This review states that it "disproves the suggestion by Shettles and Billings that the selection of male offspring by intercourse around the time of ovulation is possible." It also reports a small but statistically significant deficit of male births during the most fertile period, with the deficit associated primarily with conception 2–0 days before ovulation.

Among 221 women who became pregnant, conception occurred only when intercourse took place during a 6-day period that ended on the estimated day of ovulation. The probability of conception ranged from 0.10 when intercourse occurred 5 days before ovulation to 0.33 when it occurred on the day of ovulation itself. Cycles producing male and female babies had similar patterns of intercourse in relation to ovulation. For practical purposes, the timing of sexual intercourse in relation to ovulation has no influence on the sex of the baby.

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.

In this prospective study of 221 healthy women trying to conceive, the authors examined day-specific probabilities of conception and also whether intercourse timing affected the sex of the baby. They report: "The timing of intercourse may also be associated with the sex of the baby." However, in the conclusions they state: "For practical purposes, the timing of sexual intercourse in relation to ovulation has no influence on the sex of the baby." They also note that nearly all pregnancies resulted from intercourse during the 6‑day period ending on the day of ovulation, but without consistent variation in sex ratio by day.

BACKGROUND: The timing of sexual intercourse in relation to ovulation strongly influences the chance of conception, although the actual number of fertile days in a woman's menstrual cycle is uncertain. The timing of intercourse may also be associated with the sex of the baby. CONCLUSIONS: Among healthy women trying to conceive, nearly all pregnancies can be attributed to intercourse during a six-day period ending on the day of ovulation. For practical purposes, the timing of sexual intercourse in relation to ovulation has no influence on the sex of the baby.

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.

This earlier observational study investigated the sex ratio of infants in relation to the day of the menstrual cycle when conception occurred. It found that "The proportion of male babies was significantly higher (65.5 +/- 3.9 per cent, mean +/- S.D.) in the offspring of women who resumed intercourse two days after ovulation." It also states: "This proportion tended to be lower on or near the day of ovulation than on the previous one or two days" and concludes that "These results... demonstrate that insemination on different days of the menstrual cycle does lead to variations in sex ratio." The authors caution that couples should not delay intercourse to try to conceive a boy until more is known about possible risks of delayed fertilization.

In this cohort study of 5,283 Dutch women, we examined the relation between waiting time to pregnancy and the sex of offspring. The time taken to get pregnant is positively related to the chance of having a boy in couples conceiving naturally. Each additional year of trying to get pregnant is associated with a nearly 4% higher expected probability of delivering a male baby. The findings are consistent with the hypothesis that more viscous cervical mucus reduces the chance of conception and increases the chance of male offspring, but intercourse timing relative to ovulation was not manipulated as a sex-selection method.

This New England Journal of Medicine article reports: "Among healthy women trying to conceive, nearly all pregnancies can be attributed to intercourse during a six-day period ending on the day of ovulation, and the timing of sexual intercourse in relation to ovulation has no influence on the sex of the baby." The authors further note: "The study suggests that manipulation of the timing of insemination during the cycle cannot be used to affect the sex of offspring."

The results clearly refute the theory that intercourse close to ovulation favors male conceptions. While the findings are consistent with the hypothesis that timing of intercourse in relation to ovulation might influence sex ratio, they provide no evidence that this effect is strong enough or consistent enough to be of practical use in sex preselection.

For most couples, getting pregnant comes down to having sex around the time of ovulation. The window of fertility is about 6 days each cycle. This is because sperm can live in a woman’s body for as long as 5 days, while an egg can survive for about 12 to 24 hours after ovulation. So you can have sex up to 5 days before ovulation or 1 day after and still get pregnant. ACOG does not recommend timing intercourse as a means to choose a baby’s sex and instead focuses on timing only to improve the chances of conception.

The page explains that, according to Shettles, the timing of sexual intercourse within the menstrual cycle has a large impact on the sex of the child. It also notes that a 1979 study in The New England Journal of Medicine found male fetuses were more often produced when intercourse occurred closest to ovulation, while a 1995 NEJM study refuted any association between timing and fetal sex.

Multiple well-designed studies have found no significant relationship between the timing of intercourse in relation to ovulation and the sex of the baby. Research consistently shows that while timing intercourse can influence the probability of conception, it does not reliably affect whether the baby is male or female. The consensus in the scientific literature is that timing of intercourse cannot be used as an effective method for sex selection.

The Whelan Method is a timing-based sex selection method that claims couples can increase the probability of conceiving an infant of the desired sex through timing intercourse. According to Whelan’s method, couples should have intercourse two or three days prior to ovulation to increase their chances of conceiving a female infant, and four to six days before ovulation to increase the probability of conceiving a male infant. However, the article notes: "Since the publication of Whelan’s book, many researchers have refuted her theories regarding the relationship between intercourse timing and an infant’s sex. A study published in The New England Journal of Medicine in 1995 refuted all claims that intercourse timing affects the outcome of an infant’s sex. That study asserted that there was no association between intercourse timing and sex outcome, and that timing of intercourse holds no value in sex selection."

This article says that studies since Shettles's time have shown that timing sex in relation to ovulation does not actually influence whether you conceive a boy or a girl. It also states that there is no medical evidence to suggest couples can influence the baby's sex by timing intercourse.

The article describes the Shettles method as the idea that when and how you have sexual intercourse may influence the sex of your baby. It then notes that a 1991 review of studies refutes Shettles's claims and says more research is needed to fully support the method.

This article reviews scientific evidence on sex selection and timing. It states: "Larger and more recent studies since then have shown that the timing of sexual intercourse with respect to ovulation does not affect the sex of the baby." It further notes that while some small studies from the 1980s and 1990s suggested slight differences, "the latest studies show that the timing of sexual intercourse does not affect the sex of the baby" and that popular timing-based methods such as the Shettles and Babydust methods are not supported by high-quality data.

This official fertility education site explains how timing affects chances of conception, stating that pregnancy is technically only possible if sex occurs during the five days before ovulation or on the day of ovulation, and that the chance is around 30% when sex occurs on the day of ovulation or the two days before. It emphasizes that the fertile window is the day of ovulation and the five days beforehand. The page focuses on probability of becoming pregnant; it does not indicate any clinically useful effect of intercourse timing on the sex of the baby, implying that timing is recommended to maximize conception chances rather than to alter sex ratio.

The so-called Shettles method claims that timing intercourse close to ovulation favors boys and earlier in the fertile window favors girls. However, large prospective studies that carefully measured ovulation and tracked intercourse have not supported a strong or reliable effect of timing on sex ratio. Evidence indicates that timing of coitus relative to ovulation influences the chance of conception but does not provide a practical way for couples to choose a baby’s sex.

In conclusion, our data from 68 women using effective methods of birth control show that intercourse is most likely to occur during the 6 fertile days of the menstrual cycle, defined as the 5 days before ovulation and the day of ovulation itself. These findings confirm that timing of intercourse in relation to ovulation is crucial for conception, but they do not demonstrate any effect of this timing on the sex of potential offspring.

The article says the Shettles method proposes that timing intercourse as close to ovulation as possible may increase the odds of having a boy, while sex earlier in the fertile window may increase the odds of having a girl. It also states that experts say the method is not scientifically accurate and that studies found no difference in sex ratios or no conclusive evidence supporting it.

The page says that the Shettles method recommends intercourse as close to ovulation as possible to conceive a boy and 2–3 days before ovulation to conceive a girl. It also states that scientific research does not support timed-intercourse methods as a reliable way to choose a baby's sex and cites a 1995 study finding no reliable link between intercourse timing and sex.

This commercial fertility site describes the Shettles method and related timing strategies, recommending intercourse near ovulation to conceive a boy and several days before ovulation to conceive a girl. However, it acknowledges that many medical professionals are skeptical: "While the theory behind the Shettles method appears, prima facie, fairly logical, there are still many medical professionals who suggest there is no sure way to influence the gender of your child" other than lab methods such as sperm sorting. It also cautions that trying to influence sex by restricting intercourse to specific days may decrease the overall chance of conceiving in a given cycle.

In this educational video, the presenter summarizes data from a major study on timing of intercourse and conception, giving day‑specific conception probabilities: for example, about 8% five days before ovulation, rising to 33% on the day of ovulation, and noting no conceptions on days after ovulation. She explicitly states that the researchers found that nearly all pregnancies occurred within the six days leading up to and including ovulation. She also reports that the study "found no scientific support of the day of intercourse predicting the sex of the baby, whether it was a boy or a girl," indicating that intercourse timing affected whether conception occurred, but not the baby’s sex.

Mainstream obstetrics and fertility guidance generally treats the Shettles method as unproven, and randomized or well-controlled studies have not established a reliable effect of intercourse timing relative to ovulation on a baby's sex. Claims that timing can meaningfully select boy versus girl are not supported by accepted clinical evidence.

The article explains the Shettles timing theory: intercourse on the day of ovulation and the following two to three days for a boy, and intercourse after menstruation until about three days before ovulation for a girl. It also says there is no real evidence proving the method works and that the evidence is anecdotal.