There are relatively few published prospective studies that estimate cumulative pregnancy rates among couples trying to achieve pregnancy with the use of natural markers of fertility. Previous studies are mostly retrospective or exclude infertile couples. Researchers from the University of Dusseldorf and Heidelberg recently reported the largest prospective study among volunteer couples using the sympto-thermal method (STM) of natural family planning (i.e., mucus symptoms and temperature shift) to achieve pregnancy.(1) The purpose of the study was to estimate the cumulative probabilities of conception (CPC) among a cohort of couples using natural family planning from their first cycle onwards.
The German researchers recruited 346 couples that indicated a desire to achieve a pregnancy from 1,357 couples that were taught the STM by experienced NFP teachers. The 346 couples were observed from the first cycle they attempted to achieve a pregnancy. Pregnancies were confirmed by ultrasound, a positive pregnancy test, or a luteal phase greater than 18 days. Prior to each cycle the volunteer couple indicated their intention to achieve a pregnancy and during that cycle recorded all acts of intercourse. Cycles that did not have at least one act of intercourse during the fertile phase were excluded. This turned out to be about 3% of the cycles in the study. The mean age of the women volunteers was 29.0 ± 3.6 (range 20-44) and the mean age of their male partners was 31.6 ± 5.5. There were a total of 310pregnancies among the346 couples during amaximumof 29 cycles of observation. The researchers labeled the couples that achieved a pregnancy as "truly fertile (TF)."
The cumulative pregnancy rates for cycles 1,3,6 and 12 for all couples (N = 340) were 0.38, 0.68, 0.81, and 0.92 respectively. For the TF couples (N = 304) the pregnancy rates at cycles 1, 3, 6, and 12 were 0.42, 0.75, 0.88, and 0.98. Therefore, close to 90% of the TF couples and close to 80% of all couples in the study achieved a pregnancy within the first 6 cycles of fertility-focused intercourse. A total of 8% of all the volunteer couples failed to conceive with the first 12 cycles of trying and were considered sub-fertile. For approximately 30% of these couples this was a secondary infertility (i.e., couples who had conceived at least once in the past). The researchers also found a significant age-related decrease in CPC for all the couples (i.e., the combination of the truly fertile and sub-fertile couples). However, among the TF couples there was no sign)ficant age-related decrease in CPC.
Based on the findings from this prospective CPC study, the researchers made some clinical recommendations.(1-2) They concluded that since almost 20% of couples do not achieve pregnancy within 6 cycles of fertility-focused intercourse (and approximately 10% of truly fertile couples) that almost every second couple is either sub-fertile or infertile after 6 cycles of trying to achieve a pregnancy. Therefore, they proposed a new threshold of referring for or initiating a basic infertility work-up by a primary care provider; i.e., they recommended referring couples that have 6 cycles of fertility-focused intercourse utilizing STM without achieving a pregnancy for a primary infertility workup. However, if the couple in question has a good prognosis (i.e., no unexplained infertility, no tubal defects, low spenm counts, no oligoamenorhoea, and no signs of reduced ovarian reserve) and the woman's age is less than 35 years, they recommended only fertility-focused intercourse during the next 36 months - i.e., these couples have a fairly good chance (greater than 60%) of achieving within that time period. Finally they also recommended an advanced infertility work-up for couples with a poor prognosis and 12 unsuccessful cycles with fertility-focused intercourse.
The results and recommendations from this study are similar to those of a smaller study conducted by Hilgers and others with the Creighton Model FertilityCare™ (CrMS) ovulation method.(3) Hilgers also has recommended infertility work-up referral for couples that practice fertility focused intercourse with the CrMS and do not achieve within 6 months of trying. The normal practice is for a couple to have at least 12 months of random unprotected intercourse before an infertility workup would be recommended. The recommendation that couples who have a primary infertility work up and have no tubal defects, anovulation, and oligospermia just use NFP for the next three years could save a lot of money and avoid expensive advanced reproductive techniques. However, besides utilizing NFP to determine the fertile window for fertility focused intercourse, I would also recommend lifestyle changes that would help increase the chances of pregnancy, i.e., proper diet, exercise, stress management, no smoking, and rest.(RJF)
1. Gnoth, C., Godehardt, D., Godehardt, E., et al. Time to pregnancy: results of the German prospective study and impact on the management of infertility. Human Reproduction. 2003;18:1959-1966.
2. Gnoth, C., Frank-Hermann, P.m. and Freundl, G. Opinion: Natural family planning and the management of infertility. Archives of Gynecology and Obstetrics. 2002;267:67-71.
3. Hilgers, T.W., Daly, K.D., Prebil, A.M. and Hilgers, SX. Cumulative pregnancy rates in patients with apparently normal fertility and fertility-focused intercourse. Journal of Reproductive Medicine. 1992:37:864-866.