Generally, conception refers to the successful combination of eggs and sperm, with the formation of fertilized eggs, thus it is essential to have sex at the appropriate time. Nevertheless, Lorenz[1-3] found that regular sex in the menstrual cycle, even not during the ovulation period, might increase the chances of conception, the mechanism of which could be that shifts in immunity response caused by sexual activity were conducive to reproductive activities. Accordingly, our researchers explored the role of maintaining the integrity of sexual response cycle in the improvements of ovulation rate and pregnancy outcomes, whose findings indicated that the incidence rate of FSD in experimental group decreased after intervention, with the sexual satisfaction degree, periodic ovulation rate, clinical pregnancy rate, and live birth rate higher than those in the control group, while the biochemical pregnancy rate and abortion rate had no differences.
As is known to all, ovulation function, the quality of ovum, the quality and number of sperm and the patency status of female genital tract are closely related to the success rate of pregnancy [13]. Although it is generally accepted that ovulation occurs spontaneously in female human, which is different from animals such as the rabbits, whose ovulation rely on mating, whether ovulation can be accelerated by coitus remains controversial. For instance, some researchers maintain that a second ovulation can be induced by intercourse after spontaneous ovulation [14]. At present, many studies have reported that the timing and frequency of intercourse relative to ovulation are closely associated with pregnancy [15, 16], lacking of research on the correlation between sexual behavior guidance and ovulation or pregnancy outcomes. On the basis of previous researches, our study found that the periodic ovulation rate and clinical pregnancy rate were significantly higher than those in the control group, with the pre-pregnancy cycle of ovulation monitoring shortened. Moreover, our research revealed that, through observation of cervical mucus under the microscope, it was more likely to found centrally distributed fern-like crystals with typical morphology in the experimental group, while less or no fern-like crystals existed and the glycoprotein distributed in a reticular pattern in the control group (Figure1-2). Accordingly, we hypothesized that sexual behavior could affect the endocrine hormone levels in patients to some extent. Related studies have also suggested that sexual excitement can induce the hypothalamus to secrete gonadotropin-releasing hormone (GnRH) [17]. Combined with the positive feedback effect of estrogen, serum luteinizing hormone (LH) level is easier to reach peak, which is a favorable condition for ovulation.
Currently, with the adjustment and improvement of the fertility policy, the rising problem of infertility is particularly prominent. Furthermore, relevant studies have shown that there is a close association between sex function and conception[18], with the incidence of FSD in infertile women reported by epidemiologic studies up to 87.1% [6], of which the occurrence is closely related to psychosocial factors[19], such as anxiety and depression, which may also lead to dysfunction of the hypothalamic-pituitary-gonadal axis (HPGA), abnormal hormone levels, menstrual disturbance and ovulation disorders. The complete sexual response cycle includes sexual desire phase, sexual arousal phase, sexual plateau phase, sexual orgasm phase and sexual resolution phase. FSD may occur due to obstacles in any phases of female sexual response cycle, while the correlation research indicates that the female sexual desire phase is the first stage as well as an essential link of the sexual response cycle, which can be triggered through touching erogenous zones [20, 21]. In addition, the relevant findings provide evidence that genital stimulation activated widespread brain regions in differential temporal patterns in the approach to, during, and after orgasm [22, 23]. However, some researchers claim that there are no definitive explanations for what triggers orgasm as yet [24]. In our study, the couples in the experimental group who received guidance on sex behavior and psychological counseling were better at overcoming negative emotions, such as anxiety and fear, and effectively stimulating sensitive areas with correct techniques, with the Bartholin's gland promoted to secrete sufficient fluid to lubricate the vagina, which is conducive to achieving sexual arousal or even reaching orgasm.
It's easy to understand that sexual dysfunction will reduce the probability of pregnancy. Furthermore, relevant studies [25, 26] have shown that, sexual excitement and orgasm are of positive significance to improve the clinical pregnancy rate, which is consistent with our findings. Its mechanism may be related to the oxytocin (OT) released by pituitary during orgasm, which has direct effects on female and male sexual behavior [27], and the intensity of orgasm is positively correlated with the concentration of OT in the peripheral blood. Additionally, it has been proved that OT is released by the posterior pituitary during male orgasm, which is supposed to participate in the ejaculatory process [28]. As a neuromodulator, OT plays a crucial role in affecting the brain's cognitive and perception of orgasm, increasing the sensitivity of brain neurons related to the contraction of pelvic floor striated muscle, and promoting the orgasmic contraction of uterine and vaginal smooth muscle to support sexual orgasm.
Although some researchers consider that the purpose of female sexuality is not necessarily to attain orgasm and the absence of orgasm in sex activity can also be regarded as a complete sexual response cycle[29]. In fact, the related changes of female genitalia during orgasm create favorable conditions for fertilization. During and after climax, the pressure of uterine cavity undergoes a dramatic change from positive to negative pressure, which is conducive to absorbing sperm into the uterus [30, 31]. In addition, the cervix open slightly and uterine body lift upward at orgasm, with the external orifice of the cervix closer to the semen pool, facilitating the entrance of sperm to the uterine cavity. Moreover, studies [32] have reported that the blood flow of female reproductive organs elevates during excitement resulting in the increasement of cervical and vaginal secretions, with the vagina well-lubricated and the vaginal acidity buffered (the vaginal pH can rise to 7.2 and maintain for 6 ~ 8 hours after sexual intercourse[33-35]), which is also beneficial for sperm survival.
When the ovum is discharged out of the follicle, deterioration will occur in the ovulated mature oocyte if fertilization does not happen for a prolonged period in vivo or in vitro, which is called post-ovulatory aging（POA）. The correlation researches [36, 37] indicate that POA is closely linked to lower chance of conception, poor embryo quality and pregnancy loss. After sexual arousal, the peristalsis of fallopian tube enhances to pick up ovum released from the ovary, which creates favorable conditions for fertilization. Nevertheless, our results revealed that although the live birth rate was higher in the experimental group, there was no difference in the rates of biochemical pregnancy or miscarriage between the two groups. Consequently, we speculate that the clinical sample size should be expanded in the future so as to verify whether there is a correlation between sexual behavior and pregnancy outcomes.
In conclusion, on the basis of ovulation monitoring, the reproductive significance of maintaining the integrity of sexual response cycle is definitely apparent. Additionally, further detailed study is required to investigate the effect of sexual behavior on female endocrine and pregnancy outcomes. Notwithstanding, the clinical management of FSD is hampered to some extent by the sensitivity of sexual issues due to differences in region culture and religious beliefs. As a matter of fact, sex should not be considered as a taboo subject. Reproductive physicians should pay close attention to the sexual health of their patients so as to shorten the pre-pregnancy cycle of ovulation monitoring, improve the ovulation rate and clinical pregnancy rate, and reduce the occurrence of adverse pregnancy events.