 1973-1983
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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.

Keyword
Twin, Singleton, Reproduction rate, Birth characteristics
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-89750 (URN)10.1186/1471-2393-13-6 (DOI)000314290200001 ()
Note

Funding Agencies|Medical Research Council of Southeast Sweden||

Available from: 2013-03-05 Created: 2013-03-05 Last updated: 2017-12-06
2. Hospitalization in Adolescence and Young Adulthood Among Twins and Singletons: A Swedish Cohort Study of Subjects Born Between 1973 and 1983
Open this publication in new window or tab >>Hospitalization in Adolescence and Young Adulthood Among Twins and Singletons: A Swedish Cohort Study of Subjects Born Between 1973 and 1983
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2013 (English)In: Twin Research and Human Genetics, ISSN 1832-4274, E-ISSN 1839-2628, Vol. 16, no 3, 707-715 p.Article in journal (Refereed) Published
Abstract [en]

Children born with non-optimal birth characteristics — that is, are small for gestational age and/or preterm — have an increased risk for several long-term effects such as neurological sequelae and chronic disease. The purpose of this study was to examine whether twins exhibited a different outcome, compared with singletons, in terms of hospitalization during adolescence and early adulthood, and to what extent differences remain when considering the divergence in birth characteristics between singletons and twins. Persons born between 1973 and 1983 in Sweden and surviving until age 13 were included and followed until the end of 2006. Data on birth characteristics, parental socio-demographic factors, and hospitalizations were collected from national registers. Adjusting for parental socio-demographic factors, twins had a higher risk of being hospitalized than singletons (odds ratio, OR = 1.17, 95% confidence interval, CI = 1.10–1.25) and more often due to ‘Congenital anomalies’ (OR = 1.18, 95% CI = 1.06–1.28), ‘Infections’ (OR = 1.14; 95% CI = 1.08–1.20), ‘External causes of illness’ (OR = 1.10, 95% CI = 1.06–1.15), and ‘Diseases of the nervous system’ (OR = 1.18, 95% CI = 1.10–1.26). Stratifying for birth characteristics, this difference diminishes, and for some diagnoses non-optimal twins seem to do slightly better than non-optimal singletons. Thus, twins with non-optimal birth characteristics had a lower risk of hospitalization than non-optimal singletons on, for example, ‘Congenital anomalies’ and ‘Diseases of the nervous system’ (OR = 0.86, 95% CI = 0.77–0.96; OR = 0.88, 95% CI = 0.81–0.97, respectively) and Total (any) hospitalization (OR = 0.87, 95% CI = 0.83–0.92). Among those with optimal birth characteristics, twins had an increased hospitalization due to ‘External causes of illness’ (OR = 1.07, 95% CI = 1.02–1.13) compared with optimal singletons. Twins have higher hospitalization rates than singletons. In stratifying for birth characteristics, this difference diminishes, and for some diagnoses, non-optimal twins seem to do less poorly than non-optimal singletons.

Place, publisher, year, edition, pages
Cambridge University Press (CUP), 2013
Keyword
twin, singleton, morbidity, SGA, preterm, low birthweight
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-94317 (URN)10.1017/thg.2013.27 (DOI)000319127400007 ()
Available from: 2013-06-24 Created: 2013-06-24 Last updated: 2017-12-06
3. Intergenerational cohort study of preterm and small-for-gestational-age birth in twins and singletons
Open this publication in new window or tab >>Intergenerational cohort study of preterm and small-for-gestational-age birth in twins and singletons
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2015 (English)In: Twin Research and Human Genetics, ISSN 1832-4274, E-ISSN 1839-2628, Vol. 18, no 5, 581-590 p.Article in journal (Refereed) Published
Abstract [en]

To date several studies have investigated the intergenerational effect of preterm and small-for-gestational-age births. However, most studies excluded both twin mothers and twin offspring from the analyses. Thus, the objective of this study was to investigate the intergenerational effect of preterm birth and small for gestational age (SGA) among twins and singletons.

A prospective population based register study of mother-first-born offspring pairs recorded in the Swedish Medical Birth Register was performed. The study included 4073 twins and 264,794 singletons born in 1973-1983 and their firstborns born in 1986-2009. Preterm birth was defined as birth <37 weeks of gestation and SGA as < 2 standard deviations of the Swedish standard. Logistic regressions were performed to estimate the intergenerational effect of each birth characteristic. Adjustments were made for maternal grandmothers and mother’s socio-demographic factors in addition to maternal birth- characteristics.

Among mothers born as singletons, being born preterm was associated with an increased risk for delivering a preterm child (adjusted OR 1.39, 95% CI 1.29-1.50) while being born SGA increased the likelihood of a SGA child (adjusted OR 3.04, 95% CI 2.80-3.30) as well as a preterm child (adjusted OR 1.30, 95% CI 1.20-1.40). In twin mothers, the corresponding ORs tended to be lower and the only statistically significant association was between a SGA mother and a SGA child (adjusted OR 2.15, 95% CI 1.40-3.31). A statistically significant interaction between twinning and mother’s size for gestational was identified in a multivariate linear regression analysis indicating that singleton mothers born SGA were associated with a lower birth weight compared to mothers not born SGA.

Preterm birth and SGA appear to be transferred from one generation to the next, although not always reaching statistical significance. These effects seem to be less evident in mothers born as twins compared with those born as singletons.

Place, publisher, year, edition, pages
Cambridge University Press, 2015
National Category
Pediatrics Health Sciences
Identifiers
urn:nbn:se:liu:diva-121275 (URN)10.1017/thg.2015.60 (DOI)000361660800010 ()
Note

Funding: Medical Research Council of Southeast Sweden

Available from: 2015-09-11 Created: 2015-09-11 Last updated: 2017-12-04Bibliographically approved
4. Reproductive pattern among twins and singletons in relation to number of siblings: a Swedish cohort study of individuals born between 1973 and 1993
Open this publication in new window or tab >>Reproductive pattern among twins and singletons in relation to number of siblings: a Swedish cohort study of individuals born between 1973 and 1993
Show others...
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.

Keyword
Twinning, reproduction, siblings, prematurity, size for gestational age, birth weight
National Category
Pediatrics Health Sciences
Identifiers
urn:nbn:se:liu:diva-121276 (URN)
Available from: 2015-09-11 Created: 2015-09-11 Last updated: 2016-04-01Bibliographically approved

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