techniques ovulation predictor kits (opks) can detect imminent ovulation from the concentration of luteinizing hormone (lh) in a woman's urine. a positive opk is usually followed by ovulation within 12–36 hours. saliva microscopes, when correctly used, can detect ferning structures in the saliva that precede ovulation. ferning is usually detected beginning three days before ovulation, and continuing until ovulation has occurred. during this window, ferning structures occur in cervical mucus as well as saliva. computerized fertility monitors, such as lady-comp, are available under various brand names. these monitors may use bbt-only systems, they may analyze urine test strips, they may use symptothermal observations, they may monitor the electrical resistance of saliva and vaginal fluids, or a combination of any of these factors. a symptohormonal method of fam developed at marquette university uses the clearblue easy fertility monitor to determine the fertile window. the monitor measures estrogen and lh to determine the peak day. this method is also applicable during postpartum, breastfeeding, and perimenopause, and requires less abstinence than other fam methods. some couples prefer this method because the monitor reading is objective and is not affected by sleep quality as bbt can be. benefits and drawbacks fertility awareness has a number of unique characteristics: fa can be used to monitor reproductive health. changes in the cycle can alert the user to emerging gynecological problems. fa can also be used to aid in diagnosing known gynecological problems such as infertility. fa is versatile: it may be used to avoid pregnancy or to aid in conception. use of fa can give insight to the workings of women's bodies, and may allow women to take greater control of their own fertility. some symptoms-based forms of fertility awareness require observation or touching of cervical mucus, an activity with which some women are not comfortable. some practitioners prefer to use the term "cervical fluid" to refer to cervical mucus, in an attempt to make the subject more acceptable to these women. some drugs, such as decongestants, can change cervical mucus. in women taking these drugs, the mucus sign may not accurately indicate fertility. some symptoms-based methods require tracking of basal body temperatures. because irregular sleep can interfere with the accuracy of basal body temperatures, shift workers and those with very young children, for example, might not be able to use those methods. fa requires action daily—detailed record keeping. some may find the time and detail requirements too complicated. as birth control by restricting unprotected sexual intercourse to the infertile portion of the menstrual cycle, a woman and her partner can prevent pregnancy. during the fertile portion of the menstrual cycle, the couple may use barrier contraception or abstain from sexual intercourse. advantages there are no drug-related side effects to fa. fa can be free or have a very low up-front cost. users may employ a coach, use computer software, or buy a chart, calendar, or basal thermometer. the direct costs are low when compared to other methods. fa can be used with barrier contraception so that intercourse may continue through the fertile period. unlike barrier use without fa, practicing fa can allow couples to use barrier contraception only when necessary. fa can be used to immediately switch from pregnancy avoidance to pregnancy planning if the couple decides it is time to plan for conception. disadvantages use of a barrier or other backup method is required on fertile days; otherwise the couple must abstain. to reduce pregnancy risk to below 1% per year, there are an average of 13 days where abstinence or backup must be used during each cycle. for women with very irregular cycles—such as those common during breastfeeding, perimenopause, or with hormonal diseases such as pcos—abstinence or the use of barriers may be required for months at a time. typical use effectiveness is lower than most other methods. fertility awareness does not protect against sexually transmitted disease. effectiveness the effectiveness of fertility awareness, as of most forms of contraception, can be assessed two ways. perfect use or method effectiveness rates only include people who follow all observational rules, correctly identify the fertile phase, and refrain from unprotected intercourse on days identified as fertile. actual use or typical use effectiveness rates include all women relying on fertility awareness to avoid pregnancy, including those who fail to meet the "perfect use" criteria. rates are generally presented for the first year of use. most commonly, the pearl index is used to calculate effectiveness rates, but some studies use decrement tables. the failure rate of fertility awareness varies widely depending on the system used to identify fertile days, the instructional method, and the population being studied. some studies have found actual failure rates of 25% per year or higher. at least one study has found a failure rate of less than 1% per year with continuous intensive coaching and monthly review, and several studies have found actual failure rates of 2%–3% per year. when used correctly and consistently (i.e., with perfect use) with ongoing coaching, under study conditions some studies have found some forms of fa to be 99% effective. from contraceptive technology: post-ovulation methods (i.e., abstaining from intercourse from menstruation until after ovulation) have a method failure rate of 1% per year. the symptothermal method has a method failure rate of 2% per year. cervical mucus–only methods have a method failure rate of 3% per year. calendar rhythm has a method failure rate of 9% per year. the standard days method has a method failure rate of 5% per year. reasons for lower typical-use effectiveness several factors account for typical-use effectiveness being lower than perfect-use effectiveness: conscious user non-compliance with instructions (having unprotected intercourse on a day identified as fertile) mistakes on the part of those providing instructions on how to use the method (instructor providing incorrect or incomplete information on the rule system) mistakes on the part of the user (misunderstanding of rules, mistakes in charting) the most common reason for the lower actual effectiveness is not mistakes on the part of instructors or users, but conscious user non-compliance—that is, the couple knowing that the woman is likely to be fertile at the time but engaging in sexual intercourse nonetheless. this is similar to failures of barrier methods, which are primarily caused by non-use of the method. to achieve pregnancy intercourse timing a 2015 review found insufficient evidence to draw any conclusions about the effect of timing intercourse on the rate of live births or pregnancies, compared to regular intercourse. a study by barrett and marshall has shown that random acts of intercourse achieve a 24% pregnancy rate per cycle. that study also found that timed intercourse based on information from a bbt-only method of fa increased pregnancy rates to 31%–68%. studies of cervical-mucus methods of fertility awareness have found pregnancy rates of 67–81% in the first cycle if intercourse occurred on the peak day of the mucus sign. because of high rates of very early miscarriage (25% of pregnancies are lost within the first six weeks since the woman's last menstrual period, or lmp), the methods used to detect pregnancy may lead to bias in conception rates. less-sensitive methods will detect lower conception rates, because they miss the conceptions that resulted in early pregnancy loss. a chinese study of couples practicing random intercourse to achieve pregnancy used very sensitive pregnancy tests to detect pregnancy. it found a 40% conception rate per cycle over the 12-month study period. pregnancy rates for sexual intercourse are also affected by several other factors. regarding frequency, there are recommendations of sexual intercourse every 1 or 2 days, or every 2 or 3 days. studies have shown no significant difference between different sex positions and pregnancy rate, as long as it results in ejaculation into the vagina. social science research has found that timing intercourse can become a gendered 'chore' in heterosexual married couples trying to conceive, with women tracking their ovulation cycles and dictating to their husbands when they should have sexual intercourse. problem diagnosis regular menstrual cycles are sometimes taken as evidence that a woman is ovulating normally, and irregular cycles as evidence she is not. however, many women with irregular cycles do ovulate normally, and some with regular cycles are actually anovulatory or have a luteal phase defect. records of basal body temperatures, especially, but also of cervical mucus and position, can be used to accurately determine if a woman is ovulating, and if the length of the post-ovulatory (luteal) phase of her menstrual cycle is sufficient to sustain a pregnancy. fertile cervical mucus is important in creating an environment that allows sperm to pass through the cervix and into the fallopian tubes where they wait for ovulation. fertility charts can help diagnose hostile cervical mucus, a common cause of infertility. if this condition is diagnosed, some sources suggest taking guaifenesin in the few days before ovulation to thin out the mucus. pregnancy testing and gestational age pregnancy tests are not accurate until 1–2 weeks after ovulation. knowing an estimated date of ovulation can prevent a woman from getting false negative results due to testing too early. also, 18 consecutive days of elevated temperatures means a woman is almost certainly pregnant. estimated ovulation dates from fertility charts are a more accurate method of estimating gestational age than the traditional pregnancy wheel or last menstrual period (lmp) method of tracking menstrual periods.