Reproductive pattern among twins and singletons in relation to number of siblings : a Swedish cohort study of individuals born between 1973 and 1993

• 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.

Subject headings

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Pediatrik (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Pediatrics (hsv//eng)

MEDICIN OCH HÄLSOVETENSKAP  -- Hälsovetenskap (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Health Sciences (hsv//eng)

Keyword

Twinning

reproduction

siblings

prematurity

size for gestational age

birth weight

Publication and Content Type

vet (subject category)

ovr (subject category)