A number of hormones affect the reproductive tract. Getting pregnant requires that the delicate balance of hormones is intact; any disturbance in the hormone balance can result in menstrual difficulties that prevent pregnancy. The menstrual cycle depends on a balance of estrogen, a form of estradiol, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and progesterone, as well as other hormones
Amenorrhea means an absence of periods. When you're not having any periods, the balance of hormones is usually upset. Several types of hormone imbalance can cause amenorrhea. High FSH levels (usually due to premature ovarian failure), menopause or perimenopause--the period several years before menopause--can cause amenorrhea. Low estrogen levels often accompany high FSH levels and can also lead to lack of menstrual periods. High levels of prolactin, a hormone produced by the pituitary during lactation, can also be caused by pituitary tumors (among other causes) and can cause amenorrhea, according to the National Endocrine and Metabolic Diseases Information Service.
Short Menstrual Cycles
Because menstrual cycles usually consist of approximately 14 days of follicular or egg development and 14 days of luteal phase, or post-ovulatory phase, anything that shortens either phase can result in periods that are unusually close together. Periods that occur closer together than 28 days may be due to high estrogen levels. These result in an egg being produced early in the menstrual cycle, before Day 14. Short cycles can also be related to low progesterone levels after ovulation, a condition known as luteal phase defect, or LPD. Low progesterone levels may not maintain the uterine lining after ovulation for a full 14 days, according to Georgia Reproductive Specialists.
Long Menstrual Cycles
Long menstrual cycles, or periods that are further apart than every 35 days, may be caused by polycystic ovary syndrome or PCOS. PCOS is caused by an increased level of the male hormones (androgens), according to the Mayo Clinic, and an imbalance in the ratio of LH to FSH, which is normally 1:1 but changes to 2:1 in PCOS. PCOS can also cause heavy periods.
Low levels of the hormone LH can result in a syndrome called luteinized unruptured follicle, or LUF. In LUF, an egg develops in a follicle but the LH doesn't rise high enough to cause release of the egg, resulting in a lack of ovulation (anovulation), according to Georgia Reproductive Specialists.
Physical symptoms of hormone imbalance depend on what type of imbalance is present. Women with PCOS have excess hair, are more likely to have diabetes, and also more likely to be overweight. High prolactin levels can cause galactorrhea, or leaking milk.