It is ovulation and the hormone changes that subsequently follow which leads to the normal menstrual cycle. Thus, irregular periods strongly suggest that an egg is not being released each month.
Sometimes women still cycle but ovulation does not happen every month. The test for ovulation is the day 21 progesterone (for a 28 day cycle), and the term anovulation means that ovulation is not taking place.
Sometimes women don't ovulate because of an overactive pituitary gland, leading to high levels of the hormone prolactin. Bromocriptine is a drug that is used to suppress this excess and it also leads to the return of ovulation in most cases.
Polycystic Ovary Syndrome (PCOS)
Another cause of anovulation is PCOS. Hormonal problems are sometimes found and on scan the ovary has lots of small cysts around the edge. These are not harmful in themselves, just a sign that eggs have started to develop, but never got released.
Clomifene Citrate Clomid)
Commonly used to start the ovaries ovulating again. Clomid is taken on days 2-6 of a cycle and it 'kick-starts' the ovary into making and releasing an egg.
A day 21 progesterone level in the first cycle will check that it has worked, but some women need a higher dose. It is a safe drug but, as with most ovulation treatments, it increases the risk of a multiple pregnancy, such as twins. This happens in about 1 in 20 women treated with clomiphene.
A treatment that is used in PCOS where clomiphene is unsuccessful. Several small holes are made in the ovary during a laparoscopy, and this reverses the hormone problems associated with the disease.
The success rate depends on many factors, but typically around 50% of women fall pregnant within 1-2 years of treatment and by 3 years about 75% are successful.
A more intensive treatment, which uses injections of hormones on a daily basis and close ultrasound monitoring of the ovary's response. The aim is to produce several good quality eggs and time their release with intercourse.
Side effects include multiple pregnancy (10-20%), an increased risk of ectopic pregnancy and a condition called ovarian hyperstimulation syndrome, where an unexpectedly excessive response occurs and large ovarian cysts develop.
The success rates vary greatly depending on the individual situation, but 40-85% after 6 treatment cycles is typical. Success after 6 cycles is less likely, though not impossible, and IVF is usually advised if this is unsuccessful.