The Pearl Index is determined by the number of unwanted pregnancies associated with 100 women. For example, 100 women can use a particular contraceptive for 1 year at a time using the method to be examined. If three pregnancies occur in this group during this period, the Pearl index is 3.0. LNG IUS was first studied in the 1970s. It was approved in Finland in September 1990 and FDA approval was granted in 2000. About 12% of married women of childbearing age used an IUD. A total of 106 million women used an IUD. The highest utilization rates are in China and the lowest in North America. IUS LNG is now available in the United States and more than 120 countries and has been used by more than 4 million women.

It has high contraceptive efficacy. The LNG SIU provides a reversible contraceptive with a cumulative crude pregnancy rate of 0.0% to 0.5% for 5 years or a Pearl Index pregnancy rate of 0.0% to 0.2% for 7 years. The real-life index takes into account all the factors that can reduce the effectiveness of a particular birth control method as follows: Like all birth control measures, the pearl index is a calculation based on the observations of a particular sample population. Therefore, studies of different populations using the same contraceptive give different values for the index. The culture and demography of the population studied and the teaching technique used to teach the method have a significant impact on their failure rate. [2] [3] The Pearl Index is sometimes used as a statistical estimate of the number of unintended pregnancies in the exposure years of 100 women (e.g., 100 women over one year of age or 10 women over 10 years of age). It is also sometimes used to compare contraceptive methods, with a lower Pearl index giving a lower chance of getting pregnant unintentionally. Testosterone enanthate (TE) is an esterified version of testosterone with a half-life of 4.5 days. In comparison, unmodified T has a half-life of 10 min (Nieschlag et al., 2012).

TE has been used for many years as a T replacement for low-dim men with a good safety profile. After numerous small studies showing the effectiveness of TE administered as intramuscular (IM) injections to suppress sperm production at very low levels (Patanelli, 1978), TE was used in a multicenter contraceptive efficacy study in which men received weekly IM injections of TE 200 mg for 12 months after confirmation of azoospermia. Of 271 fertile and healthy men, 157 completed the suppression phase of the study and became azoospermic. The average latency at azoospermia was about 120 days. During the efficacy phase, only one pregnancy was observed after 1486 months of cumulative exposure in 119 couples, resulting in a Pearl index of 0.8 per 100 person-years (95% CI: 0.02-4.5) (World Health Organization Working Group on Methods for Regulating Male Fertility, 1990). The Pearl Index is a commonly used measure of contraceptive effectiveness, calculated based on the number of pregnancies, the number of couples at risk of pregnancy, and when they use the method. For comparison, Pearl indices for oral contraceptives marketed to women range from 0.29 to 2.86 per 100 person-years (Trussell and Portman, 2013). The favorable results of this study on azoospermia led to a second multicenter international study in which men with oligozoospermia (originally arbitrarily defined as ≤ 5 million /ml of ejaculate) were allowed to enter the efficacy phase. Out of 399 pairs, 349 completed the suppression phase and showed sperm concentrations of ≤ 5 million/ml.

These couples entered the efficacy phase and more than 180 person-years of exposure, 5 pregnancies were observed. Since three of the pregnancies occurred in couples where the male sperm concentration was > 4 million/ml, the threshold for entry into the efficacy phase was reduced to ≤ 3 million/ml. After this change in admission criteria for 49.5 person-years, the study identified 4 pregnancies, none of which occurred in men with azoospermia. The average latency time to reach the revised definition of oligozoospermia (≤ 3 million/ml) was 68 days. The total Pearl index for the study was 1.4 (95% CI: 0.4-3.7) per 100 person-years, which was comparable to hormonal contraceptive methods used by women. The median time to restore normal sperm concentration was 112 days (World Health Organization Working Group on Methods of Regulating Male Fertility, 1996). These proof-of-concept studies showed that hormonal suppression of spermatogenesis up to azoospermia was achievable for nearly 70% of participants and increased above 95% when suppressed at oligozoospermic levels (Table 1). In addition, the removal of these levels ensured the effectiveness of contraception and was reversible at the normal range of sperm concentrations in 98% of participants who completed follow-up. However, this approach had two drawbacks: (1) The unsatisfactory pharmacokinetics of TE injections resulted in highly fluctuating T levels and the need for frequent and weekly injections; (2) High doses of TE were used to induce and maintain adequate suppression of spermatogenesis, resulting in supraphysiological T levels that may have affected the frequency of side effects and overall acceptance of the preparation. Side effects that occurred in these studies were likely to be related to androgens, including acne, weight gain, behavioral effects, reduction of high-density lipoprotein cholesterol (HDL-C), and increased hematopoiesis.

For these reasons, long-acting T esters and other administration strategies were sought. The PI with perfect use was 1.0 pregnancies per 100 years of women and the probability of pregnancy at 13 cycles was 1.0%. These figures make it possible to compare the effectiveness of Natural Cycles with other contraceptives. The definition of perfect use of the app in this study corresponds to what users of the app are asked to do, that is, abstain or practice safe sex on red days. Other studies have calculated comparable yields of FAB methods when supplemented by other methods on fertile days. Frank-Hermann et al. calculated the effectiveness of a sympto-thermal method supplemented with condoms at 0.6 [10], and Arevalo et al. calculated the effectiveness of the TwoDay method at 6.3 when supplemented with a condom or withdrawal [9]. Since we were not sufficiently aware of our users` behavior over time, we were unable to calculate the results of the life table for perfect use. The definition of perfect use that we use in this study will likely lead to an upward biased estimate. Since we have only recorded cycles where we are sure that users have not had unprotected sex on a fertile day, we ignore cycles where users have actually abstained but have not recorded this information.

In practice, we have no other way to estimate the effectiveness of perfect use. An increase in body mass index or weight is a factor that has been postulated to increase OC failure rates. It is well known that obesity rates among adult women have increased significantly in recent decades. According to the National Health and Nutrition Survey, the prevalence of obesity among women ≥ 20 more than doubled, from 15.8% in 1960-1962 to 36.1% in 2009-2010 [23]. Among women aged 20 to 39, the prevalence of obesity increased by almost 20% between 1999 and 2008 (from 28.4% in 1999 to 2000 to 34.0% in 2007 to 2008) [24]. Pregnancy rates are also calculated differently from one study to another. The definition of method failure and user failure may vary, as some studies may exclude pregnancies from classification as user errors if only 1 pill was missed, while others may exclude them even if 3 pills were missed [5]. To obtain a definition of perfect use that provides sufficient statistical accuracy with minimal assumptions, we used an approach similar to Frank-Hermann et al. [10].

We treated certain types of sexual behavior as perfect use, and then correlated all pregnancies that occur during perfect use with all perfect use cycles.