Time trends in human fecundability in Sweden.
BACKGROUND
Trends in biologic fertility are elusive. Possible negative trends in male reproductive health are still debated, and their effect on human fertility might be negligible. Time-to-pregnancy (TTP) is a functional measure of couple fecundability.


METHODS
We analyzed data on TTP among 832,000 primiparous women 20 years of age and older in the nationwide Swedish Medical Birth Registry from 1983 through 2002. This age restriction led to an exclusion of 10% of primiparous pregnancies. Subfertility (TTP > or =1 year) was analyzed as a function of maternal age, calendar time at initiation of attempt, and birth cohort-taking into account the truncation problems that are inherent in birth-based retrospective sampling.


RESULTS
Subfertility generally decreased over successive birth cohorts. When studied as a period effect, a transient increase in subfertility was seen in the early 1990s. Subfertility increased with age, except that for women in their late 1930s, an apparent decrease was observed, particularly among the early cohorts.


CONCLUSIONS
We found decreasing subfertility over time. We speculate that these patterns might be related to a Sweden-specific decrease over time in sexually transmitted diseases, to changes in sexual behavior induced by socioeconomic conditions, or to broader biologic or educational trends.
Scheike
Thomas H
TH
Department of Biostatistics, University of Copenhagen, Denmark. T.Scheike@biostat.ku.dk
Rylander
Lars
L
Carstensen
Lisbeth
L
Keiding
Niels
N
Jensen
Tina Kold
TK
Stromberg
Ulf
U
Joffe
Michael
M
Akre
Olof
O
D000328:Adult; D000367:Age Factors; D015988:Cohort Effect; D003710:Demography; D005260:Female; D005298:Fertility; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D018873:Pregnancy Rate / Q000639:trends*; D012042:Registries; D012044:Regression Analysis; D013548:Sweden; D013997:Time Factors