physiological changes during 1st stage of labor

7/23/2019 Physiological Changes During 1st Stage of Labor

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Physiological changes during first stage of labor

The first stage is chiefly concern with the preparation of

the birth canal so as to facilitate expulsion of the fetus in

the 2nd stage. During first stage of labor, following

physiological changes are occurs.

1. Uterine action

I. Contraction and retraction of uterine muscles


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Uterine contractionare involuntary, they are controlled

by the nervous system and endocrine influence.

Normally the uterus begins to contract effectively 280

days after the !". #ontraction consists of regular,

painful with hardening of uterus. The patient experiences

pain, which is situated more on the hypogastric region,

often radiating to the thighs. "robable causes of pain aremyometrial hypoxia during contractions, stretching of

the peritoneum over the fundus, stretching of the cervix

during dilatation and compression of the nerve ganglion.

$t earlier the contractions are often wee% and may beimperceptible to the mother but it becomes more

powerful at last.


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The feature of uterine contraction:

Frequency: &t is the interval of each contraction. &n the early

stage of labor, the contractions come at intervals of ten to

fifteen minutes. The intervals gradually shorten with

advancement of labor until in the second stage, when it comes

every two or three minutes.

Duration: &t is length of each contraction. &n the first stage, the

contractions last for about '0 seconds initially but gradually

increase in duration with the progress of labor. Thus in second

stage, the contractions last longer then in the first stage.


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Retraction is a phenomenon of the uterus in labor in which the muscle

fibers are permanently shorted. #ontraction is a temporary reduction in

length of the fibers, which attain their full length during relaxation. &n

contrast, retraction results in permanent shortening and the fibers are

shorted once and for all. etraction is a specially a property of upper

uterine segment. &t ma%es upper segment of uterus gradually shorter and

thic%er in progressive nature after each contraction and cavity diminishes

which %eeps place with the gradual descent of the presenting part.

The effects of retraction which is essential in normal labor are-

ormation of upper and lower uterine segment.

Dilatation and effacement of up of the cervix.

educe the surface area of the uterus favoring separation of placenta.

!aintain the advancement of presenting part and help in expulsion of

fetus.


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II. Fundal dominance:

/terine contraction that is strongest at the top of the

uterus and wea%est in the lower uterine segment. ach

uterine contraction starts in the fundus near one of the

cornua and spreads across and downwards. Thecontraction lasts longest in the fundus where it is also

most intense, but the pea% is reached simultaneously over

the whole uterus and the contraction fades from all parts

together. This pattern permits the cervix to dilate and the

strongly contracting fundus to expel the fetus.


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II. Cer$ical dilatation:

Dilatation of cervix is the process of enlargement of the

os uteri from a tightly closed aperture to an openinglarge enough to permit passage of the fetal head.

Dilatation is measured in centimeters and full dilatation

at e;uates to about +0cm.

Dilatation occurs as a result of uterine action and the

counter pressure applied by the bag of membranes and

the presenting part. $ well )flexed fetal head closely

applied to the cervix favors efficient dilatation. "ressureapplied evenly to the cervix causes the uterine fundus to

respond by contraction.


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III. Presentation of (ho":

&t is the bloodstain mucoid discharged seen a few hours

before, or with in a few hours after labor has started.

During pregnancy a woman


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II. +eneral fluid !ressure

7hile the membranes remain intact, the pressure of

uterine contractions is exerted on the fluid and as fluid is

not compressible, the pressure is e;uali4ed through out the

uterus and over the fetal body and is %nown as general

fluid pressure. 7hen the membrane ruptures and ;uantity

of fluid emerges, the placenta is compressed between the

uterine wall and the fetus during contractions and theoxygen supply to the fetus is thereby diminished and there

is ris% of fetal hypoxia during uterine contraction.


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I. Fetal a%is !ressure

During each contraction the uterus rears forward

and the force of the fundal contraction is

transmitted to the upper pole of the uterus, down

the long axis of the fetus and is applied by the

presenting part to the cervix. This is %nown as fetal

axis pressure and becomes much more significant

after rupture of the membranes and during the

second stage of labor.

physiological changes during 1st stage of labor

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