Normal labour Flashcards
Name some important terms
- Labor (parturition) – expulsion of uterine products later than >24 weeks of gestation. Process
includes uterine contractions, cervical changes, fetal delivery and ends with placental delivery.
- Pre-term labor – labor occurring before <37 weeks.
- Prolonged labor – labor lasting more >20 and >14 hours (nulliparous and multiparous
respectively) - Miscarriage – spontaneous loss of a fetus before <24 weeks of gestation
- Childbirth – labor and delivery
Stages of labor
1st stage
- Early (latent) phase
- Active phase
- Transition phase
2nd stage
- Passive (pelvic) phase
- Active phase
3rd stage
First stage
regular painful contractions and cervical changes (until reaches full dilatation).
- Early (latent) phase
- Active phase
- Transition phase
Early (latent) phase 1st stage
i. Cervical effacement (thinning) and dilation up to 3cm.
ii. Contractions every 5-30 minutes for 30-45 seconds.
iii. Lasts between 6-8 (multipara and nullipara respectively)
Active phase 1st stage
i. Cervical dilation from 3cm to 8cm at a rate of 1cm/hour
ii. Contractions every 3-5 minutes for 45-60 seconds.
iii. Lasts between 3-5 hours (multipara and nullipara respectively)
Transition phase 1st stage
i. Cervical dilation from 8cm to full dilation (10cm) at a rate of 1cm/hour
ii. Contraction every 0.5-2 minutes lasting 60-90 seconds.
iii. Lasting between 0.5-2 hours (multipara and nullipara respectively)
Second stage
from full dilatation to delivery of fetus
Passive (pelvic) phase
Active phase
Second stage
-Passive (pelvic) phase
Passive (pelvic) phase
i. Head descent down the pelvis due to cervical dilatation and effacement
(no maternal efforts at this point)
Second stage
-Active phase
Active phase
i. Fetus is pushed by maternal effort and uterine contractions
ii. Terminology related to this stage:
* Crowning – appearance of the fetal head in the vaginal opening
* Vernix - white substance (sebum, lipids, shed skin) found coating the
fetus for birth facilitating birth and for thermal protection
Third stage
from delivery of the fetus to delivery of the placenta and membranes. Signs of
placental separation:
a. Small stream of bright blood
b. Lengthening of umbilical cord
c. Elevation of the fundus of the uterus
The Brandt-Andrew maneuver
is controlled cord traction
(CCT).
Check the integrity of the whole placenta to rule out remaining placental tissue. Retained placenta – if the
placenta is not detached for more than 30 minutes.
Can cause hemorrhage and infection. Manage using oxytocin and CCT. In severe and rare cases
(e.g. placenta accreta) curettage (scraping) is needed to remove the remaining tissue.
Onset of labor
Clinical signs
a. Regular, painful contractions that increase in frequency, duration and intensity that
produce progressive cervical dilatation and effacement.
b. Blood and mucus plug passing from the cervix called “bloody show” (not enough on its
own)
c. Rupture of (fetal) membranes (ROM) – also called amniorrhexis.
i. Premature (pre-labor) rupture of membranes (PROM) – when the time between
ROM and onset of labor is greater than 4 hours.
Before <37 weeks called
preterm premature rupture of membranes (PPROM)
ii. “En caul birth” – is when the baby comes out still inside an intact amniotic sac.
Onset of labor
Key points
a. Diagnosis of labor is important to avoid unnecessary interventions such as artificial
rupture of membranes (ARM) or use of oxytocin infusion.
b. Difficult to be certain about the onset because contractions may be irregular with no
cervical changes – false labor
c. Based on observed cervical changes and uterine contraction along with descent of the
head.
Onset of labor
Mechanism
Uterine contractions
Cervical changes
Uterine contractions
Onset of labor
placental development leads to increase in syncytiotrophoblasts
→ increase in CRH (corticotropin releasing hormone), hCG, oxytocin, relaxin (and more
hormones) in the mother and fetal plasma → CRH acts on several targets:
i. On the placenta to increase estrogen and decrease progesterone
ii. On fetal adrenal glands to produce DHEA which is a precursor of estrogen
iii. Stimulation of prostaglandins by membranes
All of these changes lead to increased contractions of uterine myocytes by acting on the Ca influx of ion channels
Cervical changes
Onset of labor
– contains myocytes and fibroblasts → towards term becomes soft and
stretchy due to leucocytes infiltration → degrade collagen and increase hyaluronic acid
→ water is attracted to hyaluronic acid → ripening of the cervix.
Uterine activity in labor
power, passages and passenger
Power
i. Infrequent, low-intensity contraction throughout pregnancy are replaced by the
activity of contractions that show an increase in frequency, duration and
strength as full-term approaches.
ii. Identification of these contractions by palpitation or tocography and
intrauterine pressure by a measuring catheter (normal resting tone is around
10-20mmHg)
iii. Establishment of labor is likely when 2 contractions last >20 seconds in a period
of 10 minutes.
iv. Retraction - progressive contractions lead to effacement and dilatation of cervix
due to shortening of myometrial fiber in the upper segment and stretching and
thinning of lower segment.
v. As uterus and round ligaments contract the longitudinal axis are pulled towards
the abdominal wall and the realignment if the axis is what promotes the descent
of the presenting part.
vi. Obstructed labor – an abnormal junction between the upper and lower
segments may become visible at the level of the umbilicus called retraction ring
(Bandl’s ring)
Passages
Structure of bony pelvis (described in earlier chapters)
viii. Size and shape of the pelvis varies and effects the outcome of labor.
ix. Softening of sacroiliac ligaments and pubic symphysis allow expansion of pelvic
cavity.
Passenger
Fetal size, lie and position (described in earlier chapters)
Mechanism of labor
- Descent – occurs throughout labor. Engagement of head occurs before onset of labor in the
majority of primigravid but not multipara. Provides measure of the progress of labor. - Flexion – head flexes towards the chest which reduces the diameter of presentation. Begins
from deflexed occipito-frontal diameter to suboccipitobregmatic diameter which is fully flexed. - Internal rotation – head rotates when it reaches pelvic floor and the occiput is facing anteriorly
towards the pubic symphysis in most cases but also face-to-pubis delivery may occur. - Extension – head extends until it is delivered. The occiput comes in contact with the inferior
rami of the pubis. - Restitution – after delivery the head, it rotates back to its normal relationship with the
shoulders. - External rotation – shoulders reach pelvic floor and rotate antero-posteriorly.
- Delivery of shoulders – final expulsion of trunk occurs after shoulders are delivered.
