Inclusion Criteria:  Pregnant women aged between 16 and 45 years old. Women with GDM diagnosed at 26+0 to 30+6 weeks' gestation in accordance with the NICE guidelines Or Pregnant women with pre-existing type 1 or type 2 diabetes mellitus Or Women diagnosed with ICP at any stage of pregnancy Fluent in English or presence of an interpreter or translation service (i.e. telephone translation services) at all visits. Singleton pregnancy. Willing and able to give written informed consent and comply with requirements of the study protocol Planned antenatal, intrapartum and postpartum care at the participating centre (i.e. not planning to move before delivery)  Exclusion Criteria:  1. Known fetal congenital abnormality on ultrasound requiring fetal medicine input (excluding congenital heart disease).  Known fetal congenital abnormality on ultrasound requiring fetal medicine input (excluding congenital heart disease). Significant pre-pregnancy co-morbidities that increase risk in pregnancy, for example renal failure, severe liver disease, transplantation, cardiac failure, psychiatric conditions requiring in-patient admission (within previous year) in the opinion of the responsible clinician or the CI. Significant co-morbidity in the current pregnancy, nephropathy (estimated GFR <60ml/min), other physical or psychological conditions likely to interfere with the conduct of the study and/or interpretation of the study results in the opinion of the responsible clinician or the CI. (This does not include diabetes mellitus). History of bariatric surgery. Hypertension requiring treatment pre-pregnancy / in pregnancy. Prescribed other medications that affect insulin sensitivity prior to OGTT for women diagnosed with GDM (oral antihyperglycemic agents, antipsychotic drugs, supraphysiological doses of steroids). For the baby after birth: Not meeting the safety criteria to undergo MRI scan (e.g. metal implants, non MRI compatible devices, metal fragments in the body). [ The mother will not have an MRI scan].