Fertility is the ability to conceive a child. Most of us take our fertility for granted but the process of reproduction is complex, so some people may experience difficulties when trying for a baby. There are a range of factors that can affect fertility.
Taking care of your preconception health by modifying your lifestyle can improve your chance of a pregnancy and the health of your future child. Medical conditions such as polycystic ovary syndrome PCOS and endometriosis can reduce fertility, however it may just take longer to get pregnant.
In some cases, medical procedures can be used to preserve fertility. Fertility preservation freezing of gametes for later use is used by people who are not ready to have a baby during their most fertile years or for those facing medical treatment that might impair their fertility.
Understanding reproduction It is useful to understand how eggs and sperm are normally formed, and how conception occurs to understand the causes of infertility and how they are targeted in fertility treatment. The hormones which control the production of sperm and eggs are called gonadotrophins. In men, they stimulate the testicles to produce sperm and testosterone. In women, they act on the ovaries where the eggs develop. The female sex hormones, oestrogen and progesterone, are produced by the ovaries when eggs mature and are released ovulation.
For women, the production of sex hormones and the release of an egg is known as the menstrual cycle. It is counted from the first day of the period until the day before the start of the next period.
In an average cycle of 28 days, ovulation happens on day However, cycle length varies between women, and it is important to note that ovulation occurs earlier in women with shorter cycles and later in women with longer cycles.
Sperm are produced at the rate of about million per day. They take some 80 days to mature. Each sperm has a head, which contains the genetic material, and a tail, which propels it up through the vagina, uterus, and fallopian tubes where the egg is fertilised. Conception occurs when an egg and a sperm come together. At ovulation, an egg is released from the ovary into the fallopian tube. If sperm is present at that time, the egg can be fertilised.
The fertilised egg then starts to divide and becomes an embryo. After ovulation, the ovary produces progesterone which prepares the lining of the uterus - the endometrium - for the growing embryo. A few days after implantation, the embryo starts to produce human chorionic gonadotrophins HCG - the hormone that gives a positive pregnancy test reading.
In a classical negative feedback loop , sex steroids inhibit secretion of GnRH and also appear to have direct negative effects on gonadotrophs. In females, pulse frequency is clearly related to stage of the cycle. Numerous hormones influence GnRH secretion, and positive and negative control over GnRH and gonadotropin secretion is actually considerably more complex than depicted in the figure.
For example, the gonads secrete at least two additional hormones - inhibin and activin - which selectively inhibit and activate FSH secretion from the pituitary.
This condition is typically manifest in males as failure in production of normal numbers of sperm. In females, cessation of reproductive cycles is commonly observed. Elevated blood levels of gonadotropins usually reflect lack of steroid negative feedback. Removal of the gonads from either males or females, as is commonly done to animals, leads to persistent elevation in LH and FSH.
In general, elevated levels of gonadotropins per se have no biological effect. Normal patterns of gonadotropin secretion are absolutely required for reproduction, and interfering particularly with LH secretion is a widely-used strategy for contraception.
Oral contraceptive pills contain a progestin progesterone-mimicking compound , usually combined with an estrogen. As discussed above, progesterone and estrogen inhibit LH secretion, and oral contraceptives are effective because they inhibit the LH surge that induces ovulation. Another route to suppressing gonadotropin secretion is to block the GnRH receptor. The growth of the seminiferous tubules and maintenance of spermatogenesis in men are regulated by FSH.
However, androgens, unlike estrogens, do not lower FSH levels, therefore demonstrating a feedback relationship only with serum LH. For reasons not fully understood, azospermic and oligospermic males usually have elevated FSH levels. Tumors of the testes generally depress serum FSH concentrations, but levels of LH are elevated, as determined by radioimmunoassay. It has been postulated that the apparent LH increase may be caused by crossreactivity with hCG-like substances secreted by tumors of the testes.
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