Childbirth begins with the onset of labor, which consists of contractions that lead to progressive cervical dilation and effacement, eventually resulting in the birth of the infant and expulsion of the placenta. The process of normal childbirth depends on a high degree of anatomical and physiological compatibility between the mother and child. The birth canal is the passage consisting of the mother's bony pelvis and soft tissues through which a fetus passes during vaginal delivery. Fetal orientation during childbirth is described in terms of lie, presenting part, position, attitude of the presenting part, and station. The clinical status of the mother and fetus should be consistently monitored during labor and delivery. While vaginal delivery is typically preferred, cesarean delivery may be indicated under certain circumstances. Complications of normal vaginal delivery include perineal lacerations, hemorrhage, nerve injuries, and coccydynia.
See “Abnormal labor and delivery” for intrapartum complications and their management.
Orientation in utero
- Definition: relation of the fetal long axis to the long axis of the maternal uterus
- Longitudinal lie: fetus is in the same axis (most common)
- Transverse lie: fetus is at a 90° angle
- Oblique lie: fetus is at a 45° angle
- Definition: part of the fetus that overlies the maternal pelvic inlet
- Cephalic presentation: head (most common)
Breech presentation: buttocks or feet
- Frank breech: flexed hips and extended knees (buttocks presenting)
- Complete breech: thighs and legs flexed (cannonball position)
- Single Footling breech: hip of one leg is flexed and the knee of the other is extended (one foot presenting)
- Double Footling breech: both thighs and legs are extended (feet presenting)
- Compound presentation: ≥ 1 anatomical presenting part (e.g., cephalic or breech presentation with presentation of an extremity)
- Shoulder presentation: shoulder presentations combined with a transverse or oblique lie
- Definition: relationship and orientation (i.e., fetal occiput pointing towards maternal left or right) of the presenting fetal part to the maternal pelvis
Occiput anterior position: Fetal occiput points towards maternal symphysis pubis; fetus faces downwards.
- Left occiput anterior (LOA): Fetal back faces the maternal left, anterior fontanelle faces the maternal right, sagittal suture lies in the right ; (most common position).
- Right occiput anterior (ROA): Fetal back faces the maternal right, anterior fontanelle faces the maternal left, sagittal suture lies in the left .
- Occiput posterior position: Fetal occiput points towards the maternal sacral promontory with face to pubis symphysis; the fetus faces upward
- Sacrum in breech presentation
- Mentum (chin) in extended cephalic (face) presentation
- Occiput anterior position: Fetal occiput points towards maternal symphysis pubis; fetus faces downwards.
Fetal attitude 
- Definition: degree of extension/flexion of the fetal head during cephalic presentation
- Vertex presentation (maximally flexed); most common attitude
- Brow presentation (partially extended)
- Face presentation (maximally extended)
- Forehead presentation (partially flexed; military attitude): Spontaneous vaginal delivery is possible .
Station (Obstetrics) 
- Definition: measurement (in cm) of the presenting part above and below the maternal ischial spine
- Engagement (Obstetrics)
- Definition: parallelism between the pelvic plane and the plane of the fetal head
- In asynclitism, the sagittal suture is in the transverse diameter of the pelvic inlet and not between the symphysis pubis and sacral promontory.
Anterior asynclitism (Naegele obliquity)
- The sagittal suture is positioned towards the sacral promontory
- Spontaneous vaginal delivery possible
- Posterior asynclitism (Litzmann obliquity)
- Anterior asynclitism (Naegele obliquity)
Obstetric contractions (uterine muscle contractions) 
|Overview of obstetric contractions |
Uterine contractions during pregnancy
|Alvarez-waves|| || |
|Braxton Hicks contractions (false labor)|| || |
|Prelabor|| || |
|Labor||Stage 1: cervical dilation and effacement|| || |
|Stage 2: fetal expulsion|| || |
|Stage 3: placental expulsion or afterbirth|| || |
|Afterpains|| || |
False labor only requires reassurance.
Rupture of membranes (ROM)
- Definition: the rupture of the amniotic sac followed by the release of amniotic fluid
- Spontaneous rupture of membranes: ROM that usually occurs at the onset of labor and is unprovoked by health practitioners
- Artificial rupture of membranes (amniotomy): A procedure in which the amniotic sac is ruptured in order to release amniotic fluid.
- Delayed rupture of membranes: ROM that occurs during fetal expulsion, after cervical dilation and effacement
- Abnormal rupture of membranes
- Clinical features: sudden “gush” of pale yellow or clear fluid from the vagina (may also be a constant leaking sensation)
- Consider sterile speculum examination if the diagnosis is uncertain.
- Suggestive findings include pooling, positive or , and .
Stages of labor 
|Overview of the stages of labor|
|Nulliparous patients||Multiparous patients|
|First stage of labor||Latent phase of labor|| || |
|Active phase of labor|| || |
|Second stage of labor|| || || |
|Third stage of labor|| |
|Fourth stage of labor|| || || |
Management of labor by stage
First stage of labor
- Analgesia upon request
- Fetal heart rate monitoring
- Determine fetal position via abdominal (see ) and pelvic (palpation of fetal sutures/fontanelles) examination.
- Regular assessment of cervical dilation and descent of the fetal head
- Amniotomy may be performed during the active phase if the fetal head is well applied (lying against the cervix).
- In case of heavier bleeding but normal maternal vital signs and fetal heart tracing (e.g., increased bloody show), delivery should proceed as planned with frequent observation.
Second stage of labor
- Warm compresses and perineal massage
- Helping the mother to find comfortable and safe positions
- Guide the delivery of the fetus through vaginal canal (See “Mechanics of childbirth” for expected fetal movements).
- Delay cord clamping for ∼ 1 minute; alternatively, milk the cord (to enhance blood transfusion to the newborn). 
Third stage of labor
- Fundal massage: massaging of the uterine fundus to induce its contraction and stop bleeding
- (reduces the risk of )
- Examine the placenta to confirm completeness (regular surface with complete cotyledons), which should also consist of the umbilical cord, complete amniotic membranes, and three blood vessels (one vein, two arteries).
- Repair any .
- Fourth stage of labor: Monitoring to rule out preeclampsia or
Normal mechanics of childbirth 
Adaptation to the different forms of the pelvic region requires a great deal of rotation.
- Engagement, descent, and increased flexion (occur simultaneously)
- Internal rotation: The fetal head rotates by 90° (two 45° steps) in the midpelvis, from a transverse to anterior-posterior position.
- Extension: The fetal head, lying behind the symphysis pubis bone and the pelvic floor, acts upwards and forwards.
- Restitution: The fetal head rotates 45° in the opposite direction as it passes through the pelvic outlet.
- External rotation: The anterior shoulder rotates 45° anteriorly as it meets the maternal pelvic floor. This action is transmitted to the head which also rotates 45°, placing the head in its original transverse position.
- Expulsion: Delivery of the head, anterior shoulder followed by the posterior shoulder, and the body
Electronic fetal heart rate monitoring 
- Description: widely used diagnostic tool during 3rd trimester and labor to detect signs of fetal distress
- Determination of the (FHR), presence of acceleration or deceleration by Doppler ultrasound, recording beats per minute (bpm) in the upper curve (cardiogram)
- During birth, the FHR may be monitored internally via an electrode that is attached to the fetal head (fetal scalp electrode monitoring).
- Mechanoelectrical measurement of uterine contractions via a pressure transducer, recording in the lower curve in kPa (tocodynagraph)
Fetal heart rate 
- In CTG, the FHR is designated as the baseline or basal heart rate and is normally 110–160 bpm.
- Methods to assess FHR: NST) and (CST) (; are performed during the third trimester of pregnancy to measure FHR reactivity to fetal movements and FHR reactivity in response to uterine contractions respectively. See nonstress test and contraction stress test in “ ” for details.
Fetal heart rate (FHR) tracing
|Fetal heart rate tracing categories|
|Category I FHR tracing||Category II FHR tracing||Category III FHR tracing|
Fetal heart rate variability 
|Overview of fetal heart rate variability|
|Moderate variability|| || |
|Absent variability|| || |
|Minimal variability|| |
|Marked variability|| |
|Sinusoidal variability|| |
|Pseudosinosoidal variability|| || |
Acceleration (CTG) 
- Description: a normal temporal increase in the FHR from the baseline by > 15 bpm for more than 15 seconds but less than 10 minutes if the gestational age is > 32 weeks, or by > 10 bpm for more than 10 seconds if the gestational age is < 32 weeks
Decelerations (CTG) 
- Description: a temporary decline in the FHR of > 15 bpm for a maximum duration of 3 minutes
|Overview of types of fetal deceleration|
| || |
|Variable deceleration|| || |
|Prolonged deceleration|| |
|MNEMONIC for etiology of fetal HR alterations: VEAL CHOP|
|Variable decelerations||→ Cord compression/prolapse|
|Early decelerations||→ Head compression|
|Late decelerations||→ Placental insufficiency/Problem|
Nonreassuring fetal status
- Characteristic changes in the fetal heart rate (FHR) in response to fetal hypoxia and metabolic acidosis
- A nonreassuring tracing requires and/or immediate delivery (cesarean or, if imminent, vaginal delivery).
- Reassuring fetal status
See “” for details.
Complications of delivery
- Definition: tear of the perineal area due to significant or rapid stretching forces during labor and delivery
- Epidemiology: most common obstetric injury of the pelvic floor
- Risk factors 
Classification ; 
- First degree: cutaneous to subcutaneous tissue tear (skin, fourchette, posterior vaginal wall) with no involvement of the perineal muscles
- Second degree: first-degree lacerations plus laceration of the perineal muscles without involvement of the anal sphincter
- Third degree: second-degree lacerations plus involvement of the external anal sphincter (may lead to fecal incontinence due to sphincter involvement)
- Fourth degree: third-degree lacerations plus lacerations of the anterior wall of the anal canal or rectum
- Clinical features: symptoms of a missed perineal laceration (occult perineal laceration) may manifest immediately or up to months after delivery ; 
- First and second degree: Minor tears (e.g., superficial, hemostatic lacerations) are left to the clinician’s discretion to determine if suturing is required. 
- Third and fourth degree
- Complications 
- Prevention: application of warm compress to perineum during delivery
Acute nerve injury can occur during childbirth due to compression, transection, traction, or vascular injury to the nerve.
|Obstetric nerve injuries|
|Nerve||Clinical features||Risk factors|
|Pudendal nerve injury|
- Etiology: injury to the coccyx during childbirth as a result of internal and external pressure on the coccyx during labor and delivery
- Clinical features
- Diagnosis: clinical
- Prognosis: resolves spontaneously in the majority of patients (> 90%) 
Postpartum retroperitoneal hematoma
- Epidemiology: rare (∼ 1:1000) 
- Etiology: injury to branches of the internal iliac artery (most commonly, uterine artery)
- Clinical features
- Diagnostics: imaging (e.g., sonography, CT)
Planned home birth
- In the US, approx. 1% of births per year are home births.
- 75% of these home births are planned.
- There is insufficient evidence to determine what makes a good candidate for a home birth.
- Home births can be considered in individuals with no contraindications.
- Patients who would like to plan a home birth should be advised about the benefits and risks of home birth compared to hospital delivery in order to make an informed decision.
- Advantages compared to hospital delivery
- Disadvantages compared to hospital delivery
- Absolute contraindications
- Relative contraindications