Heavy periods that leave you drained. A thyroid problem that runs in the family. Night sweats at 47 and a friend who swears by a hormone test. Or a plan to start a family next year. Women's health blood tests come up for very different reasons at different ages, and the useful tests are not always the ones people expect. This guide walks through the common ones, what each marker means and where UK guidance says a test does, or does not, help.
Why women's health blood tests change through life
Periods, pregnancy and menopause all shape what the body needs. Iron is lost every month with menstrual blood. The thyroid is more likely to slow down in women than in men. Vitamin D runs low for many people in UK winters, and vitamin B12 matters more on a plant-based diet. Then, around the mid-forties, hormones start to shift, and this is where people are often surprised: for most women over 45, a blood test is not needed to recognise perimenopause.
So a good check-up starts with your situation (your periods, your symptoms, your plans) rather than with the longest list of tests.
Iron, ferritin and heavy periods
Iron deficiency is one of the most common nutritional problems in the world, and women of reproductive age are among the groups most affected, largely because of menstrual blood loss (Pasricha et al., 2021). It can cause tiredness, breathlessness, headaches and hair shedding long before anaemia shows up on a blood count.
The NHS says that if you see a GP about heavy periods, you may have blood tests to check for underlying conditions such as iron deficiency anaemia. Ferritin, the protein that stores iron, is the marker that shows how full your stores are; a full blood count shows whether haemoglobin has already dropped. The NHS describes periods as heavy if, for example, you need to change a pad or tampon every 1 to 2 hours or pass clots larger than about 2.5cm. That is a reason to see your GP, not only to test.
Thyroid
An underactive thyroid is common and often creeps in slowly: tiredness, feeling the cold, weight gain, dry skin, low mood, or periods that become irregular or heavier. In the UK, the main cause is Hashimoto's disease, an autoimmune condition that is most common in women and usually starts between 30 and 50 (NHS). The usual first test measures thyroid stimulating hormone (TSH) and free thyroxine (free T4). Thyroid antibodies can show whether the immune system is involved, which is useful context for your GP.
Vitamin D and vitamin B12
Between October and early March, the UK sun is too weak for the skin to make vitamin D, and the NHS advises everyone, including pregnant and breastfeeding women, to consider a daily 10 microgram supplement in autumn and winter. Vitamin B12 comes mainly from meat, fish, milk and eggs, so it is particularly worth checking if you eat a vegan or mostly plant-based diet. Folate is often measured alongside it, because the two work together to make healthy red blood cells.
Perimenopause and menopause: when a test helps
This is the area with the most confusion. NICE guidance (NG23) says that in otherwise healthy women aged 45 or over with menopause symptoms, perimenopause and menopause should be identified without laboratory tests: perimenopause from symptoms such as hot flushes together with changes in the menstrual cycle, and menopause after 12 months without a period when not using hormonal contraception. NICE also advises against using tests such as anti-Müllerian hormone (AMH) or oestradiol for this purpose at 45 or over.
A follicle stimulating hormone (FSH) test has a narrower place. NICE says it may be considered between 40 and 45 with symptoms and a change in periods, and under 40 when early menopause is suspected, and that it should not be used while taking combined hormonal contraception or high-dose progestogen. Hormone levels swing from day to day in perimenopause, which is why a single result can mislead.
That does not make blood tests pointless in your forties and fifties. Menopause is a good moment to look at cholesterol, blood sugar, vitamin D and thyroid, because symptoms overlap and heart health matters more after it. Our menopause page explains which tests people choose and why.
Planning a pregnancy
The NHS advises taking 400 micrograms of folic acid every day while trying to conceive, ideally from 3 months before, and for the first 12 weeks of pregnancy. A Cochrane review found that taking folic acid around conception lowers the chance of neural tube defects such as spina bifida (De-Regil et al., 2015). The NHS also recommends a daily vitamin D supplement during pregnancy.
Immunity is the other thing worth checking early. The MMR (measles, mumps and rubella) vaccine cannot be given during pregnancy, and the NHS says 2 doses give long-term protection. Routine rubella screening in pregnancy ended in England in 2016 (Public Health England), so before trying is the time to check your vaccination record with your GP surgery or, if it is unclear, your immunity. Our planning a baby page covers the rest.
