Progesterone

Progesterone is the hormone of the second half of your cycle. After ovulation the empty follicle turns into the corpus luteum, and that makes progesterone for some ten to twelve days. The hormone prepares the lining of the womb for a fertilised egg, raises your body temperature by a few tenths of a degree and makes you a little sleepier and calmer. If there is no pregnancy, the corpus luteum breaks down, progesterone falls away and menstruation begins. That makes progesterone the most honest witness of ovulation. Oestradiol can rise without ovulation following; progesterone only rises if it has happened. A measurement about a week after the presumed ovulation, around day 21 in a four-week cycle, therefore answers one question very precisely: was there an ovulation this cycle? Your report shows progesterone in nmol/L, and in women with a range per phase: almost zero in the first half and after the menopause, a multiple higher in the second half. In pregnancy it climbs further, because the placenta then takes over production. In men it is a by-product of the adrenal glands and the testes, low and rarely worth measuring.

For anyone who wants to stay healthy, progesterone says one thing no other value says: whether your cycle has an ovulation. A cycle can look regular and still run without ovulation, and that is one of the first things to happen with eating too little for what you burn, training a lot, losing weight fast or lasting stress. Periods then sometimes simply keep coming, but the ovulation and the progesterone behind it stay away. In PCOS too, ovulation often fails to occur. That is more than a fertility question. A cycle with ovulation means months of oestradiol and progesterone both, and the two together protect bone and vessels and keep sleep and mood in balance. Women who menstruate for years without ovulating miss the progesterone without noticing, and build less bone than they could. With a wish for children the question is more direct: is there an ovulation, and is the corpus luteum strong enough? A progesterone in the second half that falls within the luteal range confirms both. If it stays low, the question is why, and that almost always starts with timing: drawn too early or too late, or a cycle longer than assumed. After the menopause progesterone is low, and that is the reason anyone using oestrogen as hormone therapy then usually also gets progesterone: it protects the lining of the womb against oestrogen on its own.

A high progesterone in women is almost always the ordinary picture of the second half of the cycle: after ovulation the value belongs a multiple higher than before, and setting a value from those days against the range of the first half turns a normal level into an abnormality. In pregnancy it climbs further. Genuinely too high is rare outside those two, and then it is progesterone from outside, from capsules or pessaries in fertility treatment or hormone therapy, or a rare adrenal condition. A low progesterone is the rhythm itself in the first half of the cycle and after the menopause. In the second half it is the signal: then there was no ovulation, or too recently, or the corpus luteum makes too little. The usual causes are timing, a cycle without ovulation from an energy deficit, overtraining, weight loss or stress, PCOS, and the years before the menopause, in which cycles run without ovulation more and more often. The pill suppresses ovulation and so progesterone of your own; that low number is then the intention. The lever with a cycle without ovulation is rarely the hormone itself and almost always the energy balance: enough food for what you train, with enough carbohydrates and fat, fewer training hours or more rest between them, more sleep, and gradual rather than fast weight loss. Count on months. In PCOS losing weight around the middle and less sugar and fast carbohydrates work, because insulin resistance sits beneath the missing ovulation. Progesterone as a medicine is there for anyone wanting to become pregnant after a confirmed shortfall and for anyone using hormone therapy, and that belongs with a doctor. Read progesterone beside the cycle day, always. Then beside oestradiol, which carries the first half, LH, which shows the surge just before ovulation, and with a missing cycle beside FSH. One measurement on the wrong day says nothing; one measurement on the right day says exactly one thing.