My periods have become very light, just a day or two. Does that mean a thin lining?

Lighter periods can have many causes, and many of them are harmless. Flow naturally changes with age, stress, weight changes, intense exercise and after stopping hormonal contraception. Thyroid problems, raised prolactin and PCOS can also change the pattern. A thin lining is one possible reason, but it can't be diagnosed by flow alone. Some women with light periods have a perfectly normal lining around ovulation. A sudden or marked reduction in flow after a uterine procedure, such as a D&C after a miscarriage, a caesarean or an infection, can sometimes be linked to scarring inside the uterus (called Asherman syndrome), which is worth checking. A gynaecologist may suggest a transvaginal ultrasound around the time of ovulation to measure the lining thickness, along with thyroid and prolactin tests. If scarring is suspected, a hysteroscopy, where a thin camera looks inside the uterus, can both diagnose and often treat it. See a doctor if your periods have become much lighter quickly, especially after any procedure, if they stop altogether for three months, or if you've been trying for a year (six months if 35 or older). Note your flow pattern and any past procedures to share at the visit.

Ask whether your lining can be measured during a follicle scan near ovulation. That number tells you much more about your lining than how heavy or light the period looks.