The estimated risk of miscarriage should be corrected for induced abortion rates.
OBJECTIVE
We wanted to study to what extent induced abortion rates influence the age-dependent estimates of miscarriage risk.


METHODS
Register-based study.


METHODS
Linkage between hospital records and the Norwegian Population Registry.


METHODS
Included were all women 15-49 years of age in Oslo, Norway, who were pregnant during the three-year study period, 27,932 women.


METHODS
We estimated proportions with miscarriage according to maternal age with and without inclusion of women with induced abortion in the denominator.


METHODS
Proportions with miscarriage in each age group and odds ratios of miscarriage, with age group 25-29 years as the reference.


RESULTS
When only women with pregnancies intended to term were included in the denominator, 9.4% of the women were estimated to have miscarriage as the only reproductive event during the three-year period and 6.8% had both miscarriage and delivery. The corresponding figures when also women with induced abortions were included in the denominator, were 7.0 and 5.0%. When taking induced abortion into account, the reduction in estimated proportion with miscarriage during the study period was greatest in the age groups with the highest induced abortion rates, women 15-19 years old (from 22.8 to 6.4%) and women 45-49 years old (from 57.9 to 41.0%).


CONCLUSIONS
Estimates of age-dependent risk of miscarriage may be strongly influenced by induced abortion rates.
Eskild
Anne
A
Department of Obstetrics and Gynaecology, Akershus University Hospital and Medical Faculty, University of Oslo, Lørenskog, Norway. anne.eskild@medisin.uio.no
Vatten
Lars J
LJ
Nesheim
Britt-Ingjerd
BI
Vangen
Siri
S
D000028:Abortion, Induced / Q000009:adverse effects* / Q000706:statistics & numerical data*; D000022:Abortion, Spontaneous / Q000453:epidemiology* / Q000209:etiology*; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D005260:Female; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D016017:Odds Ratio; D011247:Pregnancy; D012042:Registries; D012307:Risk Factors; D055815:Young Adult