Childbirth (also called labour, birth, partus or parturition) is the culmination of a human pregnancy with the emergence of a newborn infant/s from the mother's uterus.

The process of human childbirth is categorized in 3 stages of labour. In the first stage, the uterus begins rhythmic contractions which steadily increase in strength and frequency, gradually widening and thinning the cervix. During the second stage, the infant passes from the uterus, through the cervix and birth canal. In the third stage, the placenta pulls from the uterine wall and is expelled through the birth canal.

The natural birth

First stage: contractions

A typical childbirth will begin with the onset of contractions of the uterus. The frequency and duration of these contractions varies with the individual. The onset of labour may be sudden or gradual, and is defined as regular uterine activity in the presence of cervical dilatation.

During a contraction the long muscles of the uterus contract, starting at the top of the uterus and working their way down to the bottom. At the end of the contraction, the muscles relax to a state shorter than at the beginning of the contraction. This draws the cervix up over the baby's head. Each contraction dilates the cervix until it becomes completely dilated, often referred to as 10+ cm (4") in diameter.

A gradual onset with slow cervical change towards 3 cm (just over 1 inch) dilation is referred to as the "latent phase". A woman is said to be in "active labour" when contractions have become regular in frequency (3-4 in 10 minutes) and about 60 seconds in duration. The cervix must shorten (efface) before it can dilate; for first time mothers this can take a substantial period of time and can often be a very tiring and disheartening time. However, it is also a very positive time, as once the cervix is effaced dilatation can occur and the downward journey of the fetus can commence. The now powerful contractions are accompanied by cervical effacement and dilation greater than 3 cm. The labour may begin with a rupture of the amniotic sac, the paired amnion and chorion ("breaking of the water"). The contractions will accelerate in frequency and strengthen. In the "transition phase" from 8 cm–10 cm (3 or 4 inches) of dilation, the contractions often come every two minutes and are typically lasting 70–90 seconds. Transition is often regarded as the most challenging and intense for the mother. It is also the shortest phase.

During this stage, the expectant mother typically goes through several emotional phases. At first, the mother may be excited and nervous. Then, as the contractions become stronger, demanding more energy from the mother, mothers generally become more serious and focused. However, as the cervix finishes its dilation, some mothers experience confusion or bouts of self-doubt or giving up. It is important during this time for the birth partners to stay positive and supportive of the mother; to actively encourage if this is what she wishes and to provide nutrition and hydration in order to keep her energy reserves up.

The duration of labour varies widely, but averages some 13 hours for women giving birth to their first child ("primiparae") and 8 hours for women who have already given birth.

If there is a significant medical risk to continuing the pregnancy, induction may be necessary. As this carries some risk, it is only done if the child or the mother are in danger from prolonged pregnancy. Forty-two weeks' gestation without spontaneous labour is often said to be an indication for induction although evidence does not show improved outcomes when labour is induced for post-term pregnancies. Inducing labour increases the risk of cesarean section and uterine rupture in mothers that have had a previous cesarean section.

Second stage: delivery

In the second stage of labour, the baby is expelled from the womb through the vagina by both the uterine contractions and by the additional maternal efforts of "bearing down," which many women describe as similar in sensation to straining to expel a large bowel movement. The imminence of this stage can be evaluated by the Malinas score.

The baby is most commonly born head-first. In some cases the baby is "breech" meaning either the feet or buttocks are descending first. Babies in the breech position can be helped to be born vaginally by a midwife, although caesarean births are becoming more common for breech presentation.

There are several types of breech presentations, but the most common is where the baby's buttocks are born first and the legs are folded onto the baby's body with the knees bent and feet near the buttocks (full or breech). Others include frank breech, much like full breech but the babies legs are extended toward his ears, and footling or incomplete breech, in which one or both legs are extended and the foot or feet are the presenting part. Another rare presentation is a transverse lie. This is where the baby is sideways in the womb and a hand or elbow has entered the birth canal first. While babies who present transverse will often move to a different position, this is not always the case and a cesarean birth then becomes necessary.

The length of the second stage varies and may be affected by whether a woman has given birth before, the position she is in and mobility. The length of the second stage should be guided by the condition of the fetus and health of the mother. Problems may be encountered at this stage due to reasons such as maternal exhaustion, the front of the baby's head facing forwards instead of backwards (posterior baby), or extremely rarely, because the baby's head does not fit properly into the mother's pelvis (Cephalo-Pelvic Disproportion (CPD)). True CPD is typically seen in women with rickets and bone deforming illnesses or injuries, as well as arbitrary time limits placed on second stage by caregivers or medical facilities.

Immediately after birth, the child undergoes extensive physiological modifications as it acclimatizes to independent breathing. Several cardiovascular structures start regressing soon after birth, such as the ductus arteriosus and the foramen ovale. In some cultures, the father cuts the umbilical cord and the infant is given a lukewarm bath to remove blood and some of the vernix on its skin before being handed back to its parents.

The practice of leaving the umbilical cord to detach naturally is known as a Lotus Birth.

The medical condition of the child is assessed with the Apgar score, based on five parameters: heart rate, respiration, muscle tone, skin color, and response to stimuli. Apgar scores are typically assessed at both 1 and 5 minutes after birth.

Third stage: placenta

In this stage, the uterus expels the placenta (afterbirth). Breastfeeding the baby will help to cause this. The mother normally loses less than 500 mL (2 cups) of blood. It is important to note that the placenta is to never be pulled from the mother by an untrained person; this could cause it to tear and not be expelled in whole. It is essential that the placenta be examined to ensure that it was expelled whole. Remaining parts can cause postpartum bleeding or infection.

The alternative to natural delivery of the placenta is what is called Active Management - this involves administration of a prophylactic oxytocic before delivery of the placenta, and usually early cord clamping and cutting, and controlled cord traction of the umbilical cord.

A Cochrane database study suggests strongly that blood loss and the risk of postpartum bleeding will be reduced in women offered active management of the third stage of labour. However, the group treated with active third phase management, there was an increased risk of unpleasant side effects (eg nausea and vomiting), and hypertension. The authors suggest that this is due to the use of ergometrine as a component of the oxytocic. No advantages or disadvantages were apparent for the baby.

After the birth

Medical professionals typically recommend breastfeeding of the first milk, colostrum, to reduce postpartum bleeding/hemorrhage in the mother, and to pass immunities and other benefits to the baby.

Parents usually bestow the infant its given names soon after birth.

Often people visit and bring a gift for the baby.

Many cultures feature initiation rites for newborns, such as naming ceremonies, baptism, and others.

Mothers are often allowed a period where they are relieved of their normal duties to recover from childbirth. The length of this period varies. In China it is 30 days and is referred to as "doing the month". In other countries taking time off from work to care for a newborn is called "maternity leave" and varies from a few days to several months.