Physiology of labor

Labor process was divided in to 3 stages. The first stage star when the uterus has enough

frequency, intensity, and duration to produce progressive landfall and dilatation of cervix. The

first stage is over when the cervix has opened completely (around 10 cm) so that enable the head

of the fetus through. The second stage star when the dilatation of the cervix was complete, and

over when the fetus was born. The third stage star as soon as the fetus outward, and over by

outward of the placenta and omniotic membrane.

Diagnosis of stage and phase of labour

Symptoms and Signs Stage Phase

• Cervix not dilated False labour/Not in

labour

• Cervix dilated less than 4 cm First Latent

• Cervix dilated 4–9 cm

• Rate of dilatation typically 1 cm per

hour or more

• Fetal descent begins

First Active

• Cervix fully dilated (10 cm)

• Fetal descent continues

• No urge to push

SecondEarly (non-

expulsive)

• Cervix fully dilated (10 cm)

• Presenting part of fetus reaches

pelvic floor

• Woman has the urge to push

Second Late(expulsive)

 

The third stage of labour begins with delivery of the baby and ends with expulsion of placenta.

Uterus activity differentiation

During labor, uterus’s form changes into two different parts. Upper segment contracts actively

become more thick during labor. The lower segment is passive compare with the upper segment,

and this part develop become delivery was which has very thin wall. Miometrium in the upper

segment doesn’t relax until reach the length before after contraction, but become constant in the

shorter length. But the strain still same like before contraction. Upper part of uterus contract

downward although when the volume decreases, so that miometrium strain still constant. The

last effect is strain the loose, by defend good condition that was gotten by fetus expulsion and

maintain uterus muscle stay adhere into uterus. As retraction consequences, all the next

contraction star in the place that left by contraction before, so that upper cavity of the uterus

becomes smaller in each contraction. Because shorten of muscle fiber continue in every

contraction, upper active segment of the uterus become thicker as long as first and second stage

and become very thick exact after fetus delivery.

Obliteration and Dilatation of cervix

Obliteration is shortening of cervix canal from length about 2 cm become just around orifice

with the edge near thin like a paper. When uterus contraction produces pressure to amniotic

membrane, hydrostatic pressure of amniotic membrane will dilate cervix canal.

Delivery of the fetus

Active contraction of the uterus of increasing strength, frequency, and duration cause passive

movement of the fetus down the birth canal. At the beginning of labour, the lie, presentation and

engagement of the fetus are assessed. As the labour progresses, the neck becomes fully flexed so

that the suboccipitobregmatic diameter is presenting.

Descent occurs when the head is engaged, followed by internal rotation to bring the occiput into

the anterior posterior when it reaches the pelvic floor. In the second stage of labour, the occiput

descends below the symphysis pubis and the movement of extension pushes the head forwards

and delivers the occiput. Increasing extension round the pubic bone delivers the face.

The fetal head normally engages in the maternal pelvis in an occiput transverse position, with the

fetal occiput transverse in the maternal pelvis

Occiput transverse positions        

With descent, the fetal head rotates so that the fetal occiput is anterior in the maternal pelvis

(occiput anterior positions. Failure of an occiput transverse position to rotate to an occiput

anterior position should be managed as an occiput posterior position.

 

Occiput anterior positions 

   

The head of the baby come in to through pelvic rim can be divided into 3 situations.

Sinklitismus, if the axis direction of fetus’s head is straight upright with pelvic rim area.

Asinklitismus, if the axis direction of fetus’s head is oblique to pelvic rim area. Anterior

asinklitismus according to Naegele is when the axis direction of fetus’s head make sharp angle to

front by pelvic rim. Posterior asinklitismus according to Litzman ia when the condition is opposit

Delivery of the head brings the shoulder into pelvic cavity, with the head oblique to the line of

the shoulders. Restitution occurs: the head rotates to the natural position in relation the shoulders.

Finally, In the process of external rotation continuing descent and rotation of the shoulders

brings their widest diameter into the anteroposterior diameter of the pelvic outlet. This enables

the anterior shoulder to pass under the pubis. Lateral flexion of the fetus delivers the posterior

shoulder and the rest of the body follows.

As soon as the baby born, amplitude of his was same high, just the frequency decrease. Because

of this his, uterus will decrease in size so that placenta sticking to uterus wall will be free. The

sticking of placenta from uterus wall can be started from 1) middle (central according to

Schultze); 2) edge (marginal according to Mathew-Duncan); 3) combination 1 and 2. The most

one is according to Schultze. Generally the third stage happened about 6 till 15 minutes. The

high of uterus after the third stage about 2 fingers below umbilicus.

By: Tri Mardiyana

Source :

Ilmu kebidanan (Kusnarman Keman)

Crash Course: Obstetrics and Gynaecology