What Triggers Labour to Start?

Pregnancy is a long process, but it all comes down to one important final event: labour. So what triggers labor to start? Current understanding points to a combination of factors working together: hormonal changes in both mother and baby, signals from the placenta, the natural ripening and softening of the cervix, a rise in inflammation, and the baby reaching a stage of readiness for life outside the womb. Together, these processes are believed to trigger the contractions that bring on labour, though the exact biological switch that decides the precise moment is still not fully understood, even by medical science.

As you reach late pregnancy, around 37 to 40 weeks, it is natural to start wondering what causes labour to start and to watch closely for the first signs. Understanding what makes labor start, and recognising the early signs of going into labour, can help you feel more prepared for what is ahead.

In this article, we explain what happens in your body before and during labour, including the hormones and processes involved, the common early signs, and what to expect at each stage, so you can feel ready and informed for the final stage of pregnancy.

Key takeaways

• Labour is believed to begin through a combination of hormonal shifts, placental signals, cervical changes, and the baby's readiness for birth.
  
• The exact biological trigger that decides the precise moment labour starts is still not fully understood.
  
• Term labour can happen any time between 37 and 42 weeks, so a due date is only an estimate.
  
• Early signs include Braxton Hicks contractions, a softening cervix, and the release of the mucus plug.
  
• Labour is only considered to have started once contractions become regular and the cervix begins to dilate
  

What Happens in Your Body Before Labour Starts

While you may be looking at your due date, 40 weeks after your date of conception, as something concrete, it really amounts to little more than an educated guess. In reality, term labour can happen anytime between 37 and 42 weeks. In fact, nearly a third of women don’t give birth within ten days of their expected due date, and only about five percent of babies are born on their actual due date.

So what exactly goes on in your body in those last few weeks that determines the onset of labor? What causes labor to start? The answer lies in a complex mix of hormonal changes, your baby’s readiness, and physical changes in your body. As your baby matures and signals that it’s ready for life outside the womb, your body begins to respond. Hormones like prostaglandins help soften and thin the cervix, while oxytocin triggers the contractions that eventually lead to labour.

Here are just a few signs your body is getting ready for labour.

Braxton Hicks Contractions Can Start Even Weeks Before Labour

Firstly, weeks or days before your delivery, you’ll probably start having something called Braxton Hicks contractions. These are not the real contractions that push the baby out during labour. Instead, they help your body prepare for the real thing. It’s essentially your uterus tightening and relaxing as it gets ready for birth. They are usually painless, though some women mistake them for true contractions, which is why they’re often called “false labour.” Unlike real contractions, they don’t lead to the onset of labor because they don’t cause the cervix to open.

Your Cervix Will Get Thinner and Softer

Speaking of your cervix, it also goes through important changes right before labour. As part of the hormonal process that causes labor to start, your cervix begins to soften, thin out, and prepare to open. This process, driven in part by prostaglandins, is essential for labour to progress.

You may also notice something called a show, which is the mucus plug being released. It often appears as a pinkish or blood-streaked discharge. While it’s not exactly pleasant, it’s a normal sign that your body is preparing for the onset of labor.

Signs of Going Into Labour 

In the days or hours before labour, your body may show early signs. Many parents wonder how do contractions start and notice them first as mild, irregular tightening of the uterus. You might also experience your water breaking, lower back pain, a bloody show, or cervical dilation as your body prepares for birth. Recognizing these signs of going into labor can help you know when it’s time to head to the hospital or birth center.

Other Signs of Your Body Getting Ready for Labour

• Cramping

• Loosening of joints

• Having diarrhoea, as your rectum is one of the pelvic muscles that loosens pre-labour

• Many women also report the phenomenon of nesting, or the desire to clean and organise in preparation for their baby’s arrival

• Lightening, which is when you suddenly have more room to breathe before labour. This happens because your baby engages or shifts further down your pelvis so that its head is facing toward your cervix in preparation to come out of the birth canal

Discover our toolkit for labour, where we discuss everything from creating a birth plan and packing your hospital bag to understanding the different types of births, pain relief options, and the role of partners.

How does labour start?

While all of the above early signs of labour can occur days and even weeks before you give birth, there are other symptoms that occur hours before labour that are even more useful as signs that labour has started. One of the best-known ones is when your “water breaks,” which usually happens no more than 24 hours before you go into labour.

Listen to conversations about birth experiences for more personal stories and insights on what it feels like to go into labour.

What Happens When Your Water Breaks?

Well, when your baby develops inside your womb, it lives in a bag of fluid, your amniotic sac. When your baby is ready to emerge, that sac will break, and all of the fluid will have no place to go other than to come out of your vagina. But it’s not always the dramatic event you see in movies. Sure, it may come out in a big rush, but it also may just trickle. And there’s a chance it won’t even happen at all and that your baby will be born still in the amniotic sac. That’s why you can’t rely on your water breaking as the only surefire sign that you’re going into labour.

You'll Know Labour Has Started When You Experience Regular Contractions

The only true symptoms of going into labour are the ones that are used to define the beginning of labour: having contractions. This is when your body works to open up your cervix so that your baby can come out. This happens when your uterus presses down on your baby, whose head then presses down on your cervix. This, and the release of the hormone oxytocin, will trigger contractions.

Contractions will probably feel like physical discomfort, dull aches, and pressure in your pelvis, back, and lower abdomen. A lot of women compare them to strong period cramps. Toward the beginning of labour, they’ll start out as weaker, shorter, and farther apart from one another. As you get closer to giving birth, they’ll become longer, stronger, and more frequent.

The Three Stages of Labour

Stage 1: Early Labour and Active Labour

Stage 1 consists of two steps: Early labour and active labour.

Early Labour Lasts from Hours to Even Days

The phase when your cervix dilates from zero to six centimetres is called early labour and it can last for quite a long time, as long as hours or even days. During early labour, your contractions will be mild and irregular at first and then progressively become more intense and frequent. Even though you may want to head to the hospital immediately, many doctors recommend staying at home during early labour, where you’ll be more comfortable and are less likely to need medical intervention.

During Active Labour, Contractions Feel More Intense

After your cervix expands to six centimetres, you’ll reach what is called active labour, when your cervix dilates from six to ten centimetres. During this stage, your contractions will come every three to four minutes, will last around 60 seconds each, and will feel much more intense and uncomfortable, to the point that it’ll be difficult not to focus on them. At this stage, you’ll want to head to your birthing place, whether that be the hospital or just a prepared birthing area in your home. Active labour will generally last between four to eight hours.

Transition is the last and most intense part of early labour, right before you start pushing. Contractions come close together, often every two to three minutes, and can last 60 to 90 seconds. Many women feel it's the hardest part of labour, but it's usually also the shortest, often lasting from a few minutes up to an hour.

Stage 2: Pushing and Birth

Stage 2 of labour will be when you actually deliver your baby, which includes all of that pushing you hear so much about. This can take anywhere from a few minutes up to a few hours, though you can expect it to take longer if you’re giving birth for the first time.

Stage 3: Delivering the Placenta

Unfortunately, stages 1 and 2 are not the end of labour. In stage 3, you’ll deliver the placenta, which can take anywhere from five minutes to an hour. You’ll continue to have contractions and will need to push again in order to get the placenta out. After that, your uterus will immediately continue to contract in order to get back to its normal size. It’ll take up to six weeks for this process to be completely finished.

Learn more: Postpartum - A survival guide for the fourth trimester.

Learn more about C-section birth: What dads and partners need to know

Hormones Released During Labour

Just like with every part of pregnancy, there are a lot of hormones at play in the labour process.

• Oxytocin: It is often known as the cuddle hormone, as it is released when people snuggle up or bond. Oxytocin also plays a role in labour, as it can act as a contraction trigger (and also the letdown of your breast milk).

• Relaxin: This hormone is the reason for the loosening of your cervix, joints, and bowels, which comes along with labour. Learn more about pregnancy hormones.

• Prostaglandin: Helps open the cervix and allows the body to be more receptive to oxytocin.

• Beta-endorphins: A type of endorphin that not only helps with pain relief but also creates feelings of joy and euphoria. Beta-endorphins also slightly suppress your immune system so that it doesn’t overreact to the “foreign object” that is your baby.

• Epinephrine and norepinephrine: Also known as adrenaline and noradrenaline, which you might know as the fight-or-flight hormones. Typically associated with stress, a rise in epinephrine increases your levels of prostaglandin and cortisol, which stimulate contractions and help give you the energy to push during stage 2 of labour.

Learn more about pregnancy hormones; Why do they always seem to be all over the place?

What Triggers Labour?

All this useful information aside, you might still be wondering: does your body or the baby decide when labour starts? Or what hormone does the baby release to start labour? The truth is that the precise cause of labour remains one of the many medical mysteries that scientists continue to study. While we may not have all the answers, we have listed a few theories that provide some fascinating insights into the labor process and the onset of labor.

The Role of Placental CRH in Triggering Labour

One area researchers focus on closely is placental corticotropin-releasing hormone, or CRH. Unlike most hormones in pregnancy, CRH is produced by the placenta itself, and levels rise steadily as pregnancy progresses toward term, then increase sharply in the final weeks before birth. Some researchers describe this rising pattern as a kind of placental clock, helping to time the onset of labour.

CRH is thought to interact closely with the baby's own cortisol levels. As the baby's system matures, it produces more cortisol, which in turn stimulates the placenta to release even more CRH. This feedback loop is believed to help ripen the cervix, increase the sensitivity of the uterus to oxytocin, and support the hormonal cascade that leads to contractions. While CRH is not the sole answer to what triggers labour, it is one of the more well-studied pieces of the puzzle.

Hormonal Triggers

One of the key theories about what initiates labour revolves around hormonal changes. As the pregnancy progresses, the hormone progesterone helps maintain the uterine lining, preventing contractions. However, as the pregnancy nears full term, hormone levels drop, triggering a set of events which prepare the uterus for labour. This shift allows the uterus to contract and helps set the stage for delivery. Hormones released by the baby, such as cortisol, may also play a role in signalling the body to initiate labour.

Physical Factors

Physical developments within the baby’s body may also influence the start of labour. For instance, telomeres, which are a part of our DNA associated with aging, are present in higher quantities in the amniotic fluid as labour begins. Researchers believe this might signal to the baby that it’s time to be born. Similarly, the development of the baby’s lungs is critical. Around 32 weeks, the lungs produce surfactant protein (SP-A), which not only prepares the baby to breathe after birth but also activates immune cells in the uterus. These immune cells trigger an inflammatory response that could help initiate labour.

Emotional and Psychological Influences

While the physical and hormonal factors are significant, emotional and psychological aspects can’t be overlooked. Stress, relaxation, and the mother’s overall emotional state can impact hormone levels, such as oxytocin, which plays a crucial role in uterine contractions. A calm and supportive environment may aid the natural progression of labour, although it’s still largely influenced by the body’s internal processes.

Well, the potentially disappointing truth is that the precise cause of labour is one of the many medical mysteries that scientists still don’t have a real answer to. The best we can do is share a few theories that scientists are considering for possible causes of labour.

Inducing Labour at the Hospital

Now, all of this science-y talk is all well and good, but you can’t exactly inject yourself with surfactant proteins if you want to induce labour. So, what can you do?

Induction rates in the UK have been rising steadily in recent years, with around one in three labours now induced. Most inductions happen because the mother is considered overdue, usually from around 41 to 42 weeks. Doctors will choose to induce labour in order to reduce risk to both mother and baby, as there is a higher chance of stillbirth and other complications if you go over 42 weeks pregnant.

• In the hospital, inducing labour is done by applying a topical form of the hormone prostaglandin to the cervix.

• If this isn’t an option because of reasons such as the mother having had prior uterine surgery, a doctor may choose to open the cervix mechanically with a catheter or graduated dilators instead.

• To encourage a woman’s water to break, a practitioner might swipe their finger along the membranes that connect the amniotic sac, which triggers the uterus to release prostaglandin, softening the cervix and causing contractions.

• If this doesn’t work, the doctor may even manually rupture the amniotic sac.

• If, after a few hours, none of these steps brings on regular contractions, doctors will typically administer Pitocin, a synthetic form of the hormone oxytocin, intravenously. This is usually successful at triggering contractions within half an hour, and these contractions are stronger, more regular, and more frequent than those that occur with natural labour.

Natural Ways to Encourage Labour 

In some situations, women may feel the urge to help things along and induce labour at home before medical induction is considered. While there are various methods people commonly turn to, it’s important to understand that most lack scientific backing and are often based on anecdotal evidence. While some women swear by these methods, there is no definitive proof that they actually work. So, if you're wondering how to bring on labour, how to start labour, how to encourage labour naturally or how to start contractions after water breaks, here are a few methods commonly tried: 

• Moving around:  Light activities like walking or climbing stairs are thought to help your baby drop further into your pelvis, potentially encouraging the start of labour and helping to start contractions.

• Having sex: Sex can stimulate the uterus and trigger the release of oxytocin, both of which are thought to help induce labour and bring on contractions. Semen also contains prostaglandins, which might affect the cervix.

• Membrane sweep: A healthcare provider can gently separate the membranes from the cervix, which may release prostaglandins and help bring on labour.

• Relaxation: Techniques like deep breathing, prenatal yoga, or meditation can reduce stress and support your body’s natural readiness for labour.

• Acupuncture: When performed by a trained professional, acupuncture may stimulate uterine activity and help encourage contractions.
  
• Nipple stimulation: Gently stimulating the nipples, by hand or with a breast pump, encourages the release of oxytocin, the hormone responsible for contractions. Some research suggests it may help bring on labour when the body is already close to ready, but it's only recommended once you're full term and with your midwife's approval.

Ultimately, whether you choose to try to induce labour at home, use these ways to bring on labour, or wait for it to happen naturally, it’s important to carefully consider your individual situation and consult with your healthcare provider.

How to Start Contractions Naturally?

Braxton Hicks tighten your uterus but don't open your cervix, so if you're looking at how to start contractions naturally, what you actually want is contractions that build in strength and gradually dilate the cervix. Of the methods people try, nipple stimulation has some of the better evidence behind it. Stimulating the nipples, by hand or with a breast pump, encourages the release of oxytocin, the hormone responsible for contractions. A Cochrane review of several small trials found it was linked to more women going into labour within 72 hours, though it's only recommended once you're full term and with your midwife's approval.

How to Start Contractions After Water Breaks

If your waters break before contractions start, this is a different situation to simply trying to bring on labour. The risk of infection rises the longer things are delayed, so contact your midwife or doctor promptly rather than trying home remedies and waiting to see what happens. They'll guide you on timing based on your individual circumstances.

When to Contact Your Doctor

Contact your doctor if you notice reduced baby movement, your water breaks without contractions, or you have vaginal bleeding. These can signal complications and need medical evaluation.

Can You Induce Labour at 37–39 Weeks?

37 Weeks
At 37 weeks, babies are early term, so doctors usually recommend waiting for natural labour. Many wonder how to induce labor at 37 weeks, but any attempts should be discussed with your healthcare provider.

38 Weeks
By 38 weeks, babies are fully developed, though most doctors still prefer natural onset. Parents often search for 38 weeks pregnant how to bring on labour, and some natural methods may be considered safely.

39 Weeks
At 39 weeks, labour is full term and medical induction may be offered. Searches include how to speed up labor at 39 weeks and 39 weeks pregnant induce labor. Always consult your doctor before trying to bring on labour.

Common Myths About Labour Triggers

When it comes to labour, there are many myths floating around. From spicy foods to bizarre old wives’ tales, it can be hard to know what to believe. Let’s clear up some of the most common misconceptions with the facts:

Myth: Eating spicy foods induces labour
Reality: There’s no evidence to support this. While spicy foods might cause indigestion, they won’t kick-start contractions.

Myth: Walking a lot speeds up labour
Reality: Staying active is great for overall health, but there’s no proof that walking can trigger labour to start.

Myth: Castor oil induces labour
Reality: Castor oil may upset your stomach and cause diarrhea, but its effects on inducing labour are uncertain.

Myth: A full moon causes more births
Reality: It’s a fun idea, but studies show no link between moon phases and childbirth rates.

Myth: Pineapple softens the cervix
Reality: Pineapple contains bromelain, but not in large enough amounts to make an impact on labour.

Labour begins when your body and baby are ready. No shortcuts or old wives’ tales can change that. Keep calm, and trust the process.

Recover Better After Childbirth

No matter how you gave birth, the first six weeks postpartum are considered a recovery period. Your body has been stretched and stressed to the max and needs a chance to regroup. Keep in mind that every new mum is different, so every woman will recover at a different rate with different postpartum symptoms.

After birth, your stomach muscles are separated and much weaker. The gentle compression of a postpartum belly wrap encourages your muscles to push together, activating your deep core muscles, healing your tummy pouch, and avoiding long-term complications. Learn more about the Lola&Lykke Postpartum Support Band for better recovery.

Every recovery looks different, whether you're managing pregnancy aftercare or starting your breastfeeding journey. If you have more questions about childbirth, pregnancy, or postpartum care, visit our free consultancy service - Ask Lola&Lykke Experts. Your safe and non-judgemental support platform.

FAQ

How can I bring on labour fast?

Some natural methods may help jumpstart labor, such as gentle walking, nipple stimulation, or sexual activity. Always consult your doctor before trying anything.

Can orgasm bring on labour?

Yes, orgasm can release oxytocin, which may help kickstart labour, but results vary.

What helps you go into labour tonight?

There are no guarantees, but ways to go into labor now can include movement, relaxation techniques, or professional methods like a membrane sweep.

How do contractions start?

Contractions begin as your uterus responds to hormonal signals, gradually increasing in intensity and frequency.

Can walking start labour?

Walking and gentle movement can encourage the baby to move into position and sometimes help bring on labour.

What causes you to go into labor?

Going into labour is not usually caused by one single event. It is the result of several processes lining up together: falling progesterone levels, rising oxytocin and prostaglandins, a softening cervix, and signals from the baby that its lungs and other systems are ready for birth. When enough of these changes happen together, the uterus begins to contract regularly and labour begins.

What makes labor start?

Most researchers believe labour starts once a threshold of hormonal and physical readiness is reached, rather than a single trigger. As prostaglandins and oxytocin rise and the cervix softens, the uterus becomes more sensitive to contracting, and the process builds from irregular tightening into the regular, strengthening contractions of established labour.

What hormone triggers labor?

No single hormone is solely responsible, but oxytocin plays the most direct role, as it is the hormone that causes the uterus to contract. It works alongside prostaglandins, which help ripen and open the cervix, and falling progesterone, which removes the hormone that had been keeping the uterus relaxed throughout pregnancy.

Does the baby trigger labour?

There is growing evidence that the baby plays an active role. As the baby's lungs mature, they release a protein called surfactant, which appears to trigger an inflammatory response in the uterus that may help bring on labour. Rising fetal cortisol is also thought to influence placental hormone production, suggesting the baby's own readiness for birth may help signal when labour begins.

Why doesn't labour always begin at 40 weeks?

A due date is only an estimate based on averages, not a fixed deadline. Term labour is considered normal any time between 37 and 42 weeks, and only around five percent of babies are born on their exact due date. Every pregnancy reaches the right combination of hormonal and physical readiness at a slightly different time.

Can labour begin without contractions?

Labour is defined by the presence of regular, strengthening contractions that open the cervix, so contractions are a defining feature rather than an optional part. However, other signs, such as waters breaking or the release of the mucus plug, can occur before contractions properly start, which sometimes leads people to feel labour has begun before contractions are established.