Transcript Normal Labour - Sun Yat

Normal Labor
XIE MEIQING
29/09/2006
Labor means the process of the
birth,which is finished by the effective
coordination of uterine contractions and
pushing-down efforts, the lower segment
stretching, effacement and dilatation of
cervix. It is a process.
Labor begins from the onset of
uterine contraction and terminate with the
expulsion of the products of pregnancy.
There is another term—delivery,which
describes the phenominum of the actual
expulsion of the products: fetus and
placenta.But it has the same meaning as
labor in Chinese.
Several definitions
abortion:< 28 week pregnancy
labor:≥28 week pregnancy
preterm labor :28 → < 37
week pregnancy
term labor:≥37→ < 42
week pregnancy
postterm labor :≥ 42
week pregnancy
Labor can be normal or abnormal.It is
influenced by three essential factors，We
can named the three factors in “ The Three
P”
the three P
1. the powers ---- forces
2. the passage ---- birth canal
3. the passenger ---fetus(baby) and placenta
The power
1 uterine contraction : is involuntary,
rhythm, symmetry and polarity, called retraction
2 abdominal wall contraction
and lelator ani contraction :
called bearing—down efforts,is voluntary，which
help to deliver the baby after the cervix os fully
dilated.They create from the contraction of
abdominal wall muscle and diaphrum muscle and
lebator ani muscle.
a. rhythm: the uterine contractions are
rhythmical\ periodic and progressive.which called
“Pains”. In the very beginning of labor, each
contraction last about 30 seconds, and the interval
between two contractions is 5 to 10 minutes, as the
labor progresses, each contraction may last longer
and longer, and the intervals may become shorter
and shorter and be stronger and stronger. And when
the cervix fully dilates,the uterine contraction may
be as longer as 60 seconds,and the intervals may be 1
to 2 minutes.
b. Symmetry and polarity: the contractions
create from two poles of uterus, then go to the
fundus and upper part of the uterus, then go down to
the lower segment , the forces of the upper segment
are more powerful than that of lower segment of
uterus.
c.
Retraction: after each contraction
the length of each myometrium muscle
of the uterus can not return to the former
length, it becomes shorter and shorter.
The uterine capacity is progressively
reduced so the pressure inside uterus
becomes stronger and stronger.
The passage
1 Bony passage
2 Soft passage
Bony passage : also called the true
pelvis , it composed of four bones: sacrum,
coccyx and two innominate bones, each
innominate bone is formed by the fusion of
the ilium, ischium and pubis.
Because the shape and size of the true
pelvis are crucial in labor so each
diameter of the pelvis is very
important.If each diameter fits the baby
the labor will be finished easily, if not
abnormal labor will occur. For easy
understanding, We can imagine four planes
of the true pelvis:
the inlet(brim)
widest plane
mid plane
outlet
a. The plane of the inlet( the brim): the brim is
bounded anteriorly by the pubis, laterally by the
iliopectineal lines,posteriorly by the sacrum
promontory, four diameters are mentioned here:
the antero- posterior diameter------from the superior
border of the pubic symphysis to the middle of the
sacral promontory, measures 11cm..
the transverse diameter------- between two
illiopectineal,measures 13cm.
The oblique diameters------ two oblique diameters,
left oblique diameters from left sacro-iliac joint to
the right iliopubic tubercle. Right one from right
sacrro-iliac joint to the left iliopubic tubercle,
mesrers 12.75cm.
b.
The mid plane of pelvis:this is the smallest
and most important plane.two diameters will be
mentioned here:
The antero-posterior diameter------from the apex of
the pubic arch through the middle of the transverse
diameter of ischium spines to the sacrum,measures
11.5cm..
The transverse diameter------ between two ischial
spines meassures 10cm. This is the most important
diameter when baby head descends through the mid
plane of the pelvis. abnormal labour may occur when
it is shorter than normal.
c.
The plane of outlet: the lowerest boundary of
the bony passage and abnormal labor may after
occur here. Four diameters mentioned:
The anter-posterior diameter------from the inferior
border of symphysis to the sacro-coccygeal
joint,measures 11.5cm.
The transvwese diameter------also called the intertuberous diameters,measures 9cm,which between the
two ischial tuberosities, is the important diameter
when the baby’s head going through the outlet of the
pelvis.
The anterior sagittal diameter------from the arch of
the symphysis to the middle of the transverse
diameter,measures 6cm.
The posterior sagittal diameter------ from the sacrococcygeal joint to the middle of the transverse
diameter measures 8.5cm.
Soft passage :lower segment
cervix
vagina
pelvic floor
1. Formation of the lower segment of the uterus:
it comes from the isthmus uteri, which is 1cm in
non-pregnant uterus, it can be stretches much longer
and become thinner during pregnancy and labor due
to uterine contractions.
2. Changes of the cervix
(1)Effacement : The shortening of the cervical
canal is called effacement of the cervix; Before
labour, the length of the canal is about 2cm but
gradually shortened during labour and acts as a
functional part of the lower uterine segment.
(2) Dilatation of the cervical os : The cervical os
dilates gradually during labour. When the dilatation
has reached 10 cm in diameter, it is said "complete"
or "full". This is achieved by the contraction of the
uterus and the ligaments ,and also by the hydrostatic
action of the forewater bag.
3. Changes of the pelvic floor,vagina and
perineum
The stretching of the fibres of the levator ani and
the thinning of the central portion of the perineum
transforms to almost transparent membranous
structure.
The Passenger(the foetus)
1. Foetal size
Large foetus (macrosomia) (weight>or=4kg)may
cause dystocia due to cephalo-pelvic disproportion.
a. Biparietal diameter---BPD,most important, mesures 9.3cm
in mature infant.
b.Suboccipitobregmatic diameter--measures 9.5cm, fit the
mid pelvis when the baby head going through
c.Occipito frontal diameter--mesures 11.3cm, the engagement
diameter.
d.Occipitomental diameter—mesures 13.3cm, the largest
diameter of the head.
2.Foetal position
Abnormal position or presentation may cause
dystocia.
3. Foetal malformation
Malformation of the foetus such as hydrocephalus ,
monster, conjoined twin may cause dystocia.