Human birth is a multi-stage process that begins when hormonal signals between mother and baby trigger labor contractions and ends when the newborn takes its first independent breaths. Most babies are born headfirst through the birth canal after several hours of labor, though about one in five births worldwide now happen by cesarean section. The process involves dramatic physical changes for both mother and baby, and understanding what actually happens at each step makes the whole event far less mysterious.
What Triggers Labor to Start
The onset of labor is driven by a conversation between the baby’s body and the mother’s. As the baby’s organs mature, the fetal adrenal glands ramp up production of a stress hormone (cortisol) that essentially signals readiness for life outside the womb. The mother’s body responds by increasing estrogen production and other preparatory changes.
In the weeks before labor, two key hormones reshape the cervix (the opening at the bottom of the uterus). Oxytocin and prostaglandins soften and thin it, a process called “ripening.” At the same time, the uterus builds more receptors for oxytocin, making it increasingly sensitive to the hormone’s effects. When the tipping point arrives, oxytocin triggers rhythmic uterine contractions that grow stronger and more regular, and labor officially begins.
The Three Stages of Labor
First Stage: Opening the Cervix
The longest part of labor is the first stage, when contractions gradually open the cervix from closed to 10 centimeters. This happens in two phases. The early (latent) phase involves slow dilation, typically from 0 to about 6 centimeters. For first-time mothers, this phase alone can last up to 20 hours. For women who have given birth before, it tends to cap around 14 hours.
Once the cervix reaches about 6 centimeters, active labor kicks in. Contractions become more intense and frequent, and dilation speeds up to roughly 1 to 2 centimeters per hour. The median duration of active labor is about 4 hours and 48 minutes for first-time mothers and around 2 hours and 25 minutes for those delivering a second baby.
Second Stage: Delivering the Baby
Once the cervix is fully dilated, the pushing stage begins. For first-time mothers without an epidural, this stage averages about 36 minutes, though the median is closer to an hour and a half when accounting for a wider range of experiences. With an epidural, it tends to run longer, averaging about an hour. For mothers who have delivered before, pushing is dramatically shorter, often under 20 minutes without an epidural.
Third Stage: Delivering the Placenta
After the baby is born, the placenta (the organ that supplied oxygen and nutrients throughout pregnancy) still needs to come out. This usually happens within 5 to 30 minutes. Three signs indicate the placenta is separating from the uterine wall: a gush of blood, the umbilical cord getting visibly longer, and the uterus firming into a round shape.
How the Baby Moves Through the Birth Canal
A baby doesn’t simply slide straight out. The birth canal is a tight, curved passage formed by the pelvic bones, and the baby navigates it through a series of specific movements. First, the baby’s head drops into the top of the pelvis, a step called engagement. This sometimes happens weeks before labor begins, sometimes not until contractions are well underway.
As contractions push the baby downward, the head tucks chin-to-chest, making the skull’s diameter as small as possible. The baby rotates to fit through the narrowest part of the pelvis. When the head reaches the pelvic floor, it extends upward and begins to emerge from the vaginal opening, the moment often called “crowning.” After the head is fully out, the baby rotates one more time so the shoulders can clear the pelvis. Then, typically with one final push, the shoulders, torso, and legs follow.
About 96 to 97 percent of babies settle into a head-down position before birth. Roughly 3 to 4 percent are in a breech position, with their feet or buttocks aimed downward. A small number lie sideways across the uterus. Breech and sideways positions often lead to a cesarean delivery because the head-down orientation is what allows the sequence of movements described above.
Cesarean Birth
When vaginal delivery isn’t safe or possible, a baby is delivered surgically through the abdomen. Globally, cesarean sections account for about 21 percent of all births. The most common reasons for a first-time cesarean include labor that stalls and stops progressing, concerning changes in the baby’s heart rate, the baby being in a breech or sideways position, and the baby being estimated as unusually large.
Some cesareans are planned in advance for medical reasons, such as certain infections, placenta positioning that blocks the cervix, or a previous cesarean scar. Others happen during labor when complications arise unexpectedly. In either case, the surgeon makes an incision through the skin, the layer of connective tissue over the abdominal muscles, and then through the uterine wall to reach the baby. The baby is lifted out, the umbilical cord is cut, and the placenta is removed. Recovery from a cesarean takes longer than a vaginal birth since it is major abdominal surgery.
The Baby’s First Moments Outside the Womb
The transition from womb to open air is one of the most dramatic physiological shifts a human body ever undergoes, and it happens in seconds. Inside the uterus, the baby’s lungs are filled with fluid and all oxygen comes through the umbilical cord from the placenta. The moment the baby is born, several things need to happen almost simultaneously.
The lungs must clear their fluid and fill with air for the first time. A substance called surfactant, which the baby’s lungs have been producing in preparation, keeps the tiny air sacs from collapsing with each breath. At the same time, the circulatory system undergoes a complete rerouting. In the womb, blood largely bypasses the lungs because they aren’t doing anything yet. With the first breaths, blood vessels in the lungs relax and open, allowing blood to flow through them to pick up oxygen. A small blood vessel that previously shunted blood away from the lungs gradually closes over the first hours and days of life.
Meanwhile, the removal of the placenta from the circulation causes a rise in blood pressure throughout the baby’s body, reinforcing the new pattern of blood flow. The fetal lung fluid clears into the bloodstream and lymphatic system over several hours. This entire cardiovascular and respiratory transformation is why the first cry is such a significant moment: it signals that the lungs are working and the new circulation is taking hold.
Cutting the Umbilical Cord
The umbilical cord, which connected baby to placenta throughout pregnancy, continues to pulse with blood for a short time after birth. The World Health Organization recommends waiting at least one minute after birth before clamping the cord, and many practitioners wait until the cord stops pulsing entirely. This delay allows additional blood to transfer from the placenta to the baby, which improves the infant’s iron stores for up to six months. Early clamping, done within the first 60 seconds, was once routine but has fallen out of favor as evidence of the benefits of waiting has accumulated.
Managing Pain During Birth
Labor contractions produce two types of pain. Early labor pain is visceral, a deep internal ache caused by the uterus contracting and the cervix stretching. As labor progresses, somatic pain joins in, a sharper sensation from pressure on the pelvic floor and birth canal.
An epidural, the most effective form of labor pain relief, works by delivering anesthetic near the spinal nerves that carry both types of pain signals. In studies comparing epidurals to injected pain medications, over 92 percent of women receiving epidurals reported effective pain relief throughout labor, compared to only 10 percent of those receiving traditional injections. Epidurals also avoid the nausea and newborn respiratory effects associated with injected opioid medications. The tradeoff is that epidurals can lengthen the pushing stage and limit mobility during labor.
Other options include nitrous oxide (inhaled gas), warm water immersion, and various non-medication techniques like positioning changes and counterpressure. The approach varies widely depending on the birth setting, personal preference, and how labor unfolds.