How likely is it that fertilization will occur during ovulation and sex?
The average probability of fertilization depends on the time of sexual intercourse during the fertile period. The probability increases with the proximity of ovulation. The fertile time window is usually five days before and one day after ovulation. The average probability of fertilisation is about ten percent if sexual intercourse takes place five days before ovulation. The highest probability of about 25 – 30 percent can be reached one day before as well as on the day of ovulation.
When is the optimal time for sex so that ovulation leads to fertilization?
In order to determine the optimal time for sexual intercourse leading to fertilisation, it is first of all essential to know your own monthly cycle. Since the length of the menstrual cycle can vary from woman to woman, it is also impossible to make a generally valid statement about when ovulation takes place and therefore sexual intercourse is most likely to lead to fertilisation. It is therefore advisable to first observe the monthly cycle closely, for example by using
- The temperature method,
- With the aid of commercially available urine tests that can determine ovulation, or
- With the help of numerous online calculators or even tables that can be used as a guide during a regular cycle and predict the possible time window for fertilisation.
Development and maturation of the gametes
Already as an embryo, millions of female gametes (oogonia) are created in the female reproductive systems (gonads). By puberty, a large proportion of the oogonia are lost, leaving only 40,000 of them until the egg is ready for fertilisation. All oogonia still contain the double (diploid) set of chromosomes (46XX) and must be transformed into haploid germ cells (23X) by two maturation divisions (meiosis), so that the union of egg and sperm (fertilization of the egg) again results in a diploid egg (46X?).
For ovulation to occur, an interaction of female hormones in the organism must be ensured. First, the concentration of follicle-stimulating hormone (FSH) secreted by the pituitary gland increases. The follicles form FSH receptors in their inner granulose layer.
The more FSH receptors a follicle has, the more oestrogen is produced by the follicle. The follicle with the highest oestrogen production becomes dominant under the influence of FSH together with the luteinizing hormone (LH) and leads to the decline of the other follicles. The estrogen produced by the dominant follicle inhibits the release of FSH, causing other follicles to decline and ultimately LH to take over.
LH promotes the conversion of hormone synthesis in the granulosa cells to the production of corpus luteum hormone (progesterone). Ovulation takes place about 44 hours after the start of the LH surge. The corpus luteum develops from the rest of the remaining follicle.
The granulosa cells develop into the luteal cells of the corpus luteum, which produce progesterone to maintain a possible pregnancy. The secretion maximum is reached on the 7th day after ovulation, the time of a possible implantation of the egg. If the egg is implanted, the corpus luteum becomes the corpus luteum graviditatis.
Otherwise, the corpus luteum perishes. It must be remembered that the woman’s cracked egg must be fertilised within 12 hours for implantation to take place. The male gametes are also subject to meiosis, so that diploid gametes become haploid (half a set of chromosomes).
In contrast to women, however, spermtaogenesis does not take place until the beginning of puberty and lasts a lifetime. In the testicles of sexually mature men, about 1 million sperm are produced daily under the influence of adrogens. The spermatogonia develops into the primary spermatocyte with two chromatid chromosomes and a diploid set of chromosomes.
After the first maturation division, two haploid secondary spermatocytes emerge from the primary spermatozyte. After the second maturation division, two secondary spermatocytes finally give rise to four haploid spermatids with a haploid chromosome set and one-chromatid chromosomes. Two spermatids each contain the X chromosome, while the other two contain the Y chromosome.
The spermatids then mature into sperm (spermatozoon) in the epididymal duct (Ductus epididimydis). During sexual intercourse (cohabitation), the spermatozoon reach the prostate gland through the epididymal duct and, together with the glandular secretions from the prostate and the vesicle gland, form the ejaculate for possible fertilisation of the egg cell. This ejaculate is expelled from the urethra towards the vaginal vault. The ejaculate is an alkaline liquid rich in fructose and represents the optimal environment for motility and survival of the spermatozoon. The spermatozoon consists of the sperm head with the genetic material it contains, the mobile middle part and the sperm tail.
