Endocrine markers of ovarian function: Clinical and biological aspects with focus on Anti Müllerian hormone
Abstract: Popular Abstract in English During recent decades, significant changes in fertility pattern are seen in the Western World. Declining birth rates and smaller family sizes affect the population size, but also cause unwanted effects for the desired number of children to be achieved by the individual couple. Also involuntary childlessness is a consequence of postponing childbearing to an age where the chance of spontaneous pregnancy is less likely. A major age-related factor to limit a couple’s chance of conception is the declining quantity and quality of the eggs in the women’s ovary. The total amount of eggs available for a woman during her reproductive life is deposited in the ovaries as a number of quiescent eggs already in fetal life. On the earliest stages of development the pool of eggs reaches millions in number, but a vast majority of them decay before the female has reached her reproductive age. During women’s fertile period of life, a proportion of these non-growing eggs are activated to grow throughout 5-6 months and finally reach a stage where they can ovulate and become fertilized or go through so-called programmed cell death. In this manner, women’s supply of eggs is slowly depleted and finally, when all eggs are used, menopause will occur. The term ovarian reserve designates the pool of eggs present in the ovaries at any given time. A huge individual difference is seen in the size of the initial pool and how rapidly it is used. For a woman or a couple planning to build a family, questions like; when to start to reproduce and how long could pregnancy potentially be postponed without jeopardizing the chance of obtaining a family of a size of choice often are raised. In order to be able to answer these questions professionally, a reliable test to assess ovarian reserve, including the amount of remaining eggs in the ovaries, is requested. Today, the levels of Anti Müllerian Hormone (AMH) or the number of small follicles measurable by ultrasound are considered to be the best markers of ovarian reserve. Both tests measure certain developing stages in between the quiescent stage and eggs ready to be selected for ovulation, and this number mirrors the number of remaining eggs in the ovaries. Several scientific publications claim AMH to be so stable a test that only one blood test is sufficient for estimating a woman’s ovarian reserve. Also different cut-off levels believed to predict the chance of natural as well as assisted conception are suggested. For a quiescent egg in the ovary to be activated and start growing, a signal from the brain is necessary. The signal originates in the part of the brain called the hypothalamus and is transmitted to the hypophysis via a signal substance named Gonadotropin Releasing Factor (GnRh). This signal controls two hormones secreted from the hypophysis, the Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH), which both are brought to the ovaries by the blood and exert a crucial impact on the recruitment of quiescent follicles to start growing into an ovulating follicle. In order to add more clinically useful knowledge, the aim of the present thesis was to explore whether there is a variation over time in secretion of AMH, and to study its relation to the two gonadotropins; FSH and LH. In studies I and II, the variability of AMH was examined throughout 24 hours (circadian variation), by drawing blood for analysis every second hour from 8:00 a.m. the first morning, until the next. The study was performed both in normal menstruating women as well as in women diagnosed with Polycystic Ovary Syndrome (PCOS), which is a fairly common endocrine disorder in young women, characterized by anovulation, causing infertility and ovaries with numerous of small follicles. This group of women was chosen for the study since AMH is produced in the small follicles. Hence, the levels of AMH in PCOS women are much higher compared to normally menstruating women. The stability of AMH was also tested over three menstrual cycles by blood tests every fifth day. To find out whether the level of AMH was correlated to the number of small follicles, a three-dimensional vaginal ultrasound was performed at the fifth day of the menstrual cycle. In Study III, the variation of AMH and its co-variation to the antral follicle count was explored over 3 menstrual cycles. In study IV, blood from pregnant women was analyzed and the level of AMH related to the number of months necessary to obtain pregnancy. The aim of the study was to test AMH as marker of fertility in women/couples with normal fertility. The data for this study came from women in Ukraine, Poland and Greenland. 16 In study V, we wanted to explore if the level of LH in women undergoing In Vitro Fertilization (IVF) could influence the result of the treatment. This was performed by measuring the level of LH in 207 women undergoing hormonal stimulation prior to IVF. According to the level of LH, the women were divided into groups and compared by the number of eggs retrieved, fertilization and pregnancy rate. The results of this thesis reveal that normal menstruating women show a significant circadian variation in AMH. Also, for this group of women, AMH levels were shown to fluctuate significantly, both between cycle days within one cycle as well as between cycles. Furthermore, data from the thesis show that in women with PCOS, the level of AMH in average was three-fold higher compared to the normal menstruating women. However, the circadian variation in AMH as seen for the normal menstruating women was not seen for those with PCOS. For both groups, however, a clear correlation between levels of AMH and LH was found, suggesting that LH masters the secretion of AMH. Moreover, a significant positive correlation was found between levels of AMH and the number of small antral follicles. This finding was, however, expected as AMH is produced in such small follicles. Moreover, in a cohort of women obtaining spontaneous pregnancy, levels of AMH were found to be related to the number of months required to obtain pregnancy. In women undergoing hormonal stimulation prior to IVF, the rate of pregnancy and the consumption of hormones required for the hormonal stimulation were correlated to the LH levels. The number of successful pregnancies, as well as the amount of stimulating hormones needed, decreased by rising levels of LH. In conclusion, results from the present thesis have demonstrated that AMH is closely linked to LH, both key factors during development and recruitment of follicles and eggs. In women with a normal menstrual cycle, the level of AMH fluctuates significantly, both between cycle days within one cycle as well as between menstrual cycles. These fluctuations reach such an extent, that the current practice of using only one measurement of AMH to evaluate the ovarian reserve in a woman is questioned. Despite this, AMH seems to have the potential to indirectly measure a couple’s chance of obtaining pregnancy, as the time to pregnancy is longest in couples where AMH levels are lowest.
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