Swelling is the commonest reason, and usually harmlessStrong evidence
"It's normal to get some swelling in pregnancy, particularly in your legs, ankles, feet and fingers", the NHS says. It is often worse at the end of the day, in hot weather and later in pregnancy, because the body holds more water and the growing womb presses on the veins of the legs, and swelling that comes on gradually isn't usually harmful to you or your baby.
No study opened for this guide measured ankle pain in pregnancy on its own. About 4 in 10 women had foot swelling late in pregnancy in one study of 88 women in Taiwan; there is no large study of how common it is.
Sources 1, 2, 3
Swelling that isn't normal: pre-eclampsia and clotsStrong evidence
"A sudden increase in swelling can be a sign of pre-eclampsia or a type of blood clot called deep vein thrombosis (DVT) and needs to be checked immediately", the NHS says. Pre-eclampsia is most likely from 20 weeks and can start in the days or weeks after the birth. It is mostly found by the blood pressure and urine checks at every antenatal appointment, which is why each one matters; swelling isn't part of how the National Institute for Health and Care Excellence (NICE) defines it.
Clots are 4 to 6 times more likely in pregnancy, but still affect only about 1 to 2 in 1,000 pregnancies and the weeks after the birth, most often just after delivery, the Royal College of Obstetricians and Gynaecologists (RCOG) says. In pregnancy they are usually in the left leg (88% of the 96 women whose side was known, in a review of 6 studies) and often high in the leg, so the whole leg may swell.
Sources 4, 5, 6, 7, 8, 9, 10
Looser joints, but no sign of more sprainsEmerging evidence
Joints do loosen a little in pregnancy: looseness rose in 5 of 7 joints in one small study and in the wrists of 19 of 35 women in another, but it didn't go up and down with relaxin, the hormone usually blamed, and its effect in pregnancy is still debated.
No study has compared ankle sprains in pregnant and non-pregnant women. In 1,469 pregnant women in North Carolina, injuries from physical activity were rare (3.2 per 1,000 hours of activity), more than half were bruises or scrapes, two-thirds happened in everyday activity rather than exercise, and most came from falls.
Sources 11, 12, 13, 14
Falls are the bigger riskEmerging evidence
About 1 in 4 women fall during pregnancy (27% of 3,997 US women, asked after the birth), 56% of falls were indoors and 39% on stairs, and women aged 20 to 24 fell more than women over 35. Standing balance was worse from the second trimester in some studies but not others. Pregnant women walk a little more slowly, and push off a little less from the ankle, most in the third trimester.
Sources 15, 16, 17, 18, 19, 20, 21
Changing feet, and tendons nobody has studied in pregnancyEmerging evidence
Many women's feet get a little longer and their arches drop in pregnancy: about 19 weeks after a first birth, 30 of 49 women still had slightly longer feet (mostly 2 to 10 mm). Pain along the inner ankle and arch, or at the back of the ankle, can follow, but no study has measured these tendon problems in pregnancy, and a review of foot and ankle problems in pregnancy doesn't give a figure for them.
Sources 22, 23, 24
Cramps in the calf and footStrong evidence
Leg cramps are sudden, sharp pains, usually in the calf but sometimes the foot, most often at night later in pregnancy. They last seconds to minutes, and the muscle can feel sore for up to a day afterwards. Cramps in pregnancy "should pass after the baby is born", NHS inform says.
Sources 25, 26, 27
Less common causesEmerging evidence
Hot, red, painful, swollen skin can be a skin infection (cellulitis). Rheumatoid arthritis often settles in pregnancy (in about 3 in 5 women, an Arthritis UK booklet says), but almost half flare after the birth. Temporary thinning of the ankle bones in pregnancy is very rare: 8 ankle cases have been reported. Itchy palms and soles, worse at night, aren't an ankle problem: they can be intrahepatic cholestasis of pregnancy, which is urgent.
Sources 28, 29, 30, 31
When a scan or test helpsStrong evidence
Most ankle pain in pregnancy needs no tests; the blood pressure and urine checks at antenatal appointments pick up pre-eclampsia. A suspected clot needs an ultrasound: "you should be referred to hospital within 24 hours for an ultrasound scan", the NHS says.
After an injury, an ankle X-ray can be done when it's needed. Our reading of the guidance: UK advice says the dose to the baby from any diagnostic X-ray in current use "should present no risk" of causing the baby's death, malformation, poor growth or impaired mental development, and asks about pregnancy for X-rays between the diaphragm and the knees, so the ankle lies well outside that area; a limb X-ray gives a dose of less than 0.01 millisieverts (mSv), less than a day and a half of natural background radiation. Tell the radiographer you're pregnant, and let a clinician decide whether you need one.
Sources 7, 5, 10, 32, 33, 34
How it usually goesEmerging evidence
Swelling builds towards the third trimester and "is usually temporary and settles after your baby's born", NHS inform says, though no NHS page gives a timescale; in one small US survey, most women who had swelling in pregnancy still had some after the birth. Cramps usually pass after the birth. After a sprain, most people feel better within about 2 weeks, while a broken ankle usually takes 6 to 8 weeks to heal. Foot length and arch changes can last at least 19 weeks after the birth. Pre-eclampsia and clots can start in the weeks after the birth, so the warning signs still apply then. No one can promise a timescale.
Sources 2, 35, 27, 36, 37, 22, 5, 8
