What Are FSH, LH, Estrogen, and Progesterone?

FSH, LH, estrogen (estradiol, E2), and progesterone are the four key hormones that regulate the menstrual cycle and fertility.

FSH (Follicle-Stimulating Hormone) is released by the pituitary gland and stimulates ovarian follicles to grow. Each follicle contains an egg, and FSH helps the dominant follicle mature.

Estrogen (Estradiol, E2) is produced by the developing follicle. It thickens the uterine lining and signals that the egg is approaching maturity.

A high estrogen level triggers the LH (Luteinizing Hormone) surge, which causes ovulation, usually within 24–36 hours, releasing the mature egg.

After ovulation, the empty follicle becomes the corpus luteum, which produces progesterone. Progesterone prepares and maintains the uterine lining for implantation. If pregnancy does not occur, progesterone levels fall, and menstruation begins.

Hormone testing helps evaluate ovulation, ovarian reserve, irregular cycles, PCOS, and fertility. FSH, LH, and estradiol are typically measured on days 2–4 of the menstrual cycle, while progesterone is best measured about 7 days after ovulation.

Understanding these hormones is an important step in assessing reproductive health and identifying potential fertility concerns.

The endometrium is the inner lining of the uterus where an embryo implants. Its thickness changes throughout the menstrual cycle in response to estrogen and progesterone.

A thinner uterine lining may sometimes be associated with lower implantation potential, particularly during IVF or frozen embryo transfer. However, thickness is only one part of the fertility picture. Blood flow, hormone levels, uterine health, embryo quality, age, cycle timing, and medical history may also affect the chance of pregnancy.

Possible factors linked with a persistently thin lining include hormonal concerns, reduced uterine blood flow, previous uterine procedures, inflammation, or scar tissue.

If an ultrasound shows a thin lining, the result should be reviewed together with the timing of the scan and your overall fertility history. One measurement alone does not provide the full picture.

When it comes to fertility, there’s no shortage of advice—but not all of it is accurate. Here are a few common myths we often hear:

Myth #1: If you have regular periods, you’re definitely ovulating.
Not always. While regular cycles often suggest ovulation, they don’t guarantee that an egg is being released every month.

Myth #2: Fertility is only a woman’s concern.
Male factors contribute to nearly half of all infertility cases. Evaluating both partners is an important part of a fertility assessment.

Myth #3: Low AMH means you can’t get pregnant.
AMH measures ovarian reserve, not egg quality. Many women with low AMH have gone on to achieve successful pregnancies.

Myth #4: Age only affects female fertility.
Male fertility also changes with age. Sperm quality and DNA integrity can gradually decline over time.

Myth #5: If pregnancy hasn’t happened after a few months, something must be wrong.
For healthy couples under 35, it can take up to a year to conceive naturally. If you’re over 35, or have known reproductive concerns, it’s a good idea to seek an earlier evaluation.

Understanding the facts can help you make informed decisions and avoid unnecessary stress. Every fertility journey is unique, and a personalized assessment is often the best place to start.

Many women worry after hearing they have a low AMH or low ovarian reserve, but it’s important to understand that egg quantity and egg quality are not the same thing. Egg quantity refers to how many eggs remain in your ovaries. Tests such as AMH and antral follicle count (AFC) estimate your ovarian reserve. A lower egg count doesn’t necessarily mean you can’t get pregnant—it simply means there are fewer eggs available. Egg quality refers to how healthy those eggs are. Healthy eggs are more likely to fertilize, develop into healthy embryos, implant successfully, and lead to a healthy pregnancy. While egg quality naturally declines with age—especially after 35—it isn’t measured by AMH alone. One of the most common misconceptions is that low AMH equals poor egg quality. Fortunately, that’s not always true. Many women with low AMH still conceive naturally or have successful IVF outcomes. Supporting your fertility involves more than looking at one lab result. A healthy lifestyle, good nutrition, quality sleep, stress management, and appropriate medical care all play important roles. Traditional Chinese Medicine may also help support reproductive health by promoting healthy menstrual cycles and improving overall wellness. Every fertility journey is unique. Rather than focusing on a single number, it’s important to evaluate the whole picture—including your age, hormone levels, menstrual history, and overall health.

The short answer is yes.

Before Pregnancy
Ideally, prenatal vitamins should be started 1–3 months before conception. Nutrients such as folic acid help support early fetal development and may reduce the risk of certain birth defects that occur in the first few weeks of pregnancy.

During Pregnancy
As your baby grows, your nutritional needs increase. Prenatal vitamins help provide important nutrients such as folate, iron, iodine, vitamin D, and vitamin B12 to support both maternal health and fetal development.

After Pregnancy
Many healthcare providers recommend continuing prenatal vitamins while breastfeeding. Pregnancy and childbirth can deplete nutrient stores, and breastfeeding increases the demand for several vitamins and minerals. Continuing a prenatal vitamin may help support both maternal recovery and your baby’s nutritional needs.

While prenatal vitamins are an important supplement, they work best when combined with a balanced diet and healthy lifestyle.

If you are planning a pregnancy, currently pregnant, or postpartum, speak with your healthcare provider about which prenatal supplement is right for you.