Normal labour Dr Hiba Ahmed Suhail M.B. Ch. B./F.I.B.O.G. College of medicine University of Mosul

Objectives of this lecture To know stages of labour To know symptoms of onset of labour To know mechanism of normal labour

Labour is the process by which the products of conception are expelled from the uterus begin naturally about term. . The last few hours of human pregnancy are characterized by uterine contractions that cause cervical dilatation and cause the fetus to descend through the birth canal That is, uterine contractions that bring about progressive cervical dilatation ,effacement and delivery of the fetus . It divided in to False labour and true labour the latter divided into the three stages :

1. The first stage, is the stage of cervical effacement and dilatation begins when widely spaced uterine contractions of sufficient frequency, intensity, and duration cause cervical dilitation and thinning (effacement). this labour stage ends when the cervix is fully dilated—about 10 cm—to allow passage of the fetal head 2. The second stage stage of fetal expulsion begins when cervical dilatation is complete, and ends with delivery of fetus –fetuses . 3. The third stage stage of placental separation and expulsion. begins immediately after delivery of the fetus and ends with the delivery of the placenta and membranes

Symptoms & signs of the onset of labour Painful uterine contractions The show Rupture of membranes Shortening&dilatation of cervix

The uterine contractions The uterus contracts irregular&painless throughout pregnancy[Braxton hicks contractions] labour is recognized by regular & painful contraction during which uterus is felt harden with increase in duration ,intensity & frequency. At end of first stage it may come every two to three minutes & last 45 seconds to one minute.

The interval between contractions diminishes gradually from about 10 minutes at the onset of the first stage of labour to one minute or less in the second stage . Periods of relaxation between contractions, are essential for fetal welIbeing and contractions compromise uteroplacental blood flow sufficiently to cause fetal hypoxemia. In active-phase labour the duration of each contraction ranges from 30 to 60 seconds.

During active labour, the uterine divisions IN TO UPPER AND LOWER UTERINE SEGMENT The upper segment is firm during contractions it contracts, retracts (does not relax to its original length after contractions. it becomes relatively fixed shorter in length maintaining the advantage gained in the expulsion of the fetus). The lower segment is softer, distended, and more passive.. In response to contractions OF UPPER SEGMENT , the softened lower uterine segment and cervix dilate form a greatly expanded, thinned-out tube through which the fetus can pass. As a result of the lower segment thinning and concomitant upper segment thickening a boundary between the two is—the physiological retraction ring. When the thinning of the lower uterine segment is extreme, as in obstructed labour, the ring is prominent and forms a pathological retraction ring is also known as the Bandl ring,

Cervical Changes During First-Stage Labour As the result of contraction forces, two fundamental changes effacement and dilatation take place in cervix. 1-Dilatation When labour begins the contraction& retraction of upper segment stretches lthe lower segment & upper part of cervix so that the internal os is pulled and open , the cervix is dilated from above downwards becoming shorter until no projection into vagina is felt Factors leading to cervical dilatation in labour Uterine contraction As uterine contractions cause pressure on the membranes , the hydrostatic action of the amniotic sac in turn dilates the cervical canal like a wedge. In the absence of intact membranes, the pressure of the presenting part against the cervix and lower uterine segment is similarly effective.

Cervical dilatation is divided into Latent phase It starts at the point at which the mother perceives regular contractions. The latent phase ends at 3 cm of dilatation. beyond which active labour started the cervix become fully effaced , it is of variable duration in nullipara 3-8 hrs but shorter in multipara Prolonged Latent Phase exceeding 20 hours in the nullipara and 14 hours in the multipara

Active phase From the 3-4 cm dilatation to 10 cm it is variable in length lasting 3-6 hrs but shorter in multipara, the rate of cervical dilatation usually 1cm -1hr in nullipara and 2cm –hr in multipara

2-Cervical effacement is “taking up” of the cervix It is manifest clinically by shortening of the cervical canal from a length of about 2.5 - 3.5 cm to a circular orifice with almost paper - thin edges. Effacement causes expulsion of the mucous plug (show ).

The show This is mucous discharge from the cervix mixed with little blood as a result of taking up of the internal os & separation of membranes.

Rupture of the membranes The membranes may rupture at any time during labour&usually occurs towards the end of first stage of labour. Early rupture of membranes is more likely to occur if the presenting part not engaged or there is malpresentation.

First Stage Of Labour The uterine contraction&dilatation of internal os cause separation of chorion from decidua closest to it thus a small back of membranes is formed into the internal os,the head then comes down separates liquor amnii which is above it from that in the back called respectively the hind&forewaters.When membranes ruptured the fetal axis pressure comes into play ;the upper pole of fetus is pressed on by the fundus of the uterus

While the lower pole is pressed down onto the lower segment&cervix. Normal first stage should not exceed 12 hours in a primegravida&8 hours in multipara. The character of pain is the same as spasmodic dysmenorrhoea caused by ischaemia of uterine muscles from compression of blood vessels in the wall of the uterus

Second Stage of Labour This stage begins when cervical dilatation is complete and ends with fetal delivery. The presenting part is pushed down onto the pelvic floor It is highly variable in nillipara 2 hrs with out epidural analgesia and 3hrs with it ,while in multi para 1hrs increased to 2hrs with epidural analgesia Divided in to two phases the passive and the active phase passive phase time between the fully cervical dilatation but no urge to push Active phase is the stage of forceful contraction to deliver fetus

the most important force in fetal expulsion is that force which overcome pelvic floor resistance : Maternal intra-abdominal pressure. Contraction of the abdominal muscles . forced respiratory floor resistance has to be overcome by uterine contractions efforts . uterine contraction .

With each contraction the presenting part is forced down to pelvic floor, during intervals between contraction at first slipped back ,after this with contraction&expulsive effort the head slowly moves down in a forward direction,when the widest diameter of the head distends the vulva it is said to be crowned.Then the head passed through vulva followed by the body in next contraction

Third Stage of Labour: Delivery of Placenta and Membranes This stage begins immediately after delivery of the fetus and involves the separation and expulsion of the placenta and membranes. As the neonate is born, the uterus spontaneously contracts the uterine fundus now lies just below the level of the umbilicus. This sudden diminution in uterine size is inevitably accompanied by a decrease in the area of the placental implantation site the placenta ordinarily separates within minutes after delivery. placenta is expelled from vagina followed by membranes &any retroplacental blood clot lasting 30-60-minutes.

THE MECHANISM OF LABOUR

■ Mechanisms of Labour This is referred to series of changes in position & attitude which the fetus undergoes during its passage through the birth canal The positional changes in the presenting part (fetal head )required to navigate the pelvic canal constitute called the mechanisms of labour the vertex enters the pelvis with the sagittal suture lying in the transverse pelvic diameter. The fetus enters the pelvis in the left occiput transverse (LOT) position or in occipto anterior (OA) Cardinal movements of labour are engagement, descent, flexion, internal rotation, extension, restitution external rotation, and expulsion (delivery of shoulder and body ) During labour, these movements not only are sequential but also show great overlap.

. The following terms are used to describe the position of fetus in relation to the uterus & maternal pelvis: 1-Fetal Lie The relation of the long axis of the fetus to the uterus,this may be longitudinal,oblique or transverse.

2-Prsentation Is that part of the fetus that occupies the lower uterine segment ( in or over the pelvic brim in relation to the cervix).If the head occupies the lower segment the presentation is cephalic,if is flexed on the spine the vertex presents. If the head is fully extended this face presentation, & if is partly extended cause brow prsentation. If the breech occupies lower segment termed Podalic presentation.If the fetus lies obliquely caused shoulder presentation.

3-Fetal Position Position refers to the relationship of a certain portion of the fetal presenting part to the right or left side of the birth canal(maternal pelvis ). Accordingly, with each presentation there may be two positions—right or left. The fetal occiput, chin (mentum), and sacrum are the determining points in vertex, face, and breech presentations, respectively Because the presenting part may be in either the left or right position, there are left and right occipital, left and right mental, and left and right sacral presentations, abbreviated as LO and RO, LM and RM, and LS and RS, respectively

4-Attitude Refers to the relation of different parts of the fetus to one another.Normally the head ‘back&limbsof fetus are flexed,in some abnormal presentation head or limbs may be extended.

The mechanism of labour in vertex presentation; -Engagement -Descent -Flexion -Internal rotation -Extention -Restitution -External rotation -Shoulder rotation -Delivery of fetal body

Engagement I n which the biparietal diameter(—the greatest transverse diameter in an occiput presentation)—passes through the pelvic inlet The fetal head may engage during the last few weeks of pregnancy (NULLIPARA )or not untill after labour occur (MULTIPARA ). In many multiparous and some nulliparous women, the fetal head is freely movable above the pelvic inlet at onset of labour. the head is referred to as “floating.” The fetal head usually enters the pelvic inlet either transversely or obliquely. THE NUMBER OF FIFTH PALPABLE OF THE HEAD IS DETERMINE THE ENGAGMENT IF 2-5PALPABLE ABDOMINALLY THE HEAD ENGAGED

Descent Station describes descent of the fetal biparietal diameter in relation to a line drawn between maternal ischial spines. This movement is the first requisite for birth of then ewborn. Active descent usually takes place after dilatation has observed during cervical dilatation phase. During the first stage &first phase of the second stage of labour descent of the fetus is secondary to uterine action . In the second phase of the second stage of labour descent of fetus is helped by voluntary use of abdominal musculature

Flexion As soon as the descending head meets resistance from the cervix ,wall of the pelvis, or pelvic floor, then flexion of the head results.so, the chin is brought into more intimate contact with the fetal thorax, and the shorter suboccipitobregmatic diameter is presented . This is probably as a passive movement in part due to the surrounding structures.

Internal Rotation In a well flexed head , the occiput will be the leading point (denominator )and when reach the sloping gutter of the levator ani muscle the head will forced to rotate anteriorly the occiput rotate forward from the LOA or LOT position to lie under subpubic arch,so that the saggital suture lies on the antero posterior diameter of the pelvis Turning of the head that the occiput gradually moves toward the symphysis pubis anteriorly

Extension After internal rotation, the sharply flexed head reaches the introitis and undergoes extension.. The well flexed head now extends with the occiput escaping from underneath the the symphysis pubis&starting to distend the perineum ,this is known as crowning of the head When the head presses upon the pelvic floor two forces come into play. first force, exerted by the uterus, acts more posteriorly, and the second, by the resistant pelvic floor and the symphysis, acts more anteriorly. thereby causing head extension. This brings the base of the occiput into direct contact with the inferior margin of the symphysis pubis With progressive distension of the perineum and birth canal opening, an increasingly larger portion of the occiput gradually appears. The head is born as the occiput, bregma, forehead, nose, mouth, and finally the chin pass successively over the anterior margin of the perineum

Restitution When the head is delivering,the occiput is directly anterior .As soon as it escapes from the perineum ,the head aligns itself with the shoulders,which have entered the pelvis in the oblique position.The slight rotetion of the occiput through one-eighth of a circle is called restitution

External rotation In order to be delivered,the shoulders have to rotate into direct anterior-posterior plane. When this occurs,the occiput rotate through a further one-eighth of a circle to the transverse position.

Expulsion (delivery of the shoulder and rest of the body ) Immediately after external rotation, the anterior shoulder appears under the symphysis pubis and delivered first , and the perineum soon becomes distended by the posterior shoulder and delivered subsequently . After delivery of the shoulders, the rest of the body easily and quickly passes