Defining that short window that the ovulated egg is available to receive the sperm (12-24 hours) is imperative. However, the physical discomfort (Mittleschermz) that is associated with ovulation is experienced by surprisingly few women. Moreover, less than one-third of regularly cycling, highly-motivated women accurately can predict ovulation without formal monitoring.
Basal body temperature monitoring is an inexpensive and simple, although time-intensive method of observation. Upon ovulation, progesterone hormone increases. Progesterone causes a modest increase in basal body temperature (0.5F-1F) which is sustained throughout the second stage of the menstrual cycle. In a normal, cycling woman, the pattern is biphasic; lower prior to ovulation with a sudden, but sustained temperature increase.
The test is most accurately performed when the woman checks her temperature just after waking. The same thermometer should be used throughout the cycle and the woman should refrain for activity prior to registering the temperature. The temperature can then be logged throughout the course of the cycle. Any condition affecting the woman may affect temperature registration including: illness, alcohol consumption, medications, changes in sleep patterns as well as changes in sleeping environments
It is a good method to establish a pattern to ovulation and for documenting the length of each stage of the menstrual cycle. However, its ability to predict the LH surge falls short. It can predict the ovulatory trigger the day it occurs in less than one-third of women and can predict a two-day window of ovulation in approximately two-thirds of women. In brief, as a general screening tool it offers low cost and accessibility with limited accuracy and need for rigorous patient commitment.
Accompanying the rise in temperature during the ovulatory change is an alteration in the consistency of cervical mucus. The cervical mucus increases in volume and becomes more elastic, or tacky. Its accuracy in predicting ovulation within one day is comparable to BBT in motivated patients (up to 70%). A clear advantage to this test is that it is free and requires only observation without invasive testing. It is marred, however, but its high subjectivity and time needed to train women to evaluate subtle changes in cervical mucus.
With the progesterone rise and accompanying cervical mucus alterations comes changes in the composition of saliva. There is an increase in the salt (NaCl) concentration peri-ovulation. When salt-laden saliva dries, (for instance, on a slide) it crystallizes causing a pattern similar to a common household fern’s leaf; hence “ferning” can be used to calibrate the periovulatory period. Predictably, its accuracy is akin to that of BBT and cervical mucus sampling. There are confounding factors than may affect the ability of the saliva to fern including estrogen levels or bubbles within the saliva itself. To improve accuracy, some companies attempt to quantify these measures and combined tests for both saliva and vaginal secretions are available although with little improvement in the accuracy.