Causes

The rates of EFS rise up every day, but this is, fortunately, still a very rare condition. Different scientific studies show different worldwide rates of the syndrome — from 0.045% to 3.4%. These variations in statistics can be explained.
In some studies patients who had no reaction (or extremely bad reaction) on the induction of ovulation or have some disorders of usual ovulation cycles were included to the rates while some other specialists considered better to except such patients from their statistics.

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Specialists cannot always find a real cause of such a condition. According to the clinical studies 1991-1996 some scientists even have a doubt that such a syndrome exists. But there is a list of potential causes:

Inappropriate timing of hCG (human chorionic gonadotropin).
HCG is a hormone produced by the syncytiotrophoblast, a portion of the placenta following implantation. The presence of hCG is detected in pregnancy tests.
The pituitary analog of hCG, known as luteinizing hormone (LH), is produced in the pituitary gland of males and females of all ages. HCG is heterodimeric, with an α (alpha) subunit identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and β (beta) subunit that is unique to hCG. The α (alpha) subunit is 92 amino acids long.
The β-subunit of hCG gonadotropin (beta-hCG) contains 145 amino acids, encoded by six highly homologous genes that are arranged in tandem and inverted pairs on chromosome 19q13.3 – CGB. Blood or urine tests measure hCG. Most tests employ a monoclonal antibody, which is specific to the β-subunit of hCG (β-hCG). This procedure is employed to ensure that tests do not make false positives by confusing hCG with LH and FSH. (The latter two are always present at varying levels in the body, whereas the presence of hCG almost always indicates pregnancy).
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Human chorionic gonadotropin is extensively used for final maturation induction in lieu of luteinizing hormone. In the presence of one or more mature ovarian follicles, ovulation can be triggered by the administration of HCG. As ovulation will happen between 38 and 40 hours after a single HCG injection, procedures can be scheduled to take advantage of this time sequence,such as intrauterine insemination or sexual intercourse.
Also, patients that undergo IVF, in general, receive HCG to trigger the ovulation process, but have an oocyte retrieval performed at about 34 to 36 hours after injection by, a few hours before the eggs actually would be released from the ovary.

• PCOS
Polycystic ovary syndrome is a hormonal non-cured disease, characterized by ovary dysfunction (non-ovulation or irregular ovulation, hyperproduction of estrogens and androgens). This disease causes a big hormonal disbalance which influence, in part, on estradiol level.
• Dysfunctional folliculogenesis, in which oocyte atresia occurs with normal hormonal response;
• Genetic factors;
• Age factor .

About 24% of patients with EFS are between the age of 35 to 39 years of age & 57% for those > 40 years of age. It has also 20% chances of recurrence & the risk of recurrence increases with advancing age of the patient.