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prior discussion regarding the unity of body and soul. The scientific study of the biological signs
involved in procreation has enjoyed a surge of research efforts within the last fifty years since the
promulgation of Humanae Vitae. However, the encyclical situates the discoveries of
reproductive science—both practically and morally—within the context of responsible
parenthood, stating unequivocally that “with regard to the biological processes, responsible
parenthood means an awareness of, and respect for, their proper functions.” 106 St. John Paul II
asserts that modern research regarding the physiological dimensions of human fertility has much
to offer a theological study of marriage and the family. 107 However, he cautions that scientific
pursuits in this field must be grounded in a proper respect for the spousal mystery as it pertains to
personal dignity, human fulfilment, and the moral order.
Although scientists differ in methods, analyses, and calculations in the evaluation of a
woman’s “fertile window” 108 and the timing of ovulation, the most valid means of self-
identification involves the observation of cervical mucus, readily collected at the opening of the
vagina. 109 As a woman progresses through the different phases of the menstrual cycle, changes in
the cervical mucous indicate approaching ovulation. Mucous observations made during this
fertile interval, although varying among women and across cycles, typically include the day of
ovulation and several days leading up to it. 110 Ovulation is usually marked by a specific type of
mucus, which is transparent in appearance, slippery or lubricative, and stretchy, with the most
106
HV, sec. 10.
John Paul II, “Marriage in the Integral Vision of Man,” para. 6, 9.
108
Jamie L. Bigelow et al., “Mucus Observations in the Fertile Window: A Better Predictor of Conception
than Timing of Intercourse,” Human Reproduction 19, no. 4 (April 2004): 889-892, accessed May 27, 2018,
http://dx.doi.org/10.1093/humrep/deh173.
107
109
Martin Owen, “Physiological Signs of Ovulation and Fertility Readily Observable by Women,” The
Linacre Quarterly 80, no. 1 (2013): 17-23, accessed May 27, 2018,
http://dx.doi.org/10.1179/0024363912Z.0000000005.
110
Bigelow et al., “Mucus Observations,” 889-892.