It seems a no-brainer for women trying to conceive: You’re more likely to
get pregnant when you have more sex.
But while experts have known that women who have sex throughout their
cycle have a better chance of conceiving, they haven’t been able to pinpoint
why — until now.
Two new studies from Indiana University published in the journalsFertility
and Sterility and Physiology & Behavior studied
menstrual cycle data from 30 women and determined that having sex throughout a
woman’s cycle — even when she’s not ovulating — creates physiological changes
that increase her odds of getting pregnant.
Researchers found that women who are sexually active have bigger changes
in helper T cells (which manage the body’s immune response) as well as the
proteins that helper T cells use to communicate.
Among the findings: There were significantly higher levels of type 2
helper T cells (which help a woman’s body accept sperm and an embryo) in women
who were sexually active during the luteal phase of their menstrual cycle, i.e.
the period in which the uterine lining thickens in anticipation of pregnancy.
Researchers also discovered that sexually active women had higher levels
of immunoglobulin G antibodies (which fight disease without interfering with
the uterus) during the luteal phase.
As a result, they determined that the bodies of women who have sex
throughout their cycle may be better at fighting off illness while
simultaneously welcoming sperm or a fetus at the right moment.
Researchers didn’t detect these immunity changes in women who abstained
from sex.
Lead study author Tierney Lorenz, PhD, a visiting research scientist at
The Kinsey Institute, tells Yahoo Health that they’re not exactly sure why this
immune response happens, but she has several theories.
One is that sex might trigger changes in hormone patterns across a
woman’s menstrual cycle or change her rates of ovulation. As a result, a
woman’s autonomic nervous system may act differently over the course of
her menstrual cycle.
There may also be a link between exposure to bacteria from a woman’s
partner and increased fertility. “Getting exposed to your intimate partner’s
microbiome (the combination of bacteria, yeasts, and other very tiny organisms
that live inside and on all of us) might challenge the immune system in ways
that are different than if it were not exposed to that microbiome,” Lorenz
says.
A man’s ejaculate may also stimulate or suppress the immune response in a
woman’s reproductive tract or send a signal to the rest of her immune system to
change in some important ways, she says.
But Lorenz also says there may be some other factor they’re just not
aware of yet, such as a difference in diet, sleep, or social interactions among
women who are and aren’t having sex.
So, what does all of this mean for women trying to conceive?
While Lorenz’s research found that the more frequently a woman has sex,
the more often her immune system “gets the message that it’s time to
reproduce,” she also points out that even a single act of sex that happens
outside of a woman’s “fertile window” is still useful for increasing her
fertility.
Her advice: “Do what works right in your relationship.”
Korin
Miller
