To Establish Whether Individuals With Premenstrual Dysphoric Disorder (PMDD) Demonstrate a Different Luteal-phase Sex Hormone Profile and Ratio Compared With Asymptomatic Controls.

Inclusion criteria * Aged 18-45 years old (adults but less than the typical perimenopausal age so there is not added bias/variable) * Regular menstrual cycles (21-35 days for the last 3 months) * Willing and able to complete a questionnaire (no new clinical diagnosis given) * Use home urine LH test strips to detect ovulation * Attend a single in person on site in Lancaster mid luteal blood test sample appointment (approx 7 days post LH surge) * Provide written informed consent * Have sufficient English language skills to understand the patient information * Be either in Group 1 or group 2 Group 1 (PMDD group ie case group) - self reported prior diagnosis of PMDD made by a healthcare professional (GP, psychiatrist, gynaecologist) Group 2 (Control group ie comparison group) - no prior diagnosis of PMDD made by a healthcare professional and no history of clinically significant premenstrual mood symptoms on screening Exclusion criteria * Current use or use in the last 3 months of hormonal contraception such as the combined oral contraceptive pill, the progestogen only pill, the implant, the injection, hormonal coil (Mirena, Kyleena) or patch/ring. * Current use or use in the last 3 months of any hormone replacement therapy (e.g. combined oestrogen and progesterone, oestrogen and Mirena coil combination, oestrogen alone if had a hysterectomy, or progesterone alone) or GnRH analogues use * On a selective serotonin reuptake inhibitor (SSRI) with a recent initiation or dose change within the last 3 months * Pregnant, breastfeeding or within 3 months post partum * Irregular menstrual cycles (outside the 21-35 day window) * Surgical menopause * Premature ovarian insufficiency * Other endocrine disorders e.g. uncontrolled thyroid disease, high prolactin, cushing's syndrome, polycystic ovarian syndrome) * Regular systemic steroid use or use of other medications known to affect sex hormone within the last 3 months * Severe mental health issues that impair consent or participation * Needle phobic so that venepuncture is intolerable * The use of the emergency contraceptive pill either 3 months prior to the study or during the study.