Follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels are important in hormone testing. Here we discuss how they impact a woman's health.
Many hormones affect a woman's health.
Most important of these are estrogen, progesterone, testosterone, FSH (follicle stimulating hormone) and LH (luteinizing hormone).
Hormone fluctuations can be divided into three different phases: during the menstrual cycle, changes with age, and during pregnancy.
The graph above shows the cyclical rise and fall of these hormones during the periods.
At first, estrogen rises during the growth of follicles. Then a sharp surge of FSH and LH helps in ovulation. Finally, release of progesterone prepares the body for a possible pregnancy.
This cycle repeats almost every month from puberty until menopause. But during pregnancy, estrogen and progesterone levels continue to rise and FSH, LH levels drops to very low levels.
We have discussed the role of estrogen, progesterone, and testosterone in a separate article. Here we discuss the role of FSH and LH in a woman's health.
FSH and LH levels are important for a regular cycle and normal fertility. Imbalances in these hormones can cause irregular cycles and problems such as PCOS (polycystic ovarian syndrome) and disorders of pituitary and hypothalamic glands.
FSH is one of the eight key hormones of the pituitary glad. Others are LH, TSH, and GnRH. They all have two arms, one of which is always the same.
FSH is necessary for the production and growth of sperms in men and eggs in women. The part of ovaries and testes that make eggs & sperms have the cells that bind with FSH (called granulosa and Sertoli cells, respectively).
The rise in FSH levels is an indicator of drop in number of eggs (not quality of eggs); a test should be performed on day 2-5 of the cycle for most accurate results, especially during menopausal transition.
Estradiol prevents the release of FSH.
In a regular 28-day cycle, FSH levels are low when estradiol (E2) peaks (around days 13-14 & 24-25) and high when E2 dips (around days 15-16 & 1-8). See the graph above.
Similarly, during pregnancy, very high estrogen levels lead to very low FSH levels.
Inhibin B (a hormone responsible for number and quality of follicles) also behaves similarly.
Periods are generally accepted to last 28 days, similar to a lunar month.
However, data from carefully conducted studies do not support this idea. Not only periods are on average 29 days long, they vary a lot from woman-to-woman and change with age.
Irregular cycles are very common, some last for a few days and others even up to two months.
In general, cycles tend to get shorter with age: at puberty they are around 34 days and vary a lot until 25 years of age, then more regular cycles of about 28 days are common in the thirties. Irregular cycles become more frequent during perimenopause with average duration of 38 days.
However, no correlation has been found between the age of menarche (first period) and menopause.
For centuries, due to religious and cultural reasons, there has been a lot of focus on a woman's fertility window.
However, multiple studies suggest it's near impossible to time pregnancy by looking at the window of fertility. Similarly, efforts to predict sex at birth by using time of pregnancy have been futile.
As the chart above shows, peak time to get pregnant is around days 10 to 17, but only seen in about thirty percent of women.
But the fertility window can be very wide from day 6 until day 21. Above plot shows data from over seven hundred thoroughly studied births to confirm such a wide fertility window.
With age and more frequent irregular cycles, a woman's fertility window tends to shift to later days.
One in ten couples face some challenge in getting pregnant. And about half of them seek some kind of help.
Several factors can affect fertility. For example, lifestyle decisions around weight, smoking, sexually transmitted infections (STIs), and recreational drugs can cause problems with conceiving and pregnancy.
Chlamydia, gonorrhea and other sexually transmitted diseases are known to cause infertility. STIs are preventable and most are treatable after testing.
Out of a wide range of issues, the biggest factor in getting pregnant is a woman's age.
Because more women are delaying pregnancy and childbirth to focus on their careers, age is becoming an important factor in fertility discussion.
Over past 30 years, in vitro fertilization (IVF) has seen tremendous growth. In 2021, one in every twenty five children in US was born with assisted reproductive therapies such as IVF.
The chart below illustrates how the success rate of pregnancy with IVF drops rapidly once a woman enters her thirties.
Data from UK by Balen & Rutherford show that success of IVF (in-vitro fertilization) starts dropping once a woman reaches the age of thirty. The number and quality of follicles decline due to rise in FSH levels and a drop in ovarian reserve.
More research in IVF will certainly help improve the success rate. The biggest benefit should be from the better understanding of the embryo, and technologies to freeze, thaw, and implant.
That's because, out of 8-12 embryos collected during a cycle, success rate of an IVF procedure after freezing, thawing, and grafting is only 20-30%.
With age, the quality and number of embryos further drops due to rise in follicle stimulating hormone (FSH) and luteinizing hormone (LH).
An FSH test, performed on day 3 of menstrual cycle, is a good predictor of ovarian reserve to assess the quality and number of eggs.
Other options to predict a woman's ability to conceive include an ultrasound to check ovary size and number of eggs during that specific cycle, and testing for anti-Mullerian hormone (AMH) and Inhibin B levels.
For men, fertility starts to decline quickly after 55 years of age, and risk of genetic defects in babies becomes high.
Studies show that even at 35 years of age, a man has only half the success rate of conceiving a baby compared to when he was ten years younger.
Rise in infertility in men has been linked to chemicals from industrial pollution, since many of them are functionally similar to estrogen and estradiol hormones.
Studies comparing organic farmers with printers, electricians, metal workers and men working in industrial settings show a clear difference in sperm count.
Did you know that in ancient Greece, recommended age for marriage was 37 years for men and 18 years for women?
The goal was for both husband and wife to reach the end of their fertile years together (believed to be 50 for women and 70 for men) and then enjoy a healthy sexual life. (cf. Politics by Aristotle, Book 7:XVI)
FSH has a well-defined behavior in regular cycles. It is highest just before ovulation but otherwise levels are low throughout the menstrual cycle.
During pregnancy, FSH levels remain very low, especially after first trimester when the baby's placenta starts to release high levels of estrogen.
However, recent studies show FSH is necessary for a healthy pregnancy and delivery of the baby.
Estradiol is a good predictor of FSH because estrogens suppress FSH levels. After puberty, whenever estradiol levels rise in menstrual cycle, FSH drops.
With age, peak estradiol levels start dropping and FSH levels start rising, especially around menopause.
Because of such changes, as women enter their forties and fifties, they start to observe many changes in their bodies.
Age is clearly the biggest indicator of menopause and happens around the age of fifty-one. But the changes start several years before menopause.
Figure showing the rise in follicle stimulating hormone with age. Average age of menopause is about 51 years but FSH levels start rising at least six years before menopause.
There are several strong indicators of a transition to perimenopause and full menopause. Here we list a few of them:
A sharp rise in FSH levels about 6 years before menopause. FSH continues to increase until two year after menopause.
During periods—in the follicular phase—estrogen levels rise quickly and the first part of the cycle gets shorter. This sharper rise is also an indication of menopause.
Another hormone called AMH or Anti Mullerian Hormone (or Mullerian Inhibiting Substance) is released by the eggs. As the quality and number of eggs decline with age, AMH levels drop. In future, they might become the most reliable marker of menopause.
Inhibin A and Inhibin B are two other important chemicals released by the eggs. Inhibin A mostly indicates the health of the egg released during ovulation. Inhibin B reflects the total quantity and health of all the eggs. Since menopause impacts the quality and number of eggs, both Inhibin A and B can be used as early markers of menopause.
Inhibin A and Inhibin B are direct indicator of the quality and number of eggs. They are rarely measured due to high cost of the assays to reliably check them.
During menopause transition, estradiol drops and FSH rises. This is also the time when bone density starts dropping in women.
Estrogen is believed to be the main contributor in this change but some studies suggest FSH contributes more to bone loss & osteoporosis.
FSH may be responsible for an increase in fat around our waists as higher FSH levels are found in those with higher BMI and larger waist circumference. It may increase the risk of heart disease, atherosclerosis, and certain cancers.
In general, all key sex hormones including FSH, LH, estrogen, and progesterone decline with gain in weight.
FSH levels are low until puberty, but in rare cases might be observed during reproductive years.
One of the most common cases of abnormal FSH levels and LH levels is PCOS (polycystic ovary syndrome). Generally, low FSH and high LH to FSH ratio is found in people with PCOS.
Certain genetic disorders (e.g., Kallman syndrome) might prevent children from reaching puberty, keeping their FSH low.
The pituitary gland releases eight sex hormones, and any disorders of pituitary, known as hypopituitarism, can lead to low FSH levels.
In contrast, high prolactin hormone levels can suppress FSH production, leading to low FSH levels. This condition is called hyperprolactinemia.
Those taking hormone suppression medicines or have naturally low production by pituitary or the ovaries (or testes) might have unusually low FSH and LH levels.
High FSH levels are indication of infertility and but can be treated.
Unexpectedly high FSH levels in reproductive years indicate early menopause, failure or premature aging of the ovaries.
Certain genetic disorders can also cause high levels of follicle stimulating hormone. For example, missing or extra X chromosomes can lead to unusually high FSH levels.
Other genetic disorders that affect the pituitary gland, which controls FSH release, can also lead to unusually high levels.
Women are at higher risk of autoimmune diseases. Such disorders, e.g. lupus are believed to be related to certain sex hormones such as FSH, LH, estrogen, and progesterone.
Another important reproductive hormone for both men and women is luteinizing hormone (LH).
LH is released by the pituitary and shares one of the two arms with FSH, TSH (thyroid stimulating hormone), and hCG (human chorionic gonadotropin).
The pituitary releases LH in pulses at a regular interval, controlled by another key hormone called GnRH (gonadotropin-releasing hormone).
"Luteus" means yellow, which is the color of the egg and other mass released during ovulation.
Peak LH levels, called the "LH surge" which occurs a few hours before ovulation, is the hallmark of menstrual cycle. This suggests both FSH and LH levels have important roles in the release of dominant follicle as an egg.
The second half of menstrual cycle is called luteal phase, because of luteinizing hormone. This phase is more variable then the first part called follicular phase.
Irregular cycles, especially with age, are due to change in the pulse width and higher peaks the LH release by the pituitary gland.
Very low levels of LH are seen during pregnancy.
LH levels remain low until puberty, then remain steady during reproductive years before starting to increase in perimenopause. Very high LH levels are seen after menopause.
The sketch above shows rise in LH levels with age. A single test of FSH and LH may not be sufficient to check perimenopause. But regular testing can help confirm symptoms, such as hot flashes, insomnia, dry skin and other changes during a woman's menopause transition.
Order an at-home FSH / Ovarian Reserve test.
Order an at-home FSH / Ovarian Reserve test.
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Testosterone and Aging - how testosterone changes with age.
Hormones for Optimal Health – learn about some of the key hormones & their role.
Hormone Imbalance in Women - Role of Estrogen, Progesterone and Testosterone – learn about the three key hormones.
Saliva Testing - Advantages and Challenges – review of science on saliva based testing.
Sleep and the Role of Melatonin and Cortisol Levels – short summary of sleep problems and two key hormones.
Cortisol: Risk Factors – review of key risk factors for the stress hormones.
Morning Cortisol Levels – Why levels and collection times are so important.
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"Follicle-Stimulating Hormone: Fertility and Beyond," D Lizneva et. al., Front. Endocrinol., 2019.
"Serum follicle-stimulating hormone and luteinizing hormone levels in women aged 35-60 in the U.S. population: the Third National Health and Nutrition Examination Survey (NHANES III, 1988-1994)," LC Backer et. al., Menopause, 1999.
