Does
Frequent intercourses Prime the Immune System for Pregnancy?
For
decades, doctors have recommended that couples trying to conceive should have
intercourse as often as possible, not only during ovulation (obviously) but at
other times as well. Doing so is known to improve the odds of success, though
the reasons have remained a puzzle. Now two new studies suggest, somewhat
radically, that alters a woman’s immune system in ways that affect her chances
of conceiving.
The
data for the studies come from the Kinsey Institute for Research on this
matter, Gender and Reproduction and the Center for the Integrative Study of
Animal Behavior, both at Indiana University, where researchers recruited 30
healthy, premenopausal women, all of whom were hetero and not trying to become
pregnant. About half of them were intercourseually active, using condoms or
intrauterine devices as birth control, while the others were abstinent. The
volunteers provided blood, saliva and other samples throughout several
menstrual cycles. Apart from their own lives, women in both groups were broadly
similar in terms of health and lifestyle.
They
soon revealed distinctly different immune-system responses over the course of a
menstrual cycle. According to one of the new studies, published in September in
the journal Fertility and Sterility, the active women displayed
heightened levels of a certain immune cell when their reproductive systems were
preparing to release an egg but before they were able to become pregnant. Later
in the menstrual cycle, when conception was possible, these women developed
higher levels of a different type of immune cell — one known to help a body
recognize and ignore nonhazardous foreign cells, like those in a fetus. There
were no similar changes in the immune systems of the abstinent women.
The
other study, published in Physiology and Behavior, found other immunological
differences. active women early in their cycles developed more antibodies
of a type that lives in the mucus lining the reproductive tract and represents
a threat to sperm and fetuses. Levels of these antibodies dropped later in the
cycle, while the numbers of a different germ-fighting antibody in the blood but
not in the reproductive tract grew.
Together,
these findings indicate that ‘‘the more frequently a woman engages in such
activity, the more often her immune system gets the message that it’s time to
reproduce,’’ says Tierney Lorenz, the research scientist at the Kinsey
Institute who was the lead author of both studies. The research did not examine
conception or rates of illness and infection, so the real-life implications of
the differences in immunity remain uncertain. It’s also not clear how the
immune system knows someone is having it. There may be messages from the brain
or extra changes in hormones, Lorenz says. partners may even exchange
elements of their microbiome, prompting changes in each other’s immunity. For
now, the primary lesson Lorenz takes away from these studies, she says, is
‘‘awe for the elegance of our flexible, powerful, socially aware immune
system.’’
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