Causes for Infertility

 

The causes of infertility could be originated from both women and men. Actually, female factor and male factor each contributed to 40% of the infertility couples. 10% of the couples are caused by unknown factors and 10% are caused by both parties.

2.1 Infertility in Men

2.1.1 Disorder in sperm production

The major male problem causing infertility is the disorder in sperm production and it accounts for 75% of the male infertility problems. Besides the reduced sperm count, it also includes poor sperm motility and abnormal morphology. 

The defects may be due to genetic causes, smoking, alcohol, chemical pollution exposure, genital tract surgery, vein congestion in scrotum and infection. Often the cause cannot be found.

 

2.1.2 Anatomical or structural problems

The sperm is manufactured in the testis and is then stored in the coiled tubules surrounding the testis. During intercourse, the sperm will be propelled by the vas deferens into the urethra and ejaculated in the form of semen. That is why blockages along any point of the pathway may cause infertility.

 

2.2 Infertility in Women

2.2.1 Advanced Age

 

Relationship between age and egg reserve

As quoted from the Census and Statistics Department, the median age at first delivery was postponed by 4.7 years to 29.8 years-old from 1981 to 2008. This may be one of the reasons contributing to the increasing infertility rate in Hong Kong.

The number of eggs in women is limited and starts to decline from birth, as the ovary does not produce any new eggs after the embryo stage and it continues to diminish from childhood due to egg degeneration. When puberty is reached, egg loss continues due to ovulation with other non-ovulating eggs undergoing atresia. Apart from the reduced quantity of eggs, egg quality also deteriorates as age increases. The live birth rate actually declines by approximately 1% each year as the woman ages.

 

Relationship between age and miscarriage

There is a higher incidence of endometriosis and uterine fibroids as women get older. These defects may distort the uterine lining and cause a higher risk of miscarriage. The miscarriage rate is 33% in older women while it is only 10% in younger women.

 

Relationship between age and success rate of ART

Age is also an important factor for the success in ART treatment. ART success rate can reach 50%-60% for women under 30, 30%-40% at the age of 30-40 and the rate decreases rapidly to 20% and below after the age of 40. Due to the correlation of age and fertility, couples are generally advised to seek medical advices as early as possible. 

 

2.2.2 Ovulation Disorders

Ovulation disorders accounted for 40% of the female infertility. There are various causes for this; the most common cause is Polycystic Ovarian Syndrome (PCOS).

 

Polycystic Ovarian Syndrome (PCOS)

Multiple tiny cysts exist in the ovaries of PCOS patients. These cysts are not harmful to the body, however, it can cause irregular or no ovulation and so increases the chance of infertility. The affected women may show raised blood hormone LH:FSH ratio and testosterone level, increased body weight and/or body hair, acne and abnormal insulin level.

 

Premature Ovarian Failure

Under normal circumstances, the ovaries run out of eggs and stop functioning at menopausal age. Yet, various unknown reasons may cause ovarian failure in younger women. Some studies suggest that this condition may be due to the exposure to chemical or medical treatments, various autoimmune diseases and genetic disorders.

 

Hypothalamic Amenorrhea

Amenorrhea refers to the condition of no mense. This occurs when there is no gonadotropin-releasing hormone (GnRH) production in the hypothalamus. Women undergone constant stresses, abrupt change in weight, excessive exercise and lack in nutrients, have an increased chance of amenorrhea. Genetic abnormalities may contribute to some of the cases; however, the chances are very rare.

2.2.3 Structural Problems in Female Reproductive System

Endometriosis

Endometriosis occurs in 5%-10% of the general women at reproductive age. It refers to the medical condition in which the endometrial like tissue grows in areas other than the uterine cavity. Symptoms often worsen with time of the menstrual cycle due to the increase of various female hormones. The abnormal endometrial tissue may affect ovulation or obstruct the Fallopian tubes and the fertilization process.

 

Uterine Fibroids

A uterine fibroid is a benign tumor which originates from the smooth uterine muscle layer and the connective tissue. It often occurs in women of middle and later reproductive years. Some of the affected women may have no symptoms while others may suffer heavy menstruation flow, urinary frequency, urgency, painful menstruation and sexual intercourse. The fibroids could be very small or occur in location that they will not affect any reproductive functions. However, if the fibroid is large and if it is located inside the uterine cavity, it may have large impact on reproductive functions. Fibroids can often be cured by surgery to improve fertility.

2.2.4 Others

Tubal Diseases

Tubal disease is one of the common factors causing infertility. The Fallopian tube is the pathway travelled by sperms to reach the egg after it has been released from the ovary and it is where fertilization occurs. The fertilized embryo then travels along the tube to reach the uterus where implantation occurs. The women affected by tubal disease may have both or just one tube blocked. Other times, there can be simply tubal scarring or other tubal damage without tubal blockage.Tubal disease is often caused by either pelvic infection or pelvic endometriosis. It may also be the scar tissue formed after pelvic surgery. IVF is a promising method in treating infertility caused by tubal factor.

Hyperprolactinemia

Hyperprolactinemia happens when the pituitary gland produces excessive amounts of the hormone, prolactin. Prolactin is a hormone generally produced after delivery for the suppression of ovulation. The abnormal production of prolactin suppresses GnRH release hence ovulation. Hyperprolactinemia can be due to no identifiable cause or microprolactinoma in the pituitary; treatment is possible by using medication such as  e.g. Bromocriptine, Quinagolide and Cabergoline.

不育的成因

不育的成因可能來自女方和男方。事實上,在所有不育個案中,女方因素和男方因素各佔40%,10%為男女雙方均有影響,其餘10% 原因不明。

2.1 男性不育

2.1.1 精子製造異常

男性不育的主要原因是精子製造異常,佔75%。精子製造異常除了包括精子數目稀少,還包括精子活動力欠佳和形態不正常。 

這些毛病可能是由遺傳、吸煙、酗酒、化學污染、結紮手術、陰囊靜脈充血或發炎所致,有時甚至原因不明。

 

2.1.2 結構性問題

精子在睪丸內製成,儲存於附近的捲曲細管裡。性交期間,輸精管會將精子推送至尿道,再以精液狀態射出。因此,若沿途任何一處堵塞,都會引致不育。

 

2.2 女性不育

2.2.1 高齡

年齡和卵子數量之關係

根據香港政府統計處數據,2008年,港人第一次分娩的年齡中位數為29.8歲,比1981年延遲了4.7歲。這可能是香港不育率上升的其中一個原因。

女性的卵子數量有限,從出生一刻便開始減少。胚胎階段過後,卵巢便不會再製造新的卵子。從童年開始,卵子便不斷退化減少。踏入青春期,未受精的卵子會萎縮並排出體外,因此卵子數目會繼續下降。隨著年紀增長,除了卵子數量下降,卵子品質亦會下降。女性每年長一歲,活產率就會下降約1%。

 

年齡和流產之關係

女性年紀愈大,患上子宮內膜異位症和子宮肌瘤的機會就愈高。這些毛病可能會令子宮內膜變形,增加流產的風險。年長女性的流產率為33%,年輕女性則只有10%。

 

年齡和輔助生育技術(ART)成功率之關係

年齡是輔助生育技術(ART)治療成功與否的一大關鍵。對於30歲以下女性,ART的成功率可達50-60%,30-40歲為30-40%,40歲以上則急降至低於20%。基於年齡和受孕率關係密切,我們建議夫婦儘早尋求醫學意見。

 

2.2.2 排卵異常

40%的女方不育個案是源於排卵異常。排卵異常的原因各異,最常見的是多嚢卵巢症候群 (PCOS)。

 

多嚢卵巢症候群 (PCOS)

多嚢卵巢症候群(PCOS)病人的卵巢佈滿著微小的囊腫。雖然這些囊腫對身體無害,卻會引致排卵不定期,甚至無排卵,增加不育的機會。患者可能會出現黃體生成激素和促卵泡素的比例(LH:FSH)過高、雄性激素過多、體重、體毛和暗瘡增加、胰島素水平不正常等問題。

 

卵巢提早衰竭

一般情況下,在更年期時,當卵巢裡的卵子用盡,卵巢便會停止運作。不過,各種不明原因也會導致年輕女性卵巢衰竭。一些研究指出,此情況可能是由接觸化學品、醫學治療和各種自身免疫病及遺傳病所引起。

 

下視丘性無月經症

無月經症是指當下視丘無法製造促性腺釋放激素(GnRH)時,月經不來潮的現象。長期受壓、體重突變、運動過量和缺乏營養都會增加患上無月經症的機會。有很少數個案可能是源自基因異常,但可能性極低。

 

2.2.3 女方生殖系統的結構性問題

 

子宮內膜異位症

一般處於生育年齡的女性,5-10%會患上子宮內膜異位症,即是子宮內膜組織在子宮腔以外的地方增生。來經期間,各種女性荷爾蒙增加,症狀有時會加劇。不正常的子宮內膜組織可能會影響排卵,甚至堵塞輸卵管,阻礙受精過程。

 

子宮肌瘤

子宮肌瘤是一種良性瘤,生長於平滑的子宮肌層和結合組織上,一般在女性生育年齡的中後期發生。患者可能會出現月經流量極多、尿頻尿急、經痛和性交疼痛等症狀,有些則沒有任何症狀。

肌瘤的體積可能很小,或長在一些毫不影響生殖功能的地方。不過,若肌瘤體積大,並且長在子宮腔內,對生殖功能的影響則可以很大。肌瘤一般可靠手術治好,增加受孕率。

2.2.4 其他

輸卵管疾病

輸卵管疾病是常見的不育原因之一。卵子從卵巢釋放出來,精子游到輸卵管裡與卵子結合,也就是說輸卵管是卵子受精的地方。然後,受精的胚胎沿著輸卵管被動地移至子宮腔內,進行著床。患者可能是其中一條或兩條輸卵管皆閉塞,其他情況則只是輸卵管有瘢痕或受損,而不是閉塞。

輸卵管疾病的成因通常是盆腔發炎和子宮內膜異位症,或是盆腔手術後形成的瘢痕組織所致。要治療輸卵管因素引起的不育問題,體外受精(IVF)是個很有效的方法。

催乳激素過高症

催乳激素是一種女性分娩後為了抑壓排卵而產生出來的荷爾蒙。當腦下垂體分泌的催乳激素過量,就會出現催乳激素過高症。不正常的催乳激素分泌,會抑壓促性腺釋放激素(GnRH)的釋出,繼而影響排卵。催乳激素過高症的原因可能是腦下垂體長了微激乳素腺瘤,也可能原因不明。此症可透過藥物治療,例如:Bromocriptine、Quinagolide和Cabergoline。

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