30
In general, when a woman is fertile the cervix is open, whereas it is closed during infertile
periods within the menstrual cycle. 118 The authors of one recent study refer to the cervix as “the
door to the female reproductive system.” 119 Indeed, it functions primarily as a protection against
infection of the upper reproductive tract, but it also facilitates the penetration of sperm through
the uterus and fallopian tubes when ovulation is imminent. 120
While the cervix functions as a gatekeeper anatomically, 121 there is also a more intricate
series of events acting as a “biological valve” at a cellular level within the cervical canal. 122
Microscopic studies of fertile cervical mucus reveal fern-like patterns or channels within the
mucus itself. 123 These parallel strands aid the movement of sperm through the vagina and cervix
and into the upper reproductive tract where fertilization occurs. The strands function as a
pathway through which sperm travel towards the waiting ovum. During the infertile phases or
when a woman observes dry days, there is a marked reduction in sperm channels and the
biological valve closes, along with the cervical opening itself. 124 In fact, when ovulation is not
imminent or has passed, the mucus presents a barrier to sperm penetration. 125 Fertile cervical
118
Martyn, McAuliffe, and Wingfield, “The Role of the Cervix,” 2092-2098.
Ibid.
120
Ibid.
121
Ibid.
122
Thomas W. Hilgers, The NaPro Technology Revolution: Unleashing the Power in a Woman’s Cycle
(New York, Beaufort, 2010), 7.
123
Menárguez, Pastor, and Odeblad, “Morphological Characterization,” 1782-1789.
124
Thomas W. Hilgers and Ann M. Prebil, “The Ovulation Method—Vulvar Observations as an Index of
Fertility/Infertility,” Obstetrics and Gynecology 53, no. 1 (1979): 12-22, quoted in Thomas W. Hilgers, The NaPro
Technology Revolution: Unleashing the Power in a Woman’s Cycle (New York, Beaufort, 2010), 7.
125
Erik Odeblad, “The Discovery of Different Types of Cervical Mucus and the Billings Ovulation
Method,” Bulletin of the Ovulation Method Research and Reference Centre of Australia 21, no. 3 (1994): 3035,
accessed May 27, 2018, https://www.woombinternational.org/index.php/science-of-fertility/item/49-the-discovery-
of-different-types-of-cervical-mucus-and-the-billings-ovulation-method.
119