Sex ratio associated with timing of insemination and length of the follicular phase in planned and unplanned pregnancies during use of natural family planning.

This was a multicentred, prospective study of pregnancies among women using natural family planning. The women maintained natural family planning charts of the conception cycle, recording acts of intercourse and signs of ovulation (cervical mucus changes, including peak day and basal body temperature). Charts were used to assess the most probable day of insemination relative to the day of ovulation and length of the follicular phase of the cycle. The sex ratio (males per 100 females) for 947 singleton births was 101.5, not significantly different from the expected value of 105. The sex ratio did not vary consistently or significantly with the estimated timing of insemination relative to the day of ovulation, with the estimated length of the follicular phase or with the planned or unplanned status of the pregnancy. Although these findings may be affected by imprecision of the data, the study suggests that manipulation of the timing of insemination during the cycle cannot be used to affect the sex of offspring.

PIP: In the context of ongoing debate over the determinants of sex ratio, the authors used data from a multinational study of pregnancies among natural family planning (NFP) users to investigate the association between timing of conception or follicular phase and length and the sex ratio at birth. They also explored whether a pregnancy's planned or unplanned status affects those associations. A multicenter, prospective study of pregnancies among women using NFP was conducted. The women maintained NFP charts of their conception cycles, recording acts of intercourse and signs of ovulation such as cervical mucus changes and basal body temperature. Charts were used to identify the most probable day of insemination relative to the day of ovulation and length of the follicular phase of the cycle. The sex ratio (number of males per 100 females) for 947 singleton births was 101.5, not significantly different from the expected value of 105. The sex ratio did not vary consistently or significantly with the estimated timing of insemination relative to the day of ovulation, with the estimated length of the follicular phase, or with the planned or unplanned status of the pregnancy. Study findings suggest that manipulating the timing of insemination during the cycle cannot be used to affect the sex of offspring.

Effects of timing of conception on birth weight and preterm delivery of natural family planning users.

OBJECTIVE: Various birth defects and untoward perinatal outcomes have been claimed to be associated with pregnancies conceived by gametes aged in vivo before fertilization. Thus, these outcomes were systematically assessed in pregnancies occurring in natural family planning (NFP) users. Our international multicenter cohort study of NFP pregnancies (n = 877) is by far the largest systematic study designed to assess pregnancy outcome and is of sufficient power to allow us to address the concern of low birth weight (< 2500 g) and preterm delivery (< 37 weeks gestation). STUDY DESIGN: In addition to gathering baseline medical data, evaluation was performed at 16 weeks, 32 weeks and at term. Data were collected in a systematic cohort fashion, verified by the five collaborating international recruiting centers, and analyzed by investigators in the US. Most recruiting center principal investigators are obstetrician-gynecologists and, if not, have integral relationships with such specialists. Standard criteria could thus be applied within and among centers. In our cohort, birth weight was recorded accurately at delivery. Almost all of the deliveries occurred in hospitals; thus, data should be quite reliable. Neonatal examination for anomalies was usually conducted immediately after delivery, when birth weight was recorded. RESULTS: Analysis of risk factors for low birth weight and preterm delivery showed that this population had a low risk profile. Low birth weight infants (< 2500 g) and preterm deliveries were increased among women with a history of either prior low birth weight or preeclampsia in the index pregnancy. However, mean birth weight was unaffected by the timing of conception vis à vis ovulation or pregnancy history. Mean birth weight for the 877 singleton NFP pregnancies was 3349.6 g. The risk of preterm delivery was increased among older women who drank alcohol, but there were no significant effects of timing of conception vis à vis ovulation on preterm delivery. Results held when analysis was stratified according to whether NFP was being used for contraception or to achieve pregnancy. CONCLUSIONS: Our data do not appear to show striking differences between 877 NFP pregnancies and the general obstetric population. The timing of conception vis à vis ovulation does not exert significant effects on the birth weight or preterm delivery of resulting pregnancies, a reassuring finding for NFP users.

Pregnancy complications in natural family planning users.

A multicenter cohort study was designed to assess pregnancy outcome among natural family planning (NFP) users, and provide the opportunity to address complications in NFP users by planning status and by timing of conception with respect to day of ovulation. There were 877 singleton births in this sample. Complications evaluated were abnormal vaginal bleeding, urinary tract infection, vaginal infection, hypertension of pregnancy, proteinuria, glycosuria, and anemia. There was no significant difference in the mean age, number of prenatal visits or birth weight among optimally and non-optimally timed pregnancies or for planned and unplanned pregnancies. There were higher incidences of "parity 2 or more" and current smokers in the non-optimally timed pregnancies and lower incidences of prior pregnancy loss and "currently employed" in the non-optimally timed pregnancies. There was little difference in pregnancy complications with respect to pregnancy timing, with the exception of a significant increased risk of vaginal bleeding late in pregnancy among non-optimally timed conceptions (11.5%) compared to optimally timed pregnancies (5.2%, RR = 2.2, 95% CI 1.3-3.7). More differences were observed in pregnancy complication rates by planning status. Unplanned pregnancies were associated with significantly more late pregnancy bleeding, vaginal infections, proteinuria, glycosuria and medication use than planned pregnancies. Unplanned pregnancies had lower incidences of maternal anemia. Complications of pregnancy were low in this NFP population, irrespective of planned versus unplanned status. Women with planned pregnancies had even fewer complications during pregnancy than women with unplanned conceptions, suggesting that women using NFP to plan their reproduction may be at particularly low risk.

Pregnancy outcome in natural family planning users: cohort and case-control studies evaluating safety.

Conceptions involving aging gametes are of relevance to natural family planning (NFP) because women using NFP to avoid pregnancy abstain from intercourse during the fertile time of the cycle. To help verify the safety of pregnancies occurring among NFP practitioners, our group has, since 1986, conducted a large cohort study involving six experienced NFP centers. Timing of conception was determined from NFP charts, in which women recorded days on which intercourse occurred. The number of days from the most probable conception intercourse to probable day of ovulation was first determined, and used as an estimate of the time gametes remained in the genital tract before fertilization. Several studies have already been completed, cohort as well as case-control in nature.

Adverse outcomes of planned and unplanned pregnancies among users of natural family planning: a prospective study.

OBJECTIVES: The purpose of this study was to determine prospectively whether unplanned pregnancies are associated with adverse pregnancy outcomes among users of natural family planning. METHODS: Women who became pregnant while using natural family planning were identified in five centers worldwide: there were 373 unplanned and 367 planned pregnancies in this cohort. The subjects were followed up at 16 and 32 weeks' gestation and after delivery. The risks of spontaneous abortion, low birth-weight, and preterm birth were estimated after adjustment by logistic regression. RESULTS: The women with unplanned pregnancies were more likely to be at the extremes of age, to report more medical problems before and during the index pregnancy, and to seek antenatal care later in gestation than the women with planned pregnancies. However, women with planned pregnancies reported a higher rate of spontaneous abortion in previous pregnancies (28.8%) than did women with unplanned pregnancies (12.9%). There were no significant differences in the rates of spontaneous abortion, low birthweight, or preterm birth between the two groups. CONCLUSIONS: No increased risk of adverse pregnancy outcomes was observed among women who experienced an unplanned pregnancy while using natural family planning.

Further evidence that infection is an infrequent cause of first trimester spontaneous abortion.

A previous cohort study found no clinical evidence that infection occurred more often in subjects experiencing pregnancy loss compared with those experiencing successful pregnancy [Simpson et al. (1996) Hum. Reprod., 11, 668-672]. Given these surprising findings, we conducted a similar analysis on another cohort also followed prospectively. Using couples practising natural family planning for conception or contraception, information on clinical evidence of infection was gathered beginning with week 5 of gestation. Information on fever and signs of overt infection was specifically sought by interview and physical examination. Frequencies of urinary, vaginal and other infections in subjects experiencing pregnancy loss were 11.1, 9.5 and 8.7% respectively, not significantly different from rates in subjects having liveborns (10.1, 10.2 and 10.3% respectively). Thus, no association between clinical infection and early pregnancy loss (< or = 16 weeks) was observed. Cohort studies utilizing biologically based assays are awaited because extant data do not provide evidence that clinically evident infections play major roles in first trimester pregnancy losses.

Calendar rhythm efficacy: a review.

OBJECTIVE: To estimate the unplanned pregnancy rate of calendar rhythm. DESIGN: Meta-analysis of eight studies of calendar rhythm published between 1940 and 1989. RESULTS: There exist few studies of the calendar rhythm method. Analysis of the best of these studies resulted in a conservative estimated Pearl rate of 18.5 +/- 1.8, and a less conservative estimate of 15.0 +/- 4.0, standardized to 12 months' observation; these results are in the range of other natural and barrier methods. DISCUSSION: We need properly done clinical trials of the calendar rhythm method to scientifically establish its effectiveness.

Timing of conception and the risk of spontaneous abortion among pregnancies occurring during the use of natural family planning.

OBJECTIVE: Our purpose was to ascertain the effects of timing of conception on the risk of spontaneous abortion. STUDY DESIGN: To assess these effects, women who conceived while using natural family planning were identified in five centers worldwide between 1987 and 1993. Timing of conception was determined from 868 natural family planning charts that recorded day of intercourse and indices of ovulation (cervical mucus peak obtained according to the ovulation method and/or basal body temperature). Conceptions on days - 1 or 0 with respect to the natural family planning estimated day of ovulation were considered to be "optimally timed," and all other conceptions were considered as "non-optimally timed." The rate of spontaneous abortions per 100 pregnancies was examined in relation to timing of conception, ages, reproductive history, and other covariates with bivariate and multivariate statistical methods. RESULTS: There were 88 spontaneous abortions among 868 pregnancies (10.1%). The spontaneous abortion rate was similar for 361 optimally timed conceptions (9.1%) and 507 non-optimally timed conceptions (10.9%). However, among 171 women who had experienced a spontaneous abortion in a prior pregnancy, the rate of spontaneous abortion in the index pregnancy was significantly higher with non-optimally timed conceptions (22.6%) as compared with optimally timed conceptions (7.3%). This association was not observed among 697 women with no history of pregnancy loss. The adjusted relative risk of spontaneous abortion among women with non-optimally timed conceptions and a history of pregnancy loss was 2.35 (95% confidence intervals 1.42 to 3.89). The excess risk of spontaneous abortion was observed with both preovulatory and postovulatory conceptions. CONCLUSIONS: Overall, there is no excess risk of spontaneous abortion among the pregnancies conceived during natural family planning use. However, among women with a history of pregnancy loss, there is an increased risk of spontaneous abortion associated with preovulatory or postovulatory delayed conceptions.

PIP: The results of a large, multicenter study suggest that users of natural family planning are not at increased risk of spontaneous abortion, even when conceptions are not optimally timed. Between 1987-93, data on timing of conception and spontaneous abortion were collected from the charts of 868 natural family planning clients at five centers in the US, Chile, Colombia (two sites), and Italy. This issue was investigated due to concerns that unplanned pregnancies arising from failures of the natural family planning method could be associated with aged gametes and adverse pregnancy outcomes. The day of peak mucus was used as the marker for estimating ovulation. The number of days from the most probable conception intercourse to probable day of ovulation provided an estimate of the time the gametes remained in the reproductive tract before fertilization; less than 48 hours was considered optimal. There were 88 spontaneous abortions (10.1%) and eight stillbirths (0.92%) in this series. Of the 361 conceptions judged to have occurred during the optimal time frame, 33 (9.1%) were spontaneously aborted. The miscarriage rate among the 507 conceptions that occurred at nonoptimal times was 10.9% (55). The difference was not statistically different. Among the 171 women with a previous pregnancy loss, an optimally timed conception in the index pregnancy was associated with a low rate of miscarriage (7.3%). There was, however, an excess rate of spontaneous abortion (22.6%) in women with a prior miscarriage and a pre- or post-ovulatory conception in the recent pregnancy. Although the biologic reasons for this finding are unclear, it is recommended that women with a prior spontaneous abortion use the ovulation method mucus peak or the basal body temperature rise to conceive during the optimal time.

Trial of a new method of natural family planning in Liberia.

This paper describes the evaluation of a new method of natural family planning (NFP) in Liberia. The Modified Mucus Method (MMM) was developed to address the need for a simple method of charting for poor and illiterate women. The acceptance, use, and cost-effectiveness of the MMM were compared with standard NFP methods, the sympto-thermal and ovulation method (ST/OM), used in the same population. The personal discontinuation rate of MMM users was 27.3 per 100 women per year compared with 3.2 among ST/OM users. Unplanned pregnancy rates were low for both MMM and ST/OM, 6.6 and 1.5 respectively. The cost per couple year protection (CYP) for MMM was $55.80 and for ST/OM $56.10. There were differences in characteristics between MMM and ST/OM clients. The MMM clients were more likely to have attended school and to have used a family planning method previously, and were less likely to be housewives. We conclude that the MMM in Liberia was provided to an inappropriate sample of women, educated and middle-class rather than poor and illiterate. The MMM users were dissatisfied and discontinued at the rate of 44 per 100 women entering per year. This is an unfair evaluation of the MMM because of the unsuitable study population. It is our opinion that the MMM needs more study to become part of the inventory of birth spacing methods.

Roman Catholic Church-sponsored natural family planning services in the United States.

OBJECTIVES: Our objective was to determine the level and quality of natural family planning service provided by Roman Catholic Diocese-related programs in the United States. STUDY DESIGN: Programs volunteered quarterly data for five years, using least squares regression we estimated service levels for programs never reporting. RESULTS: From 1988 to 1992, 78 dioceses ever reported and 96 never reported. The majority of clients were avoiding pregnancy and receiving follow-up. An average of 18,061 women were taught by these programs each year in the reporting period. CONCLUSION: Without greater commitment of resources, it is likely that NFP will continue to be a marginal method of family planning in the United States.

Evaluation of natural family planning programmes in Liberia and Zambia.

Studies to evaluate use-effectiveness and cost-effectiveness of natural family planning (NFP) were conducted in Liberia and Zambia. The Liberian programme provided uni-purpose NFP services to 1055 clients mainly in rural areas; the Zambian programme provided NFP services integrated with MCH to 2709 clients predominantly in urban areas. The one-year life table continuation and unplanned pregnancy rates were 78.9 and 4.3 per 100 woman-years in Liberia, compared to 71.2 and 8.9 in Zambia. However, high rates of loss to follow-up mandate caution in interpretation of these results, especially in Zambia. More women progressed to autonomous NFP use in Liberia (58%) than in Zambia (35.3%). However, programme costs per couple-year protection were lower in Zambia (US$25.7) than in Liberia (US$47.1). Costs per couple-year protection were higher during learning than autonomy, and declined over time. These studies suggest that NFP programmes can achieve acceptable use- and cost-effectiveness in Africa.

PIP: A team evaluated the use-effectiveness and cost-effectiveness of natural family planning (NFP) programs in Liberia and Zambia, both of which focused on sympothermal and ovulation methods. Accounting records were used to conduct the cost-effectiveness evaluation. Most women accepted NFP to prevent pregnancy (82.6% in Liberia and 73.2% in Zambia). Women in Liberia were more likely to complete the learning phase and to progress to autonomous use than those in Zambia (58% vs. 35.3%; p .001). User characteristics which contributed greatly to NFP performance included breast feeding and delivery within 6 months of beginning NFP (p .001) and intention to space births (p .01). Program factors were number of teacher-client contacts/month for all users and mean duration of learning phase (p .001) (2.4 for Liberia vs. 1.2 for Zambia and 8.5 vs. 13.2, respectively). Discontinuations due to change of pregnancy intention and for personal reasons were essentially equal in both programs. Change of pregnancy intention was more common during the learning phase. Unplanned pregnancies were more common in Zambia than Liberia (8.9/100 woman-years vs. 4.3/100 woman/years; p .01). In fact, they were higher in Zambia than in Liberia during the learning and autonomous phases (8.1 vs. 3.7; p .01 and 10.6 vs. 4.6; p .01, respectively). The Zambian NFP program had higher 12-month total discontinuation rates than the Liberian NFP program (28.8 vs. 21.2; p .01). Slow implementation of a techer supervisory system in Zambia resulted in a high rate of loss to follow-up (36.7). In Liberia, this rate was 15.7. Higher client recruitment in Zambia contributed to lower program costs/couple years of protection (CYP) (US$25.7 vs. US$47.1 for Liberia). The costs/CYP were much lower during the autonomous phase than the learning phase in both programs and fell over time. These findings indicated that NFP programs can realize adequate use- and cost-effectiveness in Africa.

Fetal outcome among pregnancies in natural family planning acceptors: an international cohort study.

This international, multicenter, prospective cohort study examines the outcome of pregnancies associated with aging gametes. Comparing pregnancies conceived at or near the peak mucus phase with those occurring before or after the peak provides a means of evaluating the effect of aging gametes. The outcome criteria are (1) rates of spontaneous abortion, (2) low birth weight, and (3) congenital malformations. Preliminary analysis shows a trend toward increased spontaneous abortion with aging gametes in certain subsets (women with prior pregnancy losses) but no effect on birth weight. Too few method failures have yet been studied to make a definitive statement on congenital malformations.

PIP: 706 women from 6 centers in 5 countries (Chile, Peru, Colombia, United States and Italy) were involved in a study of the fetal outcome of natural family planning (NFP) acceptors. The women used symptothermal or mucus methods. The results of a prelimary analysis showed that pregnancy loss is not greater in this NFP population; 7.9% (50/629). There were fewer pregnancy losses among pregnancies conceived + or - 1 day of the mucus peak compared to those conceived 2 days before the mucus peak, which means aging sperm, or 2 days after, which means aging oocytes. This trend becomes significant for those women with pregnancy losses from previous pregnancies and is not related to maternal age. The use of the natural family planning method appears to be unrelated to health effects on liveborn infants. Neither birth length, birth weight, nor head circumference were correlated with the timing of conception. Recruitment is underway to enlarge the sample for a more thorough analysis of the relationship between timing of conception and congenital anomalies. Further analysis is also underway for exploring the day of conception in relations to the mucus peak and pregnancy loss. Data collection for this multicenter study involves the collection of NFP data when pregnancy is 1st recognized. The likely date of conception is determined by an independent panel of experts who are unaware of the pregnancy outcome. An extensive body of information is collected at the intake meeting, at 16 weeks, and then at 32 weeks. In the systematic neonatal examination, major and minor anomalies, birth weight, and other neonatal characteristics are recorded. The analysis involved the comparison of NFP method failure and NFP user failure/planners.

Natural family planning use-effectiveness and continuation.

Numerous studies have been conducted to assess the use-effectiveness of natural family planning. However, because of imprecise definitions of terms, these studies show noncomparable results. Special effort is required to study natural family planning use-effectiveness by the same criteria as other family planning methods.

PIP: There is a 10-15-year time lag between scientific evaluation of medical contraception and measurement. As a result, NFP has been relegated to a subordinate status in the family planning field. Although NFP researchers can benefit from the time lab by adapting the data collection techniques and statistical approaches refined through decades of studies of modern contraceptive effectiveness, there are selected issues that only NFP research can resolve. For example, it must be determined whether an NFP client becomes a study subject at registration, when she is taught the method, when she begins to chart her cycles, or after she has had several months of experience with the method's use. Such clarification is especially important to the calculation of drop-out rates. Methodological problems in measuring use-effectiveness have led to noncomparable results for the same NFP method from country to country. An examination of NFP effectiveness studies conducted from 1981-90 reveals a median rate of 13/1, with a low of 2.5 for an ovulation method study conducted in Indonesia in 1990 and a high of 27.9 for an ovulation method study conducted in New Zealand in 1981. Studies completed after 1988 tend to document pregnancy rates lower than the median, presumably reflecting both improved methodology and NFP program development.

Factors related to autonomy and discontinuation of use of natural family planning for women in Liberia and Zambia.

From 1983 to 1988, natural family planning programs were conducted in Liberia and Zambia. In Liberia 1055 and in Zambia 2709 women used natural family planning to avoid pregnancy. These users could become pregnant, discontinue use of the method, or become autonomous users. Women who changed intention did not stop use of natural family planning and were not treated as discontinuations. In a multivariate analysis, client's age, breastfeeding status, employment, urban/rural residence, time of registration in the program, and visit intensity were significantly associated with the outcomes. The most consistent association was that women who entered the programs in the later time periods were more likely to become autonomous users and less likely to discontinue use of the method or to experience an accidental pregnancy.

PIP: As part of the evaluation of natural family planning (NFP) demonstration programs conducted in Liberia and Zambia from 1983-88, the factors associated with autonomous use, method discontinuation, and unplanned pregnancy were explored. There were 39 pregnancies recorded among the 1055 NFP acceptors in Liberia and 180 unplanned pregnancies among the 2709 acceptors in Zambia. A total of 144 Liberian and 465 Liberian women discontinued NFP use because of pregnancy or personal reasons. In both countries, housewives and women who were breastfeeding were less likely to become autonomous NFP users, while women who received a medium number of teacher-client visits per month and those who registered after the program had become established were more likely to become autonomous users. Similarly, women who registered later in both programs and had a medium or high number of home visits were less likely to discontinue method use. In Liberia, urban women were 7 times more likely than their rural counterparts to discontinue NFP. In Zambia, women over 35 years of age and those who were breastfeeding were significantly more likely to continue NFP use. The relative risk of an unplanned risk was greatest, in Zambia, among nonbreastfeeding women and, in Liberia, among urban women and, unexpectedly, women with a medium intensity of visits. Parity, maternal education, and birth spacing versus limiting intentions were not significantly predictors of outcome in either country. Although women who entered the NFP programs late in their development were more likely to become autonomous users and less likely to discontinue to experience unplanned pregnancy, no factor was consistently associated with all measures of NFP use in both programs.

Pregnancy outcome associated with natural family planning (NFP): scientific basis and experimental design for an international cohort study.

Although natural family planning (NFP) is a form of contraception without ostensible maternal risks (other than pregnancy), potential fetal risks could exist if aging gametes are involved in inadvertent fertilization. In the following report, we first review animal studies firmly establishing that aging sperm and aging oocytes (delayed fertilization) cause chromosomal abnormalities in mammals and other species. We next review human studies associating decreased coital frequency with trisomy and studies of NFP populations that generally show no increased frequency of anomalous offspring or spontaneous abortions. Our rationale for initiating an international cohort study is presented, along with the experimental design selected. Preliminary findings indicate that the experimental design chosen will indeed provide information allowing NFP safety to be assessed definitively.

Evaluating client autonomy in natural family planning.

A critical element for evaluation of natural family planning (NFP) methods is client autonomy. Autonomy in NFP refers to clients who can identify their fertile days and apply this method without teacher assistance. The results of this study show that clients who are autonomous have a 12-month continuation rate of 96.7% and a pregnancy rate of 1.7% after beginning charting. The non-autonomous clients had a 12-month continuation rate of 34.3% and a pregnancy rate of 24.8% after beginning charting, significantly different from the autonomous clients. Using a bivariate analysis, we found that women 30 years and older who had two children or more, and women in the same age group (30 years and older) who wanted to limit rather than space pregnancy were significantly more likely to become autonomous. These findings have implications for NFP programs and future evaluation efforts.

Epidemiological studies of natural family planning.

The prevalence of the use of natural family planning (NFP) can be estimated from sample surveys of married women in the reproductive ages (MWRA). Surveys in developed and developing countries during the past decade indicate that the prevalence of NFP use varies from 0 to 11%. In addition, if one considers NFP use in relation to other contraceptive methods, the percentage of all current contraceptors who use NFP varies from 1 to 35%. This suggests that NFP is an important method in certain countries. Pregnancy rates for NFP vary widely, but most reliable studies report 1-year life-table pregnancy rates between 10 and 25/100 woman-years. The Billings ovulation method consistently has higher pregnancy rates than the sympto-thermal method and NFP users generally have among the highest pregnancy rates compared to other methods. The major safety issue concerning NFP is the risk of adverse pregnancy outcomes associated with aged gametes. There are suggestions from a number of investigations that conceptions distant from ovulation have a higher risk of spontaneous abortion and a higher proportion of male births. The findings with respect to birth defects or multiple pregnancies are less consistent, although some studies have reported an increased risk of chromosomal anomalies.

PIP: This study discusses the epidemiology of natural family planning in terms of prevalence, use-effectiveness, and health risks and benefits. The prevalence of natural family planning among all women of reproductive age is 0-11% in developing countries and 1-13% in developed countries. Prevalence is highest in Catholic countries, such as Peru, the Philippines, Belgium, France, and Poland (11%, 9%, 12%, 7%, and 13% respectively). The number of current contraceptive users using natural family planning ranges from 1-35% in developing countries and 1-23% in developed countries. Life-table pregnancy rates for the Billings ovulation method and the sympto-thermal method vary from 11-26/100 woman-years. The range of user failures is 4-34/100 woman-years as compared with method failures of 0-13/100 woman-years. Pregnancy rates for the calendar rhythm method are higher. Among highly motivated users who want no more children, pregnancy rates are similar to those of diaphragm users and lower than those of users of other intercourse-related methods. The major risks of natural family planning are the risks associated with pregnancy generally, especially in countries with high maternal mortality, and the risks of abnormal pregnancy outcomes due to aged sperm from intercourse prior to the fertile period and aged ova from intercourse after it. Probabilities of conception are highest 1-2 days before estimated time of ovulation. There is an excess of male births conceived during the least fertile days, and the risk of spontaneous abortion doubles outside the period of peak fertility. Furthermore, there is growing but inconclusive evidence linking chromosome abnormalities to aged gametes.