Basal body temperature assessment: is it useful to couples seeking pregnancy?

The risks of the natural family planning methods

Zufferey MM, 1986·Ther Umsch

Risks of 5 natural family planning (NFP) methods are compared. The main risk of these methods is the risk of pregnancy stemming from method failure, errors in instruction, error in application of the method, and failure to observe abstinence during the entire fertile period. The calendar rhythm method, the oldest NFP method, is based on calculation of likely fertile days in the preceding 6-12 menstrual cycles. The method is seldom taught at present because of its high failure rate, but it continues to be used, often by individuals with an incomplete understanding of the calculations. The principle of the basal body temperature method is well known. The thermal shift affirms the beginning of the infertile period but does not allow prediction of ovulation. Instructions provided by different organizations to identify the third day of the hyperthermal plateau are not standardized; the various interpretations applied to the same cycle do not necessarily lead to identification of the same day as the start of the infertile period. Comparisons of efficacy between methods are therefore difficult. Well-conducted prospective studies have demonstrated high theoretical efficacy, but failure rates in practice appear to be higher. Women often do not know how to interpret a temperature curve correctly, and the curve may be influenced by illness, sleeping late, a change of life style or thermometer. Some authors have reported that 3-20% of ovulatory cycles have monophasic temperature curves. The temperature method requires lengthy abstinence lasting until the third day of higher temperature, which may create conflicts in some couples. To ease the difficulties of interpretation of the temperature method, a Swiss architect developed an electronic thermometer programmed according to rules of the calendar rhythm method for cycles of 19-39 days. The woman's 6 most recent cycle lengths remain in the memory to indicate probable infertile days. Although no formal evaluations have appeared in the literature on the Bioself thermometer, the method appears to entail risks including registration of incorrect temperature due to humidity or rundown batteries, and inadequate programming to identify the safe period. The Billings or cervical mucus method is based on observation by the woman of the thickness, wetness, and other characteristics of mucus secretions in the vulva to predict ovulation. Various studies have shown high theoretical efficacy but practical efficacy is lower. Vaginal infections, some ovarian pathologies, and postpartum hormonal changes are among factors that can alter mucus patterns. The method does not confirm ovulation, and false "peak days" may occur. The symptothermal method is based on all the principles of the cervical mucus and temperature methods as well as autopalpation of the cervix and any other signs of ovulation. Effectiveness rates are high. In general pregnancy risks are the same as those for the cervical mucus and temperature methods. A theoretical heightened risk of abortion or fetal malformation common to all the methods due to fertilization of aging gametes has not been definitively evaluated. Another possible risk results from timing of abstinence at the phase of the menstrual cycle when the woman's sexual desire is likely to be greatest.

Psychologic aspects of the basal body temperature method of regulating births

Marshall J et al., 1970·Fertil Steril

Effectiveness of a Natural Family Planning Service Program

Fehring RJ et al., 2016·MCN Am J Matern Child Nurs

The aims of this study were to determine and compare extended use-effectiveness of an online nurse-managed fertility education service program among women (and subgroups of women) seeking to avoid pregnancy. This was a 24-month prospective study of a university-based online Web site with 663 nonbreastfeeding women using an online charting system to avoid pregnancy. Participants tracked their fertility online with either cervical mucus monitoring, electronic hormonal fertility monitoring, or both fertility indicators. Unintended pregnancies were validated by professional nurses. Participants had a mean age of 30.4 years (SD = 6.3) and mean 1.7 children (SD = 2.0). Among the 663 nonbreastfeeding participants there were 2 unintended pregnancies per 100 at 24 cycles of correct use and 15 pregnancies at 24 cycles of typical use. However, the 212 women using the electronic fertility monitor had a typical use unintended pregnancy rate of 6 at 24 cycles of use in comparison with the 118 women using cervical mucus monitoring that had a typical use pregnancy rate of 19 at 24 cycles and with the 333 women using both fertility indicators that had a pregnancy rate of 18 at 24 cycles of use. Use of the fertility monitor to estimate fertility among nonbreastfeeding women provides the most secure method of avoiding pregnancy.

Efficacy of achieving pregnancy with fertility-focused intercourse

Mu Q et al., 2013·MCN Am J Matern Child Nurs

To compare pregnancy rates when women have intercourse on self-estimated high and peak fertile days and when they only have intercourse on low fertile days during the fertile window (FW). We used a prospective observational cohort study design. Our convenience sample included 124 women who utilized our online charting Web sites to achieve pregnancy from January 2010 to November 2012. Participants used an electronic hormonal fertility monitor (EHFM) or self-observed cervical mucus or both to determine fertility during the estimated FW. Pregnancy rates were determined with Kaplan-Meier survival analysis. Chi square analysis was used to evaluate the efficacy of achieving pregnancy between two different intercourse patterns. The pregnancy rate was 87 per 100 women at 12 months when intercourse happened on high or peak days and 5 per 100 when intercourse occurred only on low days of the FW. Chi square analysis showed a greater proportion of pregnancies with intercourse on high and peak fertile days of the menstrual cycle (x2 = 40.2, p < .001, df = 1). Focusing intercourse on high or peak fertile days during the estimated FW enhances the probability of achieving a desired pregnancy. Fertility awareness-based online charting system is effective in helping women to determine their FW and target intercourse accordingly to achieve pregnancy.