Uterine Contractions: Types, Characteristics and Signs

What uterine contractions are

The uterus is a hollow organ made mostly of smooth muscle called the myometrium. Like the heart, this muscle can contract on its own in waves. Hormones control how strongly and how often it does so. Oxytocin triggers contractions, prostaglandins make the muscle more sensitive, and progesterone keeps the uterus calm during most of pregnancy.

When a contraction happens, the uterus tightens and feels hard to the touch. It then relaxes and becomes soft again. During labor this rhythm pulls the cervix open (dilation), thins it out (effacement) and pushes the baby down the birth canal.

Types of uterine contractions

Braxton Hicks contractions

These "practice contractions" can start from around 16 to 20 weeks but are usually noticed in the third trimester. The belly goes hard for 30 seconds to 2 minutes, then relaxes. They are irregular, do not get stronger, and often stop when you walk, rest, change position, empty your bladder or drink water. They do not open the cervix. Dehydration, a full bladder, sex and a busy day can bring them on.

Prelabor and early labor

In the days before labor, Braxton Hicks may become more frequent and uncomfortable. Early labor contractions are mild and irregular at first, perhaps 5 to 20 minutes apart and lasting 30 to 45 seconds, then settle into a pattern.

Active labor contractions

In active labor, contractions come every 3 to 5 minutes, last 45 to 70 seconds, and are strong enough that you cannot talk through them. In transition, just before pushing, they can come every 2 to 3 minutes and last up to 90 seconds.

Menstrual contractions

During a period, prostaglandins released from the uterine lining make the muscle contract to shed it. Higher prostaglandin levels cause stronger cramps. Severe cramps that worsen over time can be a sign of endometriosis, adenomyosis or fibroids. See menstrual cramps.

Characteristics of uterine contractions

Clinicians describe contractions by four measurable features:

• Frequency: how often they come, timed from the start of one to the start of the next. In active labor this is usually every 2 to 5 minutes.
• Duration: how long each lasts, from when the tightening starts to when it fully relaxes. Labor contractions usually last 45 to 90 seconds.
• Intensity: how strong they are. At home this is judged by touch: mild contractions feel like the tip of your nose, moderate like your chin, strong like your forehead. In hospital an internal pressure catheter can measure it in mmHg.
• Resting tone: whether the uterus relaxes fully between contractions. A uterus that stays hard is a warning sign.

Doctors also look at the pattern. Tachysystole means more than 5 contractions in 10 minutes, averaged over 30 minutes. It can reduce oxygen to the baby, especially when labor is induced with medicine, so the dose is reduced or stopped.

Signs of uterine contractions in pregnancy

Contractions are not always painful. Signs include:

• The whole belly feels tight or hard, then softens
• A period-like cramp low in the belly
• A dull low backache that comes and goes in a rhythm
• Pressure in the pelvis or vagina
• Pain that starts in the back and wraps around to the front

Braxton Hicks vs real contractions

Preterm labor: contractions before 37 weeks

Preterm labor is regular contractions that open the cervix before 37 weeks. Warning signs include:

• Contractions every 10 minutes or more often
• Period-like cramps or a low, dull backache that does not go away
• Pelvic pressure, as if the baby is pushing down
• A change in vaginal discharge: watery, mucus-like or bloody
• Leaking fluid

Call your obstetric unit straight away if you notice these. Treatment can include medicines to slow contractions for a short time, steroid injections to mature the baby's lungs, and magnesium to protect the baby's brain if birth is very early.

Contractions with other symptoms

• Bleeding: light pink mucus (the "show") is normal near term. Bright red bleeding or bleeding with constant pain may be placental abruption and is an emergency.
• Fluid leaking: may mean the waters have broken. See fluid leakage.
• Reduced baby movements: always get checked the same day. See decreased fetal movement.
• Fever or painful urination: infection, including a urinary tract infection, can trigger contractions.
• Cramping in early pregnancy: mild cramping is common as the uterus grows. Cramping with bleeding can be a threatened miscarriage and needs a call to your clinician.

How contractions are timed and checked

At home, time contractions for an hour using a watch or app. Write down when each starts and how long it lasts. Many clinicians use the 5-1-1 rule for first babies at term: call when contractions are 5 minutes apart, last 1 minute, and have done so for 1 hour. If you have had a fast labor before, live far from the hospital, or your waters break, call sooner.

In hospital, a tocodynamometer (a pressure sensor on a belt) records contraction timing alongside the baby's heart rate (cardiotocography, or CTG). A vaginal examination checks whether the cervix is changing. In possible preterm labor, a swab for fetal fibronectin or an ultrasound of cervical length helps show whether birth is likely soon.

Easing contractions

In pregnancy

• Braxton Hicks: change position, rest on your left side, empty your bladder and drink water. A warm (not hot) bath can help.
• Early labor: stay at home if advised, keep moving, eat light snacks, drink fluids, and use warm showers, breathing and massage.
• Active labor: options include breathing techniques, water immersion, nitrous oxide, opioid injections and epidural anesthesia.
• Acetaminophen (paracetamol) is generally considered safe in pregnancy at the label dose. Avoid ibuprofen and other NSAIDs in pregnancy unless your clinician advises them, particularly from 20 weeks.

Period cramps

• Heat on the lower belly or back
• Ibuprofen or naproxen, started at the first sign of cramps and taken at the label dose, block prostaglandins. Avoid them with stomach ulcers or kidney disease
• Regular exercise
• Hormonal contraception, which reduces cramps for many people

Frequently asked questions

What are the characteristics of uterine contractions?

Contractions are described by frequency (how often), duration (how long each lasts), intensity (how strong) and resting tone (whether the uterus relaxes between them). In active labor, contractions typically come every 3 to 5 minutes, last 45 to 70 seconds, and the uterus softens fully in between.

What are the types of uterine contractions?

The main types are menstrual cramps, contractions after orgasm, Braxton Hicks practice contractions in pregnancy, preterm labor contractions before 37 weeks, true labor contractions, and afterpains following birth. They differ in timing, regularity and strength, and only labor contractions open the cervix.

What are the signs of uterine contractions?

The belly tightens and feels hard, then softens. You may feel a period-like cramp, a dull low backache that comes and goes, or pressure in the pelvis. Labor contractions become regular and stronger, and are often accompanied by a bloody show or waters breaking.

How do I know if contractions are real labor?

Real labor contractions follow a regular pattern and get longer, stronger and closer together over time. They continue when you rest, walk or change position. Braxton Hicks contractions are irregular, stay mild, and usually fade with rest, a change of position or a drink of water.

Can you have uterine contractions when not pregnant?

Yes. The uterus contracts during every period, which causes menstrual cramps, and briefly after orgasm. Strong, painful contractions outside pregnancy can be linked to endometriosis, adenomyosis or fibroids, especially if they worsen over time or come with heavy bleeding.

How many contractions per hour is normal in pregnancy?

A few irregular Braxton Hicks tightenings an hour can be normal in the third trimester, especially in the evening or after activity. Before 37 weeks, 4 or more contractions in an hour that do not settle with rest and fluids should be checked the same day for preterm labor.