Fecundity and twinning. A study within the Danish National Birth Cohort
Open Access
- 1 October 2004
- journal article
- research article
- Published by Oxford University Press (OUP) in Human Reproduction
- Vol. 19 (10), 2222-2226
- https://doi.org/10.1093/humrep/deh437
Abstract
BACKGROUND. Decreased fecundity has been hypothesized as one of the causes of the widespread decline in twin rates in the 1960s and 1970s. The association between high fecundity and twinning is not, however, well documented. METHODS. In the Danish National Birth Cohort, we identified 56 295 births (including 729 twin deliveries) with data on pregnancy planning and time to pregnancy (TTP) and no report of infertility treatment. We estimated the odds ratio (OR) of twinning as a function of TTP and having planned a pregnancy. RESULTS. Increasing TTP correlated with decreased twinning rates. Compared with women who conceived within 2 months of trying, women who took longer than 1 year had an OR of 0.55 (95% confidence interval 0.39–0.77) of giving birth to twins. The association was slightly stronger for opposite sex twins. Women not planning a pregnancy had a lower rate of opposite sex twins than planners, but a comparable rate of same sex twins. We saw an excess of same sex pairs in women conceiving despite contraception. CONCLUSIONS. A long TTP is associated with a reduced risk of twinning. The marked decline observed in the 1960s and 1970s may derive from a widespread decrease in fecundity.Keywords
This publication has 14 references indexed in Scilit:
- TwinningThe Lancet, 2003
- A COMPARATIVE STUDY OF ZYGOTIC TWINNING AND TRIPLET RATES IN EIGHT COUNTRIES, 1972–1999Journal of Biosocial Science, 2003
- Changes in twinning rate: Italy 1950-1996Human Reproduction, 2003
- The Danish National Birth Cohort - its background, structure and aimScandinavian Journal of Public Health, 2001
- The use of twinning rates as a reproductive health monitor in England and Wales 1988-1996.Human Reproduction, 1998
- Population based study of rates of multiple pregnancies in denmark, 1980-94BMJ, 1997
- Recent secular trends in dizygotic twinning rates in EuropeJournal of Biosocial Science, 1986
- Second survey Of secular trends in twinning ratesJournal of Biosocial Science, 1982
- Twinning in Relation to the Marital Status of the MotherHuman Heredity, 1967
- THE EFFECT OF PARENTAL AGE, PARITY AND DURATION OF MARRIAGE ON THE TWINNING RATEAnnals of Human Genetics, 1959