What it isStrong evidence
The pelvis is a ring of bones joined by the two sacroiliac joints at the back and the symphysis pubis at the front. PGP is pain in and around these joints in pregnancy or after birth. The NHS describes pain over the pubic bone at the front in the centre, across one or both sides of the lower back, in the area between the vagina and anus, and spreading to the thighs, sometimes with clicking or grinding. SPD is the old name; PGP is now the umbrella term.
A European guideline defines it as pain between the top of the back of the pelvis and the fold of the buttock, especially near the sacroiliac joints, with or without pain at the front. It notes that PGP shortens how long you can stand, walk and sit.
Sources 1, 2, 3, 4
Why it happensEmerging evidence
Usually a mix of things: the pelvic joints moving unevenly, changes in how the tummy, hip, back and pelvic floor muscles work, an old injury, and sometimes the baby's position. The Pelvic, Obstetric and Gynaecological Physiotherapy group (POGP) says only a small number of women have pain caused by pregnancy hormones.
A Cambridge NHS leaflet adds that the pelvis remains strong and stable in pregnancy and birth, and that pregnancy can turn up the volume on the nervous system, so pain can feel stronger. The causes are still debated.
Sources 2, 5, 4
Who gets itStrong evidence
Up to 1 in 5 pregnant women, to some degree. In three large studies that confirmed it by examination, 16% to 20% of pregnant women had it at any one time, and POGP's guidance for professionals puts severe pain and disability at 5% to 8%. It often starts around 18 weeks and peaks between 24 and 36 weeks, though it can start at any point in pregnancy or in the weeks after the birth.
Risk factors include earlier low back or pelvic pain, a previous pelvic injury, PGP in an earlier pregnancy, a physically demanding job, having had more than one baby, being overweight and very flexible joints (hypermobility). The contraceptive pill, height, smoking, age, breastfeeding and the time since your last pregnancy don't seem to matter.
Sources 1, 3, 4, 6, 7, 8, 2
How it differs from back pain in pregnancyEmerging evidence
A systematic review found that PGP and pregnancy low back pain behave as two separate problems. Of all back and pelvic pain in pregnancy, about half is PGP, a third is low back pain, and a sixth is both. Where it hurts is the main clue: PGP sits below the top of the back of the pelvis, in the buttock or at the pubic bone, while low back pain sits higher, in the spine. PGP is brought on by standing on one leg, turning over in bed, stairs and moving the legs apart.
Having both is the hardest: in a Swedish study of 313 pregnant women, those with both had the worst pain, function and health. The NHS back pain in pregnancy page covers back pain on its own.
Sources 9, 4, 10, 1, 2, 11
How it's recognisedStrong evidence
The Royal College of Obstetricians and Gynaecologists (RCOG) says to tell your midwife or doctor about your pain, and that you should be offered an appointment with a physiotherapist. Diagnosis is by examination: the European guideline recommends pain provocation tests, such as pressing along the thigh with the hip bent (the thigh thrust test), and a test of lifting a straight leg while lying down. It doesn't recommend X-rays or other scans to diagnose PGP, and keeps magnetic resonance imaging (MRI) for warning signs.
A clinician will also think about a urine or other infection, a problem in the lower back, and tightenings or early labour.
Sources 3, 4, 6
What scans mean, and separation of the jointEmerging evidence
The summary of a StatPearls chapter (an online medical reference) says the joint at the front normally widens a little in pregnancy, by 2 to 3 mm, that a gap of more than 1 cm is considered abnormal, and that true separation around the birth is rare, at 1 in 300 to 1 in 30,000 births. Separation shows up as severe pain and difficulty walking within hours to days of the birth. Otherwise, scans are rarely needed; if pain isn't settling after the birth despite physiotherapy, an X-ray standing on one leg, an ultrasound or an MRI may be considered.
POGP lists 'split pelvis', 'separated or displaced joints' and 'dislocated pelvis' among the misleading terms that add to anxiety. A Cambridge NHS leaflet puts it plainly: the pelvis remains strong and stable.
Sources 12, 2, 6, 5
How it usually goesEmerging evidence
POGP says that with the right advice early, it can usually be managed well, and having some symptoms doesn't mean you'll automatically get worse. Some women find it very hard: in one analysis, 8% of women with pregnancy back and pelvic pain were severely disabled.
After the birth it usually settles quickly: about 7% still have it in the first 3 months. In a Danish study of women with PGP confirmed by examination, 62.5% were pain-free within a month of the birth and 8.6% still had pain at 2 years. Those with pain only at the front had all recovered by 6 months, while 21% of those with pain in all three joints still had it at 2 years. RCOG says around 1 in 10 women have ongoing pain. It often comes back in a later pregnancy, though not necessarily as badly.
Sources 2, 9, 4, 13, 3