Vaginal delivery unfolds in three distinct stages, each with its own physiology and set of decisions for the birthing team. The first stage covers everything from the onset of regular contractions through full cervical dilation. The second stage is the pushing phase, ending when the baby is born. The third stage, often overlooked, is the delivery of the placenta. Understanding what happens during each stage and why certain interventions exist gives a much clearer picture of what “delivering a baby” actually involves.
The First Stage: Contractions and Cervical Dilation
The first stage of labor is the longest and does the bulk of the work. It begins when contractions become regular and strong enough to open the cervix and ends when the cervix is fully dilated to about 10 centimeters. This stage is typically split into two phases: early (or latent) labor and active labor.
During early labor, contractions are relatively mild and may be spaced 15 to 20 minutes apart. The cervix gradually softens, thins, and starts to open. This phase can last many hours, sometimes more than a day for a first-time birth. The hormonal engine behind it is oxytocin, which the body releases through a feedback loop: as the baby’s head presses against the cervix, nerve signals trigger more oxytocin release, which drives stronger contractions, which push the baby further onto the cervix. This self-reinforcing cycle is called the Ferguson reflex.1American Journal of Obstetrics and Gynecology. Physiology and pharmacology of oxytocin
The transition from early to active labor has been redefined in recent years. Older textbooks drew the line at 4 centimeters of dilation, but the American College of Obstetricians and Gynecologists now recommends that 6 centimeters be considered the start of the active phase.2Obstetrics & Gynecology. First and Second Stage Labor Management The World Health Organization’s 2018 guidelines similarly moved the threshold to 5 centimeters, and both organizations have stepped back from insisting that the cervix must open at a fixed rate of 1 centimeter per hour.3International Journal of Childbirth. Analyzing the Expectant Management of Redefined Active Phase of Labor (WHO 2018 Guidelines) in Nulliparous Women: A Randomized Control Trial That older benchmark led to a lot of unnecessary interventions, because many healthy labors simply don’t move that fast.
A systematic review of first-time mothers in spontaneous labor found that the average duration of active labor was about 6 hours, with cervical dilation averaging roughly 1.2 centimeters per hour. But the range was enormous: when the researchers looked at the slow end of normal, active labor could stretch to more than 13 hours, with dilation as slow as 0.6 centimeters per hour, and still end in a healthy vaginal birth.4PubMed Central. Active Labor Duration and Dilation Rates Among Low-Risk, Nulliparous Women with Spontaneous Labor Onset: A Systematic Review This is why current guidelines emphasize patience. A labor that is progressing slowly is not the same as a labor that has stalled.
That said, there are defined thresholds for when labor truly isn’t progressing. ACOG considers active-phase arrest to mean no change in cervical dilation in someone who is at least 6 centimeters dilated with ruptured membranes, despite 4 hours of adequate contractions or 6 hours of augmented contractions that remain inadequate.2Obstetrics & Gynecology. First and Second Stage Labor Management Reaching that point is when the conversation shifts to whether a cesarean section is warranted.
The Second Stage: Pushing and Birth
Once the cervix is fully dilated, the second stage begins. This is when you push the baby out, and it ends with birth. For first-time mothers, ACOG defines a prolonged second stage as more than 3 hours of pushing; for those who have given birth before, the threshold is 2 hours.2Obstetrics & Gynecology. First and Second Stage Labor Management
The baby doesn’t simply drop straight down. During descent, the baby’s head typically rotates. Many babies enter the pelvis facing sideways (what’s called the occipital transverse position) and then rotate to face the mother’s back (occipital anterior) as they descend through the birth canal. A clinical study found that roughly a third of babies completed this rotation during the active phase of the first stage, while almost another third rotated during the second stage itself, with the average rotation being about 63 degrees.5PubMed. The association among fetal head position, fetal head rotation and descent during the progress of labor A baby that doesn’t rotate fully can still be delivered vaginally, but the labor may be more difficult and the chance of needing instruments goes up.
Fetal heart rate monitoring is standard during this stage. The baby’s heart rate naturally dips during contractions and recovers between them, but certain patterns raise red flags. An elevated baseline heart rate or sustained slowing (bradycardia) during the second stage has been linked to newborn acidosis, which is a sign the baby is not getting enough oxygen.6PubMed. What changes in the fetal heart rate are associated with neonatal acidosis during the second stage of labor? When these patterns appear, the delivery team acts quickly, whether that means changing the mother’s position, providing supplemental oxygen, or moving to an operative or surgical delivery.
How Birthing Position Changes the Pelvis
The position you’re in while pushing matters more than many people realize, and the reason is mechanical. The pelvis is not a rigid frame; its joints flex under load, and different positions change the dimensions of the birth canal. MRI studies of pregnant women comparing the supine position to a kneeling squat found that shifting to the squat increased the midplane and pelvic outlet by up to 1 centimeter.7PubMed. Pelvic capacity in pregnant women, identified using magnetic resonance imaging A centimeter may not sound like much, but when the baby’s head is fitting through a tight space, every millimeter counts.
Computational simulations have explored this further. One model found that squatting increased the pelvic outlet in both the front-to-back and side-to-side dimensions, with the pregnant simulation showing larger gains than a non-pregnant one — about 6 millimeters front-to-back and 11 millimeters side-to-side. The peak increases occurred during the dynamic movement of squatting, not just in the resting squat posture, suggesting that active repositioning during labor can be helpful.8PubMed. The effects of squatting while pregnant on pelvic dimensions: A computational simulation to understand childbirth
Ultrasound measurements of the pubic joint tell a similar story: positions involving thigh flexion and the effect of gravity widened the pubic symphysis by about 1 millimeter compared to lying flat on the back.9Journal of Biomechanics. Measurement of pubic symphysis width in different birthing positions using ultrasound Despite this evidence, most hospital deliveries in Western countries still happen with the mother on her back or in a semi-reclined position, largely because of convention and the convenience of monitoring equipment and epidural use. The trade-off between pelvic space and clinical access is real, but it’s worth knowing that upright and squatting positions have measurable biomechanical advantages.
Protecting the Perineum During Delivery
As the baby’s head crowns, the tissue between the vaginal opening and the anus (the perineum) is under extreme stretch. Tearing is common, and providers use different techniques to reduce the risk. Manual perineal protection involves the provider placing a hand against the perineum to support it and control the speed at which the baby’s head emerges. There are specific named techniques for this — the Finnish and Viennese methods — with subtle differences in hand placement and pressure.10PubMed. Manual perineal protection: The know-how and the know-why
A randomized trial tested combinations of perineal protection and pushing style and found trade-offs. Hands-off care (no manual support) combined with uncoached pushing led to more first-degree tears, which are superficial and heal easily. But the hands-on approach with coached pushing led to more episiotomies (surgical cuts to widen the opening), with rates of about 46% versus 30%.11PubMed Central. Effects of manual perineal protection and pushing techniques used in the second stage of labor on perineal outcomes: a randomized controlled trial of combinations of strategies Neither approach eliminates all tearing, and the “right” technique often depends on the individual birth and the provider’s training. A survey of clinicians found that fewer than 6% could accurately describe the maneuvers they perform when protecting the perineum, which highlights a training gap rather than a lack of effort.10PubMed. Manual perineal protection: The know-how and the know-why
Pain Management and How It Affects Progress
Epidural analgesia is the most effective form of pain relief during labor and the most commonly used in hospital settings. It works by numbing sensation from roughly the waist down. The relief can be transformative, but epidurals do affect how labor unfolds. A Cochrane review noted that epidural analgesia prolongs the second stage and increases the rate of instrumental delivery.12PubMed Central. Position in the second stage of labour for women with epidural anaesthesia
A large study quantified this more precisely: epidural use added about 82 minutes to the upper end of second-stage duration for both first-time and experienced mothers and tripled the rate of prolonged second stage across the study population.13PubMed. The impact of epidural analgesia on the duration of the second stage of labor The reason is straightforward — reduced sensation means reduced ability to push effectively and diminished feedback from the pelvic floor muscles. This doesn’t mean epidurals lead to worse outcomes overall. For many people, the pain relief allows them to conserve energy and remain calm during a long labor. But it does mean the care team often allows more time before diagnosing a stalled second stage when an epidural is in place.
Non-pharmacological options include nitrous oxide, warm water immersion, movement and position changes, and continuous labor support from a doula or midwife. These have varying levels of evidence behind them but share the advantage of not affecting the ability to move and push. The choice is deeply personal and depends on pain tolerance, the intensity of contractions, and how the labor is progressing.
The Third Stage: Delivering the Placenta
After the baby is born, the uterus continues to contract. These contractions shear the placenta away from the uterine wall. The classic signs that the placenta has separated include the uterus becoming firmer and more rounded, a gush of blood, and the umbilical cord appearing to lengthen as the placenta descends.14American Journal of Obstetrics and Gynecology. Third stage of labor: evidence-based practice for prevention of adverse maternal and neonatal outcomes – Section: Physiology of the third stage of labor This stage typically takes 5 to 30 minutes.
Active management of the third stage, which includes giving oxytocin after the baby is born, gentle cord traction, and uterine massage, is now standard practice to reduce the risk of postpartum hemorrhage. Uterine atony, where the uterus fails to contract firmly after delivery, is the most common cause of excessive bleeding after birth. When it happens, the initial response involves emptying the bladder, massaging the uterus through the abdomen, removing any blood clots, and administering medications to stimulate contraction.15SASGOG. Postpartum Hemorrhage from Atony Unresponsive to First Line Uterotonics
Midwifery-led care sometimes takes a more hands-off approach during this stage. A scoping review of physiological third-stage management found that uninterrupted skin-to-skin contact, a calm and warm environment, and early breastfeeding all support the body’s natural oxytocin release, which helps the uterus contract on its own. The philosophy is that the same hormonal cascade that drove labor will finish the job if the mother isn’t distracted or distressed.16PubMed Central. Midwives’ Physiological Approach at the Third Stage of Labour: A Scoping Review Active management remains the safer default in hospital settings, particularly for higher-risk births, but the physiological approach is reasonable for low-risk, uncomplicated deliveries under skilled supervision.
The First Minutes After Birth
The moment a baby is born, a dramatic physiological shift begins. The lungs, which have been filled with fluid throughout pregnancy, must clear that fluid and begin breathing air. Research using imaging during newborn breathing has shown that the air-liquid boundary moves deeper into the lungs only during inhalation, with very little fluid pushed back up during exhalation. This means that the deep negative pressures generated by the baby’s first breaths are what drive fluid clearance — it’s an active, forceful process, which is why that first cry sounds so effortful.17PubMed. Imaging lung aeration and lung liquid clearance at birth
The timing of umbilical cord clamping has shifted considerably. For decades, the cord was clamped and cut within seconds of birth. Current evidence supports waiting at least one minute, and a growing body of research suggests that delaying up to three minutes or even longer is safe and beneficial. A study of more than 900 mother-infant pairs found that clamping beyond three minutes was not associated with negative outcomes for mother or baby, and the infants showed improved oxygen levels right after birth.18PubMed Central. Cord clamping beyond 3 minutes: Neonatal short‐term outcomes and maternal postpartum hemorrhage The main benefit is iron: the extra blood transfer from the placenta boosts the newborn’s iron stores, which can reduce anemia and support brain development in the months that follow.19PubMed. Delayed umbilical cord clamping – benefits and risks A clinical trial comparing one-, two-, and three-minute delays found that hemoglobin levels at 24 to 48 hours were highest in the three-minute group, with no increase in the need for phototherapy to treat jaundice.20PubMed Central. The Effect of Different Timings of Delayed Cord Clamping of Term Infants on Maternal and Newborn Outcomes in Normal Vaginal Deliveries
Immediate skin-to-skin contact between the mother and baby serves multiple purposes. The mother’s body helps regulate the newborn’s temperature, and the physical contact triggers oxytocin release in the mother, supporting uterine contraction and breastfeeding initiation. Research has also found that mothers who had early skin-to-skin contact reported lower depression scores at one week postpartum and showed a greater reduction in the stress hormone cortisol over the first month.21PubMed Central. Mother–Infant Skin-to-Skin Contact: Short‐ and Long-Term Effects for Mothers and Their Children Born Full-Term – Section: Effects of Skin-to-Skin Contact on Maternal Depressive Symptoms and Physiological Stress (Depression Scores and Salivary Cortisol Levels)
When Instruments Are Needed
Sometimes the second stage stalls or fetal monitoring suggests the baby needs to come out quickly, but the head is low enough that a vaginal delivery is still possible. In these cases, the provider may use forceps or a vacuum extractor. Both instruments help guide and pull the baby’s head through the birth canal.
The two tools carry different risk profiles. A Cochrane review found that the vacuum extractor caused significantly less maternal trauma than forceps and required less anesthesia. However, vacuum delivery was more likely to fail, meaning the provider had to switch instruments or move to a cesarean. And the vacuum was associated with a higher rate of cephalohematoma (a collection of blood under the scalp) and retinal hemorrhages in the newborn. Serious neonatal injury was uncommon with either instrument.22PubMed. Vacuum extraction versus forceps for assisted vaginal delivery
A more recent meta-analysis largely confirmed these patterns: forceps increased the risk of perineal tears and vaginal injuries, while vacuum extractors were linked to more infant scalp bleeding. The two instruments did not differ in their rate of failing to accomplish vaginal delivery.23PubMed Central. Efficacy of obstetrics forceps and vacuum extractor to assist during vaginal delivery: systematic review and meta-analysis The choice between them typically depends on the clinical situation and the provider’s experience. Forceps use has declined in many countries simply because fewer training programs teach the technique.
Handling Shoulder Dystocia
One of the most feared complications in vaginal delivery is shoulder dystocia, which happens when the baby’s head delivers but the anterior shoulder gets wedged behind the mother’s pubic bone. It requires immediate action because the baby’s oxygen supply through the cord is often compromised at this point.
The first maneuver typically attempted is the McRoberts maneuver: the mother’s thighs are sharply flexed against her abdomen, which changes the angle of the pelvis. Suprapubic pressure — a firm downward push on the mother’s lower abdomen just above the pubic bone — is often applied at the same time. But a systematic review found that McRoberts with or without suprapubic pressure resolves only about 26% of shoulder dystocia cases, which is lower than many providers assume.24Ibero-American Journal of Health Science Research. Effectiveness of combined obstetric maneuvers and instrumental assist techniques in the management of shoulder dystocia: a systematic review of maternal-fetal outcomes and associated complications
When that doesn’t work, the provider moves through additional maneuvers. Rotational techniques, where the provider reaches in and turns the baby’s shoulders, resolve roughly 62% of cases. Posterior arm delivery, where the provider sweeps the baby’s back arm across the chest and out, has the highest success rate at about 86%, and computational models show it places the least strain on the nerves running through the baby’s shoulder.25PubMed Central. Studying the effects of McRoberts and neonate-focused maneuvers on the neonatal brachial plexus during shoulder dystocia The sequence matters because each maneuver escalates in invasiveness, and providers are trained to move through them rapidly. Shoulder dystocia drills are a routine part of obstetric simulation training for exactly this reason — when it happens, the response has to be fast and practiced.
How Vaginal Birth Seeds the Newborn’s Microbiome
A less visible but increasingly studied aspect of vaginal delivery is its role in colonizing the newborn’s gut with microbes. As the baby passes through the birth canal, it picks up bacteria from the mother’s vaginal and intestinal flora. This initial “seeding” appears to influence the development of the infant’s immune system, and there are measurable differences in the gut microbiome profiles of babies born vaginally versus those born by cesarean section.26PubMed Central. The Maternal Infant Microbiome: Considerations for Labor and Birth
The details of which microbes transfer, and from where, are still being worked out. Research tracking specific bacterial strains found that the mother’s gut (not her vaginal flora) contributed more to the baby’s gut colonization by one month of age.27PubMed Central. The influence of maternal gut and vaginal microbiota on gastrointestinal colonization of neonates born vaginally and per caesarean section A longitudinal study of vaginal microbiota during pregnancy similarly found that the direct mother-to-child transfer of vaginal bacteria was modest, with the strongest sharing involving gut-dwelling bacterial groups rather than typically vaginal ones.28The ISME Journal. Ecological succession in the vaginal microbiota during pregnancy and birth This complicates the popular narrative that vaginal birth is primarily about vaginal bacteria seeding the baby’s gut. The real picture involves multiple routes of transfer — skin contact, breastfeeding, and the broader birth environment all play a role, and the maternal gut seems to be the bigger contributor.
Why Human Birth Is So Difficult in the First Place
If you’ve ever wondered why human birth is so much harder than it appears to be for other mammals, the answer involves an evolutionary compromise. Compared to most primates, humans have a remarkably tight fit between the baby’s head and the mother’s pelvis. The traditional explanation blamed bipedal walking: an upright gait required a narrower pelvis, which made birth harder. But research has identified another constraint. A wider birth canal means the pelvic floor muscles are suspended across a larger opening, which makes them less effective at supporting internal organs and maintaining continence.29PubMed Central. Biomechanical trade-offs in the pelvic floor constrain the evolution of the human birth canal In other words, the pelvis is a compromise between making birth easier and keeping everything else functional for the other decades of a person’s life. The tight fit isn’t a design flaw — it’s the least-bad option evolution arrived at, given competing demands on the same anatomy.