Offspring number, pregnancy, and risk of a first clinical demyelinating event: The AusImmune Study

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Abstract

Objective:

To examine the association between past pregnancy, offspring number, and first clinical demyelination risk.

Methods:

Cases (n = 282) were aged 18–59 years with a first clinical diagnosis of CNS demyelination (first clinical demyelinating event [FCD]) and resident within 1 of 4 Australian centers (from latitudes 27° south to 43° south) from 2003 to 2006. Controls (n = 542) were matched to cases on age, sex, and study region, without first clinical diagnosis of CNS demyelination.

Results:

Higher offspring number was associated with FCD risk among women (p < 0.001) but not men (p = 0.71); difference in effect; p = 0.001. Among women, higher parity was associated with reduced risk of FCD (adjusted odds ratio 0.51 [95% confidence interval 0.36, 0.72] per birth) with a similar magnitude of effect observed among classic first demyelinating events (adjusted odds ratio 0.47 [95% confidence interval 0.29, 0.74]). The apparent beneficial effect of higher parity was also evident among parous women only (p < 0.001). Among cases, a clear female excess was evident for those with low but not high (4 or more) offspring number. Factors such as human leukocyte antigen DR15 genotype did not appear to modify the association between higher parity and a reduced FCD risk among women.

Conclusions:

These findings are consistent with a cumulative beneficial effect of pregnancy. Temporal changes toward an older maternal age of parturition and reduced offspring number may partly underlie the increasing female excess among MS cases over time.

GLOSSARY

AOR: adjusted odds ratio

GLOSSARY

CI: confidence interval

GLOSSARY

EAE: experimental allergic encephalomyelitis

GLOSSARY

EBNA: Epstein-Barr virus nuclear antigen

GLOSSARY

EBV: Epstein-Barr virus

GLOSSARY

FCD: first clinical demyelinating event

GLOSSARY

FDE: first demyelinating event

GLOSSARY

HLA: human leukocyte antigen

GLOSSARY

IgG: immunoglobulin G

GLOSSARY

MS: multiple sclerosis

GLOSSARY

OR: odds ratio

GLOSSARY

RA: rheumatoid arthritis

GLOSSARY

VCA: viral capsid antigen.

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