Natural fertility and impact of lifestyle factors

INTRODUCTION — Health care providers frequently receive questions about an individual's fertility potential and the possible impact of specific behaviors or environment on fertility. Patients may seek information on baseline fertility, optimal timing and frequency of coitus to achieve pregnancy, and behaviors to optimize or avoid to improve their fertility.

This topics will discuss natural fertility and the impact of lifestyle on fertility. The evaluation and treatment of individuals with infertility is discussed separately.

●(See "Overview of infertility".)

●(See "Female infertility: Evaluation".)

●(See "Approach to the male with infertility".)

In this topic, when discussing study results, we will use the terms "woman/en", "man/en", or "patient(s)" as they are used in the studies presented. However, we encourage the reader to consider the specific counseling and treatment needs of transgender and gender diverse individuals.

TERMINOLOGY — Infertility is a "disease which generates disability as an impairment of function" [1]. It is defined as inability "to establish clinical pregnancy after 12 months of regular, unprotected sexual intercourse or due to an impairment of a person's capacity to reproduce either as an individual or with his/her partner" [2]. Fertility interventions may be started earlier than 12 months depending on the medical, sexual, and reproductive history; age; physical findings; and diagnostic testing. The terms "infertility" and "subfertility" are interchangeable.

Other terms used when discussing reproductive potential include [2]:

●Fecundity is clinically defined as the capacity to have a live birth.

●Fecundability is the probability of achieving a pregnancy in a single menstrual cycle with adequate sperm exposure and no contraception that results in a live birth.

●Fertility is the ability to have a clinical pregnancy.

●Sterility is a permanent state of infertility.

●Time to pregnancy refers to the length of time, usually measured in months, that it takes a couple to conceive. This parameter is often used in epidemiological studies as a measure of subfecundity [3,4].

COMMON CLINICAL QUESTIONS

What is normal natural fertility? — Most pregnancies occur during the first six menstrual cycles of attempted conception [4-8]. Maximal fertility rates of approximately 30% per cycle have been reported in the first two cycles; fecundability decreases as the number of consecutive months without achieving pregnancy increases (figure 1) [5].

●Six months – In the first six months of attempting pregnancy, approximately 80 percent of couples will conceive.

●12 months – In the first 12 months, approximately 85 percent will conceive.

●36 months – Over the next 36 months, approximately 50 percent of remaining couples will go on to conceive spontaneously [9].

●48 months – The 5 to 7 percent of couples who have not conceived after 48 months of attempted conception will only occasionally go on to achieve a spontaneous conception.

Criteria for initiating an infertility evaluation vary depending on personal characteristics (eg, age) and are discussed separately.

●(See "Female infertility: Evaluation".)

●(See "Approach to the male with infertility".)

When is the fertile period of the menstrual cycle? — The fertile interval in each menstrual cycle is approximately six days (figure 2) and includes the five days prior to ovulation plus the day of ovulation (figure 3) [10]. The duration of the fertile period is not affected by age but can vary among women [11]. The highest probability of conception occurs when intercourse takes place one to two days prior to ovulation and on the day of ovulation [10,12-17]. (See "Normal menstrual cycle".)

How do I know if I am in my fertile period? — Multiple options exist for tracking the menstrual cycle and resultant physiologic changes to understand when ovulation is most likely to occur. Studies that establish the efficacy of these methods compared with no intervention or that directly compare these methods are generally lacking. Conversely, some individuals use the methods below to avoid having intercourse during their fertile interval and thus avoid conception. (See "Fertility awareness-based methods of pregnancy prevention".)

●Low-resource interventions – These methods involve minimal cost and equipment. The time required for patient education can be a barrier to use.

•Menstrual calendar – A menstrual calendar involves tracking the days of menses to help predict days of likely ovulation (figure 4). (See "Evaluation of the menstrual cycle and timing of ovulation", section on 'Menstrual cycle charting'.)

•Tracking cervical mucous changes– Changes in cervical mucus can help predict ovulation; the highest probability of conception is on the day of peak production of slippery clear mucus. In a descriptive study of 22 women aged 18 to 39 years, 32 percent reported being "very to extremely" comfortable performing cervical mucous observation [18].

•Basal body temperature measurements – Daily monitoring with a basal-body thermometer can detect the transient increase in body temperature that occurs after ovulation. (See "Evaluation of the menstrual cycle and timing of ovulation", section on 'Basal body temperature monitoring'.)

●Commercially available methods – The interventions below are considered higher-resource because they involve more cost and/or equipment (ie, computer, smart phone) compared with the low-resource interventions above (table 1).

•Luteinizing hormone (LH kits) – Women can attempt to predict the time of ovulation by using a kit to measure urinary luteinizing hormone (LH). Use of a home ovulation test kit may decrease the time to conception [19], particularly in women with irregular cycles or couples who have sexual intercourse infrequently. However, for most women, there is no substantial evidence that self-monitoring to predict ovulation increases cycle fecundability [20,21]. (See "Evaluation of the menstrual cycle and timing of ovulation", section on 'Measurement of LH surge and estradiol rise'.)

-Computer and phone applications (apps) – A novel approach to the issue of coital timing for reproduction involves the use of a mobile application (ie, app). A study of one proprietary app analyzed data from over 200,000 menstrual cycles and nearly 100,000 women to determine the probability of pregnancy in the periovulatory period [22]. The day-specific probability of pregnancy in relation to ovulation was 27, 33, 42, 20, and 8 percent for -3, -2, -1 days prior to ovulation, day of ovulation, and +1 days, respectively. The use of fertility apps to either time or avoid conception is presented in detail elsewhere. (See "Fertility awareness-based methods of pregnancy prevention", section on 'Computer and phone applications (apps)'.)

How often should I have sex? — The highest pregnancy rates occur in couples who have vaginal intercourse every one to two days (in the follicular phase (figure 2)) [12,23-25], but regular intercourse two to three times per week beginning soon after cessation of menses should ensure that intercourse falls within the fertile period and semen quality is optimal [26]. Most data indicate that optimum semen quality, measured in terms of motility, morphology, and total sperm count, occurs when there are two to three days of ejaculatory abstinence; longer intervals are associated with lower pregnancy rates [27].

Effect of lubricants — Some lubricants inhibit sperm motility in vitro (eg, KY jelly, Astroglide, Touch, Replens, olive oil, saliva, KY Sensitive, KY Warming, KY Tingling) [28-33]; however, a secondary analysis of couples in a prospective time-to-pregnancy study found no difference in fecundability between those who used and did not use lubricants (primarily Astroglide, KY Jelly, or Pre-seed) [34]. Although there are no compelling data to suggest that lubricant use impairs fertility, the use of lubricants that do not inhibit sperm motility, such as mineral oil, canola oil, mustard oil, or hydroxyethylcellulose-base (Pre-Seed), is prudent when lubricants are needed.

Coital factors that do not affect fertility — Coital position, presence or absence of female orgasm, and female position (eg, remaining supine) after male ejaculation do not appear to affect the likelihood of conception [20].

How does age affect fertility? — Delayed childbearing can decrease the probability of successful conception and should be taken into account in family and career planning. Women in their late 30s are approximately 40 percent less fertile than women in their early 20s. (See "Effects of advanced maternal age on pregnancy".)

The probability of conception is highly dependent upon maternal age, but paternal age also plays a minor role, especially after age 50 years [35]. In a large well-designed study, the probability of clinical pregnancy following intercourse on the most fertile day of the cycle in women of assumed fertility aged 19 to 26 years, 27 to 34 years, and 35 to 39 years was approximately 50, 40, and 30 percent, respectively, if the male partner was the same age, but 45, 40, and 15 percent, respectively, if he was five years older [36].

●(See "Effect of advanced paternal age on fertility and pregnancy".)

●(See "Effect of advanced paternal age on fertility and pregnancy".)

Environmental factors — Environmental pollutants and toxicants, such as dry cleaning solvents, heavy metals, pesticides, and possibly bisphenol A (BPA) can have adverse effects on fertility and pregnancy. (See "Overview of occupational and environmental risks to reproduction in females".)

A review of studies on sauna bathing concluded that this activity does not influence fertility in women or men [37]. Although hormonal changes occur during sauna bathing, the changes are transient.

EFFECT OF SPECIFIC FACTORS ON FERTILITY

There are no large-scale, randomized, clinical trials examining the effect of lifestyle issues such as cigarette smoking, body mass index (BMI), stress, or alcohol and caffeine consumption on fertility. Most studies are observational and subject to many potential biases. As an example, numerous investigators have reported that primary tubal infertility is increased in women who report a history of many sexual partners, an earlier age at first intercourse, and cigarette smoking. However, women with more sexual partners and an earlier age at first intercourse may also be more likely to smoke cigarettes; thus, it is often difficult to definitively determine if cigarette smoking is an independent contributor to infertility or whether cigarette smoking is largely associated with infertility through other exposures, such as sexually transmitted infections [38,39]. In addition, women who smoke cigarettes tend to consume more alcohol and caffeine than women who do not smoke. This raises the possibility that the relationship between cigarette smoking and reduced fertility may influence observations of an association between alcohol and caffeine consumption and diminished fertility.

In many of the studies discussed below, attempts were made to control for some of the potential confounding interactions through the use of logistic regression and multivariate analyses. However, the absence of data from randomized trials is a major weakness of the evidence in this area. An additional limitation is that there is no biomarker that can be measured to indicate the potential for human conception [40].

Overweight and obesity — Both overweight (25.0 to 29.9 kg/m²) and obese (≥30 kg/m²) body mass indexes (BMIs) have been associated with decreased fertility as well as other adverse effects on health [41]. The effect of BMI on male fertility is unclear. A BMI of 18.5 to 25 kg/m² is associated with little or no increased health risks and, for this reason, is desirable for both females and males irrespective of fertility issues. (See "Overweight and obesity in adults: Health consequences".)

Effect on fertility

Female partner

●Elevated body mass index (BMI) – Both overweight (25.0 to 29.9 kg/m²) and obese (≥30 kg/m²) BMIs have been associated with decreased fertility [41].

●Time to pregnancy and pregnancy rates – Obesity in childhood contributes to menstrual cycle abnormalities and infertility [42]. A cross-sectional study in the United States reported that adolescents who self-reported being obese (BMI >30 kg/m²) were more than twice as likely to remain childless than normal-weight adolescents after adjusting for confounding variables such as adult BMI, nongestational amenorrhea, marital status, ethnicity, geographical location, and socioeconomic status [43]. Even in regularly ovulating women, increasing obesity appears to be associated with decreasing spontaneous pregnancy rates and increased time to pregnancy [44-46]. In addition to absolute body weight, weight gain in adulthood may also increase the amount of time needed to conceive, irrespective of baseline weight or menstrual cyclicity. As an example, a prospective cohort study of nearly 2000 women reported that every 5 kg body weight increase (from the patient's baseline weight at age 18) was associated with a 5 percent increase in the mean duration of time needed for attempted conception (95% CI 3-7 percent) [47]. Of note, approximately 90 percent of the women in this study had regular menstrual cycles which suggests that altered ovulation was not the mechanism. Therefore, women who wish to conceive are counseled about the importance of achieving and maintaining a normal weight.

•Ovulatory dysfunction – Most studies in adults report a BMI greater than 27 kg/m² or a BMI less than 17 kg/m² is associated with increased ovulatory dysfunction and resultant infertility [48-50].

•Metabolic changes – For women with an elevated BMI, subfertility appears to be related to insulin resistance leading to insulin excess [51]. Hyperinsulinemia may lead to androgen excess by reducing sex-hormone-binding globulin synthesis, thereby increasing free testosterone, and by stimulating ovarian androgen production rates. Excess androgen, in turn, is a major factor leading to altered hypothalamic-pituitary and ovarian physiology and anovulation. Obesity-associated hyperleptinemia may be an additional factor in anovulation, not only through the induction of insulin resistance, but also through direct impairment of ovarian function. Factors other than anovulation also likely play a role in obesity-related subfertility [52]. (See "Diagnosis of polycystic ovary syndrome in adults".)

●Weight loss – Prior observational studies have reported both nonsurgical [53-55] and surgical [56-62] weight loss increased the frequency of ovulation and natural conception. However, weight reduction does not appear to be associated with increased fecundability or live birth rate [63-65]. A large, multicenter trial of obese (BMI ≥29 kg/m²) and infertile women reported no difference in birth rates of term singletons or overall live birth rates among women who received a six-month structured weight-loss intervention prior to infertility treatment and control women who went directly to infertility treatment [64]. There were also no differences in the obstetric outcomes of gestational diabetes or hypertensive disorders of pregnancy between intervention and control groups. In the trial, women in the intervention group were more likely to conceive spontaneously (26 versus 16 percent) and underwent fewer fertility treatment cycles (679 versus 1067 treatment cycles) compared with the control women. Study limitations include that target weight loss was reached by only 38 percent of women in the intervention group and the intervention discontinuation rate was 22 percent. It is not known if greater weight reduction per person, increased proportion of women reaching target weight loss, or increased patient continuation rates would increase fecundability.

We continue to advise weight loss for infertile women with an elevated BMI because weight reduction aids in spontaneous conception in some studies and reduces the need for fertility treatment, in addition to providing long-term benefits for overall health [53,55]. In a study of 67 women who had an average weight loss of 10 kg over six months, spontaneous ovulatory cycles resumed in nearly 90 percent (60 of 67), with 52 women becoming pregnant and 45 having a live birth. None of the control patients, consisting of study drop-outs, resumed ovulatory cycles or conceived. One lifestyle modification to achieve weight loss includes increased moderate physical activity, such as walking 150 minutes weekly [66,67]. Dietary intake should be decreased by 500 to 1000 cal/day, which will result in a 1 to 2 pound weekly weight loss. Consuming a low-calorie diet of 1000 to 2000 kcal/day should result in a 10 percent decrease in BMI over six months [68]. Maintaining a 10 percent weight loss with lifestyle modification is uncommon and only achieved by 20 percent after one year [69]. Those participating in a lifestyle moderation program may have an improved chance of maintaining weight reduction as compared with those not in a structural program [70]. (See "Obesity in adults: Overview of management".)

Male partner — The impact of the male partner's BMI on fertility has not been examined extensively. Some observational and animal data suggest an association between increasing male BMI and lower pregnancy rates [71-73]. There is consistent evidence that obesity affects reproductive hormone levels, but studies have reported conflicting results on the effect of obesity on semen parameters [74-77]. An observational study of nearly 4000 sperm donors in China, with an average of eight repeated semen measures per donor, reported that being underweight (BMI <18.5 kg/m²) was associated with lower sperm concentration, total sperm number, and total motile sperm count while being overweight (BMI 25.0 to 29.9 kg/m²) was associated with lower semen volume, total sperm number, and total motile sperm count [78]. The study controlled for age, ethnicity, education, smoking status, marital status, abstinence period, and season. Only 1 percent (n = 38) of the study population were obese (BMI ≥30 kg/m²), which limited the study's ability to identify statistical significance at this weight level. While weight reduction can correct the hormonal imbalance, the effect of weight loss on semen parameters and pregnancy rate has not been studied.

Effect of obesity on fertility therapy — Some studies report poorer outcomes of infertility treatment in obese females (eg, insufficient follicular development, lower oocyte counts, lower fertilization rates) [79-83], while others report outcomes are comparable to nonobese females, but higher doses of ovulation inducing agents need to be used [84-87]. The risk of unsuccessful IVF increases with increasing BMI and may be related to poor oocyte quality, ovarian function, endometrial quality, or a combination of these factors. In a systematic review and meta-analysis including 33 studies and almost 48,000 IVF/ICSI treatment cycles, women who were overweight or obese (BMI ≥25 kg/m²) had a statistically significant small reduction in clinical pregnancy rate (RR 0.90) and live birth rate (RR 0.84) and a significantly higher miscarriage rate (RR 1.31) than normal weight women (BMI <25 kg/m²) [88].

●(See "In vitro fertilization: Overview of clinical issues and questions", section on 'Minimal or unclear effect'.)

Spontaneous abortion — Most studies report an increased spontaneous abortion (SAB) rate in obese women undergoing ART [87-95]. A meta-analysis of 33 studies reported a slightly higher SAB rate (RR 1.31) in women with a BMI >25 kg/m² compared with those with a BMI <25 kg/m² (90 g). An increased risk for pregnancy loss was also noted in those with a BMI >25 kg/m² following single fresh (OR 2.7, 95% CI 1.5-4.9) or frozen blastocyst transfer [94].

Healthy lifestyle

Diet — In healthy couples, there is no strong evidence that dietary variations such as vegetarian diets, low-fat diets, and vitamin or antioxidant-enriched diets improve fertility [20,96]. However, undiagnosed/untreated celiac disease may cause female or male subfertility, which resolves by adopting a gluten-free diet. (See "Epidemiology, pathogenesis, and clinical manifestations of celiac disease in adults".)

●Female partner – Data on the relationship between diet and fertility in women are from observational studies. One of the largest of these studies was a prospective cohort study of over 18,000 married, premenopausal women without a history of infertility who attempted pregnancy or became pregnant [97-102]. Based on their own data and that from other studies, the authors considered the following dietary habits components of a "fertility diet": higher monounsaturated to trans-fat ratio, high percentage of protein from vegetable rather than animal sources, low glycemic index carbohydrates, high fat dairy foods, and use of iron and multivitamin supplements. Healthy women whose diet reflected this composition had a significantly reduced risk of ovulatory disorder infertility. They hypothesized that this diet was favorable to glucose homeostasis and insulin sensitivity, factors that play a role in ovulatory function. The results were based on dietary recall, and thus were subject to recall bias. Other smaller observational studies have supported the beneficial effects of a Mediterranean diet, reduced trans-fat intake, and increased omega-3 fatty acid intake on achieving natural or assisted conception [103-106]. There is no harm to such diets, but no strong data at this time to recommend dietary changes solely for enhancement of fertility.

●Male partner – Observational studies in men have reported improved semen parameters among men with healthy dietary habits; pregnancy rates were not evaluated [107-109].

Caffeine — Female fertility does not appear to be affected by caffeine intake less than 200 mg per day, even for women undergoing IVF therapy [110,111]. A cohort study of over 1700 couples undergoing fertility treatment reported a higher chance of a live birth among women consuming 1 to 5 cups of coffee per day compared with a relevant non-coffee drinking cohort (adjusted relative risk 1.53, 95% CI 1.06-2.21) [112]. Therefore, women contemplating pregnancy probably can have one or two 6 to 8 ounce cups of coffee per day without negatively impacting their ability to conceive (table 2). The impact of caffeine consumption on fertility and reproductive outcomes is presented in detail elsewhere. (See "Caffeine: Effects on reproductive outcomes in females".)

There is no strong evidence to support limiting caffeine intake in the male partner.

Exercise — Female fertility can be adversely affected by increased intensity and duration of exercise. For this reason, we suggest women with BMI <25 kg/m² who are attempting to conceive limit vigorous exercise to fewer than five hours per week. Male fertility does not appear to be affected by exercise.

Female partner — The intensity and duration of exercise can affect female fertility, but the specific type of exercise does not appear to be a factor. In some epidemiological studies, vigorous/intense physical activity was associated with ovulatory infertility [113,114], while others have not observed a significant association [100]. Baseline patient characteristics appear to play a role. In a well-designed study of Danish women, vigorous physical activity (running, fast cycling, aerobics, swimming, gymnastics) was associated with a reduction in fecundity; however, the effect was confined to women with a BMI <25 kg/m²; there was a slightly positive effect of all levels of exercise among overweight and obese women [115]. In women undergoing IVF, another study noted that ≥4 hours of strenuous exercise weekly over a period of years was associated with poorer outcomes [116].

The effects of strenuous exercise on fertility could be related to (1) reduced progesterone production during the luteal phase of the menstrual cycle in ovulatory women (ie, luteal phase defect), (2) alterations in GnRH production, LH and FSH secretion, and estradiol production and metabolism, resulting in anovulation, or (3) changes in leptin levels [117-119]. Other factors may include decreased body fat and changes in diet, such as an increase in fiber and a decrease in fat intake, in women who exercise strenuously. (See "Functional hypothalamic amenorrhea: Pathophysiology and clinical manifestations".)

However, from a population perspective, inadequate levels of exercise associated with obesity may be a more common cause of anovulation and subsequent infertility than exercise-associated anovulation [120,121]. (See 'Overweight and obesity' above.)

Male partner — The relationship between fertility and exercise in the male has not been well characterized. One large retrospective study examined the association between regular physical exercise and semen quality in 2261 men whose partners were undergoing IVF [122]. Overall, none of the semen parameters studied was affected by exercise; however, men who bicycled ≥5 hours/week demonstrated lower sperm concentrations and lower numbers of total motile sperm than their non-exercising counterparts; pregnancy rates were not evaluated. Results were not influenced by age, BMI or a history of male infertility.

Stress and stress reduction — Many observational studies have suggested that stress is associated with infertility and, in turn, the diagnosis and treatment of infertility clearly can be stressful. No clinical trial has demonstrated definitively that reducing stress prior to infertility treatment improves pregnancy rates. (See "Psychological stress and infertility".)

●Impact of stress on assisted reproductive outcomes – In a 2011 meta-analysis that pooled 31 prospective trials examining the association between stress, distress in female patients, and assisted reproductive technology (ART) outcomes, small but statistically significant negative correlations were observed between ART outcomes and stress and anxiety [123]. Importantly, however, the association with anxiety disappeared when live birth rates were examined, and too few trials using stress were included to allow statistical analysis.

●Impact of stress reduction – A 2021 meta-analysis of 15 trials evaluating the impact of psychosocial interventions for individuals undergoing assisted reproductive technology reported a small but significant increase in live birth rate with psychosocial interventions, particularly long-term and mind-body interventions (risk ratio 1.21, 95% CI 1.04-1.43 and risk ratio 1.25, 95% CI 1.00-1.55, respectively) [124]

Substance use

Tobacco — Use of tobacco by the female partner, and possibly by the male partner, has been associated with subfertility, and may account for as much as 13 percent of cases [125]. Observational studies suggest that much of the subfertility associated with smoking can be reversed within a year of cessation [126-129].

Given the multiple health risks associated with cigarette smoking, cessation should be encouraged irrespective of fertility and pregnancy issues. (See "Benefits and consequences of smoking cessation" and "Overview of smoking cessation management in adults".)

Female partner — Studies of the impact of smoking on fertility have typically analyzed the effects of "cigarettes smoked per day" on fecundability. Most series report that fecundability is decreased if the female partner smokes more than 10 cigarettes per day. In a 1998 meta-analysis including data from almost 11,000 smoking women and over 19,000 nonsmokers, cigarette smoking by the female partner was associated with a statistically significant increase in infertility compared with nonsmokers (odds ratio [OR] 1.60, 95% CI 1.34-1.91) [130]. Although only observational studies were included, the evidence was compelling because of the consistency of the effect across different study designs, sample sizes, and types of outcome. Others have reported that the time to achieve pregnancy increases with the number of cigarettes smoked per day (figure 5) [131].

An additional concern is that subfertility in smokers cannot necessarily be overcome by assisted reproductive technology (ART). The same 1998 meta-analysis found that the odds of pregnancy per number of in vitro fertilization (IVF) cycles was significantly lower in smokers compared with nonsmokers (OR 0.66, 95% CI 0.49-0.88) [130].

Possible mechanisms for subfertility in smokers include adverse tubal and/or cervical changes, damage to gametes, and increase in spontaneous abortion and ectopic pregnancies [39,132]. Numerous studies linking smoking to early menopause suggest that cigarette smoking causes premature depletion of the ovarian pool of oocytes and premature aging of the ovary by one to four years [133,134]; this decrease in ovarian reserve can account for the subfertility observed in smokers.

Components of cigarette smoke may cause oxidative stress and DNA damage to the ovarian follicle [135,136]. For this reason, smoking by a pregnant woman may be harmful to the ovaries of her fetus [137]. In a study of the effect of in-utero exposure to cigarette smoke on the fertility of the female partner, fecundability was reduced among women exposed to cigarette smoke in-utero (fecundability ratio 0.5, 95% CI 0.4-0.8) [138]. This association was present after adjusting for age of the female partner, frequency of intercourse, current smoking status, age at menarche, childhood exposure to cigarette smoke, body mass of the female partner, alcohol and caffeine consumption, educational level, and reproductive history. There may also be adverse reproductive effects of maternal smoking on male fetuses. An epidemiologic study reported that adult male offspring of mothers who smoked more than 10 cigarettes/day during pregnancy had lower sperm counts than the sons of nonsmokers [139].

Male partner — Dose-dependent decreases in semen quality have been observed in men who smoke, but available evidence does not prove that smoking decreases male fertility. An analysis of 27 epidemiologic studies addressing the effect of smoking on sperm concentration, motility, and morphology in fertile and infertile men found a modest reduction in semen quality and altered hormone levels among smokers compared with nonsmokers, but did not find a reduction in male fertility associated with paternal smoking [140]. Fertile male smokers had a 23 percent decrease in sperm concentration and a 13 percent decrease in sperm motility compared with fertile male nonsmokers.

A deleterious effect on male fertility or a secondary deleterious effect on female fertility cannot be definitively excluded, especially among men with marginal semen quality. Studies in subfertile populations that evaluated the effect of smoking by the male partner on the success rate of IVF and intracytoplasmic sperm injection (ICSI) have reported a significant decrease in the number of pregnancies achieved [141,142].

Alcohol intake — Moderate alcohol consumption <2 drinks/day (1 drink = 10 g of ethanol) probably has no or minimal adverse effects on fertility, but higher levels of alcohol consumption should probably be avoided when attempting pregnancy [20,143-146]. Abstinence at conception and during pregnancy is generally recommended because a safe level of prenatal alcohol consumption has not been established. In both men and women, the dose-response relationship between alcohol intake and fertility requires additional study.

Female partner — Most observational studies have reported moderate and heavy female drinkers tend to take longer to achieve a pregnancy and are at higher risk of undergoing an infertility evaluation [144,145,147-149]. Others have not noted an adverse effect of moderate alcohol intake on fertility [150,151] nor a difference in risk of ovulatory dysfunction between women with high versus low alcohol intake [152]. Heavy alcohol intake is typically defined as ≥14 drinks per week, and moderate intake is usually defined as 3 to 13 drinks per week, but these definitions are arbitrary and vary in different studies. However, alcohol consumption can impact the developing fetus. (See "Alcohol intake and pregnancy".)

Moderate alcohol use may affect success rates of women undergoing IVF, but the supporting data are mixed. A retrospective study on alcohol consumption reported that women who drank at least four drinks per week were at 16 percent less odds of a live birth after IVF compared with women who had fewer drinks (OR 0.84, CI 0.71-0.99) [153]. By contrast, a prospective study of 300 women undergoing IVF failed to find an association between alcohol conception and live birth. The authors divided their subjects corresponding to <0.5 glass of alcohol/day, 0.5 to 1 glass/day, 1 to 2 glasses/day, and >2 glasses per day. No difference in live births was observed [110]. A Danish cohort study involving over 1700 women and their partners who underwent intrauterine insemination, IVF, or ICSI treatment failed to demonstrate an effect of alcohol consumption on any of the three treatment modalities for 1 to 2, 3 to 7, and >7 drinks per week. For the IVF/ICSI groups, the adjusted relative risk of achieving live birth was 1.00 (95% CI 0.83-1.21), 0.95 (95% CI 0.75-1.20), and 0.89 (95% CI 0.53-1.51) for 1 to 2, 3 to 7, and >7 drinks per week, respectively, compared with a nondrinking cohort [154].

Male partner — Heavy alcohol use by the male partner is related to abnormalities in gonadal function, including reduced testosterone production, impotence, and decreased spermatogenesis [155-157]. In the IVF study cited above [153], in couples in which both partners consumed at least four drinks per week, the odds of a live birth were diminished by 21 percent compared with couples in which both partners drank less than four or more drinks per week. For patients with a live birth, a meta-analysis of 55 studies reported paternal alcohol use prior to conception was associated with an increased risk of total congenital heart defects in the offspring (OR 1.44, 95% CI 1.19-1.74) [158].

Other drugs — There are minimal data on the effects of recreational drug use on fertility [159]. A study of self-reported marijuana use by individuals undergoing fertility treatment reported a higher risk of pregnancy loss in marijuana smokers compared with past or never-users (n = 308, 379 cycles, adjusted probability 54 versus 26 percent) [160]. Unexpectedly, a higher pregnancy rate was reported for couples undergoing IVF when the male partner smoked marijuana while the female partner did not. These drugs should be avoided because of their general health risks.

●(See "Substance use during pregnancy: Screening and prenatal care".)

●(See "Substance use during pregnancy: Overview of selected drugs".)

LIFESTYLE EFFECTS ON ESTABLISHED PREGNANCY — Cigarette smoking, obesity, alcohol and caffeine consumption, and recreational drug use can have a significant adverse impact on pregnancy and fetal outcomes. The combined impact of these exposures on both fertility and pregnancy outcome emphasizes the importance of lifestyle interventions for the couple planning a pregnancy. (See "The preconception office visit".)

●(See "Obesity in pregnancy: Complications and maternal management".)

●(See "Caffeine: Effects on reproductive outcomes in females".)

●(See "Cigarette and tobacco products in pregnancy: Impact on pregnancy and the neonate".)

●(See "Alcohol intake and pregnancy" and "Neonatal abstinence syndrome (NAS): Clinical features and diagnosis".)

●(See "Substance use during pregnancy: Screening and prenatal care".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Female infertility".)

SUMMARY AND RECOMMENDATIONS — Lifestyle factors can affect the duration of time before achieving pregnancy and modifying these factors may enhance fertility. The recommendations below are based upon data from observational studies; no randomized trials have been performed.

●Couples should be informed that delayed childbearing, especially after age 30 years, can decrease the probability of successful conception, and they should take this into account in family and career planning. (See 'How does age affect fertility?' above.)

●We suggest sexual intercourse two to three times per week from soon after cessation of menses through the day of ovulation to ensure that intercourse falls within the most fertile period (up to two days before ovulation) and semen quality is optimal (Grade 2C). (See 'When is the fertile period of the menstrual cycle?' above.)

●We recommend smoking cessation for couples who smoke based on the overall health benefits of smoking cessation (Grade 1A). Use of tobacco by the female partner, and possibly the male partner, appears to be associated with subfertility. For couples planning pregnancy, observational studies suggest fertility is enhanced when use of tobacco products is terminated. (See 'Tobacco' above.)

●A body mass index (BMI) greater than 27 kg/m² or less than 17 kg/m² is associated with an increased risk of anovulatory infertility. The former is often related to polycystic ovary syndrome and the latter is often related to amenorrhea caused by excessive exercise or poor caloric intake (eg, eating disorders). We suggest couples try to achieve a BMI of 18.5 to 25 kg/m² (Grade 2C). Women in this weight range are less likely to have ovulatory dysfunction than women at either extreme of BMI. This range is associated with little or no increased health risks and, for this reason, is desirable for both women and men. There is little information on the relationship between male fertility and BMI. (See 'Overweight and obesity' above.)

●Moderate and heavy female drinkers tend to take longer to achieve a pregnancy and are at higher risk of undergoing an infertility evaluation. We suggest that women who are attempting to conceive avoid all alcohol, given a safe level of prenatal alcohol consumption with respect to the fetus has not been determined (Grade 2C). Moderate alcohol intake by the male partner does not appear to be associated with decreased fertility. (See 'Alcohol intake' above.)

●It is unclear whether high caffeine consumption affects female fertility; it does not appear to affect male fertility. We suggest women contemplating pregnancy limit caffeine intake to no more than one or two cups of coffee per day (total of 200 mg caffeine) (Grade 2C). (See 'Caffeine' above.)