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About Ovulation

 

Why test for Luteinising Hormone?

 

It is estimated that 10-15% of couples experience fertility problems during their reproductive life¹. There are only a limited number of days during a woman’s menstrual cycle when sexual intercourse might lead to pregnancy. The duration of the fertile period depends on the life span of both the sperm and the egg. Typically the egg is viable for up to 24 hours after ovulation². The life span of the sperm is much more variable and depends on a number of factors including the type and quality of cervical mucus present at the time of intercourse. In the presence of fertile mucus, sperm typically survives for 3-5 days³.

 

Women can, therefore, only conceive on around 5-6 days of their cycle and are most likely to conceive on the 2 days of peak fertility – the day of ovulation and the preceding day. Women who are trying to become pregnant should target their sexual intercourse around the time of ovulation to maximise their chances of conception³. The timing of ovulation can be determined through detection of luteinising hormone (LH) in urine, the hormone that triggers ovulation.

 

Luteinising Hormone

 

LH is a gonadotrophic hormone, produced by the anterior pituitary gland. Secretion of LH is pulsatile, occurring every 70 to 100 minutes⁴. Basal levels of LH in the urine are typically 6-13 mIU/ml^2,4. A significant surge in LH level is seen approximately 24-36 hours before ovulation, typically lasting 1-2 days and rising to at least 3 times the basal level (~50-200 mIU/ml). This therefore makes LH an excellent marker for ovulation⁵.

 

The LH molecule is dimeric, having an a and b subunit. The a subunit is common to all the four glycoprotein hormones, luteinising hormone (LH), human chorionic gonadotrophin (hCG) follicle stimulating hormone (FSH) and thyroid stimulating hormone (TSH). The b subunit is unique to each hormone and responsible for its biological activity⁶.

 

The Menstrual Cycle

 

A woman’s menstrual cycle begins on the day her period starts (first day of full menstrual flow), and ends the day before her next period starts. At the beginning of the cycle during the follicular phase, FSH stimulates the ovaries to grow egg follicles, and to secrete oestrogen. Whilst a number of follicles will be stimulated to grow, normally only one will be selected to go through the complete maturation process and be released at ovulation⁷.

 

When oestrogen reaches a critical level, it induces a surge in LH. This is the hormone that triggers events that lead to ovulation. Ovulation is when the ovarian follicle ruptures and the egg is released. Ovulation signifies the beginning of the luteal phase of the menstrual cycle. During the luteal phase, the empty ovarian follicle forms the corpus luteum which begins to produce progesterone. Progesterone and oestrogen prepare the womb for nurturing pregnancy by stimulating the thickening of the endometrium (lining of the womb) in readiness for implantation of a fertilised egg. If the egg is unfertilised, or implantation does not occur, progesterone and oestrogen levels fall, causing the endometrium to shed (menstruation) and a new menstrual cycle begins^7,8.

 

Measurement of hormones or analysis of endocrine function can therefore be employed to help identify when ovulation occurs.

 

Other Methods of Ovulation Detection

 

Rhythm Calendar Method

 

The Rhythm Method of ovulation detection requires the woman to estimate her expected ovulation day through knowledge of her own cycle length⁹. It is known that the luteal phase of the menstrual cycle is fairly constant amongst women at 14 days (typical range 12-16 days)¹⁰. This information coupled with the woman’s own knowledge of her cycle lengths can be used to identify the fertile phase in her cycle. This method, however, is only of practical use to women with consistently regular cycles.

 

Basal Body Temperature Method

 

The Basal Body Temperature Method requires the woman to use a sensitive thermometer to measure her body temperature every morning before she gets up. Following ovulation, the empty follicle or corpus luteum produces progesterone. The secretion of progesterone is accompanied by a temperature rise of 0.2^oC –0.4^oC and so can indicate that ovulation has taken place¹¹. However, the most fertile phase in a woman’s cycle is on the day of ovulation and the day preceding ovulation² and so ovulation will have been missed by the time a shift in body temperature is detected. The Basal Body Temperature Method is therefore only useful in retrospect for future cycles assuming the woman’s cycles are regular. However, basal body temperature can change in response to alcohol, illness and lack of sleep and so it can be difficult to determine the precise day of progesterone production.

 

BillingsMethod

 

Billings Method identifies changes in cervical mucus that occur in the fertile phase of the cycle. To perform this method, a woman has to examine a sample of her cervical mucus every day. As ovulation approaches, mucus will become thinner and less sticky to help the passage of sperm to reach a released egg. Once this change in the consistency of the mucus is observed, ovulation should occur very shortly afterwards¹². Infections and the presence of semen can affect the consistency of the mucus and so it can be difficult to determine the fertile phase using this method and the method also requires some training and practice.

 

Ultrasonography

 

Ultrasonography can be used to monitor the development of the dominant follicle and, if timed correctly, to witness the event of ovulation itself^13,14. However, this is an expensive and time-consuming method.

 

Serum Progesterone Levels

 

Ovulation can be confirmed by measuring progesterone levels in the woman’s blood approximately 7 days after ovulation or 7 days before the expected start of the next cycle, typically on day 21 of a 28-day cycle (which assumes that ovulation has occurred on day 14)¹⁵. This test can only confirm retrospectively that ovulation has occurred. It does not help the woman to target intercourse on her fertile days for that cycle.

 

Salivary Ferning

 

Changes in oestrogen levels in circulation can affect physical properties of saliva. However, the results often give too large a number of possibly fertile days to be of practical use and do not correlate well with detection of ovulation by ultrasound. Also the method is very hard to use accurately¹⁶.

 

Rapid Immunoassay - Clearview EASY LH

 

Clearview EASY LH is a monoclonal antibody-based immunoassay for the qualitative detection of luteinising hormone (LH) in urine as an aid to finding the LH surge and can therefore predict the timing of ovulation.

 

 

References

 

1. Evers J.L. (2002). Female Subfertility. Lancet 360(9327): 151-159
   
2. Testart J. & Frydman R. (1982). Minimum time lapse between luteinising hormone surge of hCG administration and follicular rupture. Fertil Steril 37: 50-53
   
3. Wilcox A.J., Weinburg C.R. & Baird D.D. (1995). Timing of Sexual Intercourse in Relation to Ovulation. N Engl J Med 333(23): 1517-1521
   
4. Nulsen J., Wheeler C., Ausmans M. & Blasco L.; Cervical Mucus Changes in Relationship to Urinary Luteinizing Hormone (1987) Fertil. Steril. 48: 783
   
5. Corsan G.H., Ghazi D. & Kemmann E. (1990) Home Urinary Luteinizing Hormone Immunoassays: Clinical Applications. Fertil. Steril. 53: 591-601.
   
6. Ulloa-Aguirre A., Maldonado A., Damian-Matsummura P. & Timossi C. (2001) Endocrine Regulation of Gonadotropin Glycosylation: Archives of Medical Research: 32: 520-532.
   
7. Griffen J.E. & Ojeda S.R. (1988) Textbook of Endocrinology. Oxford University Press.
   
8. Behre H. M., Kuhlage J., Gaßner C., Sonntag B., Schem C., Schneider H. P. G. & Nieschlag E. (2000) Prediction of ovulation by urinary hormone measurements with the home use Clearplan® Fertility Monitor: comparison with transvaginal ultrasound scans and serum hormone measurements. Human Reproduction. 15(12), 2478-2482.
   
9. Royston P. (1991) Identifying the fertile phase of the human menstrual cycle. Stat. Med. 10(2), 221-240.
   
10. Hussa R.O. (1987) The clinical marker hCG. Praeger.
    
11. Lenton E.A., Weston G.A. & Cooke I.D. (1977) Problems in Using Basal Body Temperature Recordings in an Infertility Clinic. BMJ. 1: 803-805.
    
12. Hume K. (1991) Fertility Awareness in the 1990's - the Billings Ovulation Method of Family Planning, its Scientific Basis, Practical Application & Effectiveness. Advances in Contraception. 7: 301-311.
    
13. Depares J., Ryder R.E., Walker S.M., Scanlon M.F. (1986) Ovarian ultrasonography highlights precision of symptoms of ovulation as markers of ovulation. BMJ. 292: 1562.
    
14. Leader A., Wiseman D. & Taylor P.J.(1985) The Prediction of Ovulation: A Comparison of the Basal Body Temperature Graph, Cervical Mucus Score and Real-Time Pelvic Ultrasonography. Fertil. Steril. 43: 385-388.
    
15. Serafini P., Stone B., Kerin J., Batzofin J., Quinn P. & Marrs R.P. (1988) Occurrence of a Spontaneous Luteinizing Hormone Surge in Superovulated Cycles - Predictive Value of Serum Progesterone. Fertil. Steril. 49: 86-89.
    
16. Guida M., Tommaselli G. A., Palomba S., Pellicano M., Moccia G., Carlo C. & Nappi C. (1999) Efficacy of methods for determining ovulation in a natural family planning program. Fertility and Sterility. 72(5), 900-904.