Peri-implantation intercourse does not lower fecundability

The probability of pregnancy in 100 episodes of sexual intercourse: A measure of male contraceptive performance

BACKGROUND

Accurately judging the efficacy of contraceptives is vital for preventing unintended pregnancy. The Pearl index and life table analysis describe female contraceptive performance. However, they are not ideal for quantifying male contraceptive efficacy given differences between male and female methods. In particular, male contraceptives like condoms are used "on demand" rather than long-term like female contraceptives. Additionally, the number of episodes of sexual intercourse, a key determinant of risk, is not considered. Lastly, men can father concurrent pregnancies in more than one woman. For these reasons, a male-specific measure may provide a more accurate measure of male contraceptive efficacy.

OBJECTIVES AND METHODS

As each episode of heterosexual intercourse within a fertile couple is associated with an approximately 3% risk of pregnancy, the chance of an unintended pregnancy with a given number of episodes of sexual intercourse can be modeled with and without contraceptives of various effectiveness.

RESULTS

Such modeling demonstrates that unintended pregnancy is strongly associated with both the number of episodes of sexual intercourse and the efficacy of the method. Based on these models, I propose a novel metric for male contraceptive efficacy called the Probability of Pregnancy100, defined as the percent chance of an unintended pregnancy occurring with 100 episodes of intercourse. Probability of Pregnancy100 should be easy for men to understand and is applicable to men with multiple sexual partners or men using "on-demand" contraceptives.

DISCUSSION AND CONCLUSIONS

The prevention of unintended pregnancy by a male contraceptive is strongly influenced by both method efficacy and sexual frequency. Probability of Pregnancy100 may offer a better measure of male contraceptive efficacy compared to the Pearl index and life table analysis as it takes sexual frequency into account; however, Probability of Pregnancy100 will need to be tested prospectively in male contraceptive studies alongside the Pearl index and life table analysis to determine its utility compared to these existing measures of contraceptive efficacy.

Sperm intrusion into the implantation-stage blastocyst and its potential biological significance

The human embryo derives from fusion of oocyte and sperm, undergoes growth and differentiation, resulting in a blastocyst. To initiate implantation, the blastocyst hatches from the zona pellucida, allowing access from external inputs. Modelling of uterine sperm distribution indicates that 200-5000 sperm cells may reach the implantation-stage blastocyst following natural coitus. We show ultrastructural evidence of sperm cells intruding into trophectoderm cells of zona-free blastocysts obtained from the uterus of rhesus monkeys. Interaction between additional sperm and zona-free blastocyst could be an evolutionary feature yielding adaptive processes influencing the developmental fate of embryos. This process bears potential implications in pregnancy success, sperm competition and human health.

Cultivable vaginal Lactobacillus is not associated with fecundability in Kenyan women attempting to conceive

OBJECTIVE

To examine the association between cultivable vaginal Lactobacillus and fecundability in Kenyan women attempting nonmedically assisted conception.

DESIGN

Prospective preconception cohort.

SETTING

Nairobi and Mombasa, Kenya.

PATIENT(S)

Women trying to conceive who reported ≤3 months of pre-enrollment conception attempt time.

INTERVENTION(S)

Cultivable Lactobacillus (primary), Lactobacillus morphotypes on Gram stain (secondary).

MAIN OUTCOME MEASURE(S)

Participants reported the first day of their last menstrual period and recent sexual behavior, underwent pregnancy testing, and provided vaginal specimen samples for Lactobacillus culture and Gram stain at ≤6 monthly preconception visits. The outcome was fecundability-the per-menstrual cycle probability of pregnancy. Associations between cultivable Lactobacillus and Lactobacillus morphotypes on Gram stain at the visit before each pregnancy test and fecundability were estimated using proportional probabilities models to generate fecundability ratios (FRs).

RESULT(S)

A total of 458 women contributed 1,376 menstrual cycles. At enrollment, 65.3% (n = 299) of participants had cultivable Lactobacillus, 47.4% (n = 217) had cultivable hydrogen peroxide producing Lactobacillus, and 64.6% (n = 296) had Lactobacillus detected on Gram stain. In unadjusted analysis, there was no association between cultivable Lactobacillus at the prior visit and fecundability (FR, 0.92; 95% CI, 0.73-1.16); results were similar after adjustment for age, frequency of condomless sex, and study site (adjusted FR, 0.92; 95% CI, 0.72-1.18). Lactobacillus on Gram stain at the visit prior was associated with modestly higher fecundability (adjusted FR, 1.18; 95% CI, 0.92-1.51).

CONCLUSION(S)

Cultivable Lactobacillus was not associated with fecundability, although Lactobacillus morphotypes detected on Gram stain were somewhat associated with increased fecundability. The relationship between vaginal Lactobacillus and fecundity may be species-specific.