Cephalic position of the fetus is the longitudinal position of the fetus with the head facing the entrance to the pelvis. Depending on the adjacent part of the fetal head, the occipital, anterior, frontal and facial location are distinguished. The definition of fetal presentation in obstetrics is important for predicting childbirth. The presentation of the fetus is found out during the examination with the help of special obstetric techniques and ultrasound. Cephalic position is the most common and desirable for independent childbirth. However, in some cases (with frontal presentation, posterior appearance of facial presentation, etc.), surgical delivery or the imposition of obstetric forceps may be indicated.
General information
Cephalic position of the fetus is characterized by the child’s head turning to the inner throat of the cervix. With the cephalic position of the fetus, the largest part of the child’s body is the head, which first moves along the birth canal, allowing the shoulders, trunk and legs to be born quickly and without much difficulty after it. Up to 28-30 weeks of pregnancy, the presenting part of the fetus may change, however, closer to the time of delivery (by 32-35 weeks), in most women, the fetus takes a cephalic position. In obstetrics, there are head, pelvic and transverse presentation of the fetus. Among them, cephalic position occurs most often (in 90% of cases), and the absolute majority of natural childbirth occurs precisely with this arrangement of the fetus.
Variants of cephalic position
With the cephalic position, several options for the location of the head are possible: occipital, anterior, frontal and facial. Among them, obstetrics and gynecology considers flexion occipital presentation to be the most optimal. The leading point of advancement along the birth canal is the small fontanel.
With the occipital variant of the cephalic position during the passage through the birth canal, the neck of the child turns out to be bent in such a way that at birth the first to appear is the back of the head facing forward. This is how 90-95% of all births occur. However, with cephalic position of the fetus, there are variants of extensor insertion of the head that differ from each other.
- I degree of extension of the head – anterolateral (anteroleminal) presentation. In the case of anterior presentation of the fetus, a large fontanel becomes the leading point during the period of expulsion. Anterolateral presentation of the fetus does not exclude the possibility of independent childbirth, however, the probability of birth trauma of the child and mother is higher than with the occipital variant. Childbirth is characterized by a prolonged course, therefore, with such a presentation, it is necessary to prevent fetal hypoxia.
- II degree of extension of the head – frontal presentation. Frontal cephalic presentation is also characterized by the entry into the pelvis of the fetal head by its maximum size. The wired point through the birth canal is the forehead, lowered below other parts of the head. In this case, natural childbirth is impossible, and therefore operative delivery is indicated.
- III degree of extension of the head – facial presentation. The extreme degree of extension of the head is the facial version of the cephalic position of the fetus. In this case, the leading point is the chin; the head exits the birth canal backwards with the back of the head. In this case, the possibility of independent childbirth is not excluded, provided that the pelvis of a woman or a small fetus is sufficiently large. Nevertheless, facial presentation in most cases is considered as an indication for cesarean section.
Extensor variants of cephalic position account for about 1% of all cases of longitudinal positions. The reasons for various non-standard positions and presentation of the fetus can be the presence of a narrow pelvis in a pregnant woman; abnormalities of the structure of the uterus, uterine fibroids that limit the space available to the child; placenta previa, polyhydramnios; flabby abdominal wall; heredity and other factors.
Diagnosis
The presentation of the fetus is determined by an obstetrician-gynecologist, starting from the 28th week of pregnancy using methods of external obstetric examination. To do this, the doctor places the open palm of his right hand over the symphysis and covers the adjacent part of the fetus. With the cephalic position of the fetus above the entrance to the pelvis, the head is determined, which is palpated as a dense rounded part. The cephalic position of the fetus is characterized by balloting (mobility) of the head in the amniotic fluid.
The data of the external examination are clarified during the vaginal gynecological examination. The heartbeat during the cephalic position of the fetus is heard under the navel of the woman. With the help of obstetric ultrasound, the position, position, presentation, position of the fetus and its type are specified.
Tactics of childbirth with cephalic position
Correct and prognostically favorable in obstetrics are considered to be childbirth occurring with an anterior view of the occipital cephalic position of the fetus (the occiput is facing anteriorly), which contributes to the creation of optimal relationships between the size and shape of the head, as well as the pelvis of the woman in labor.
In this case, when entering the pelvis, the fetal head bends, the chin turns out to be close to the chest. When moving through the birth canal, the small fontanel is the leading wire point. Bending the head slightly reduces the adjacent part of the fetus, so the head passes through the pelvis with its smaller size. Simultaneously with moving forward, the head makes an internal turn, as a result of which the back of the head turns out to be facing the pubic joint (anteriorly), and the face – to the sacrum (posteriorly). When the head is eruption, its extension is performed, then there is an internal turn of the shoulders and an external turn of the head in such a way that the baby’s face is turned to the mother’s hip. Following the birth of the shoulder girdle, the trunk and legs of the child appear without difficulty.
In the case of the course of labor in the posterior form of the head occipital presentation of the fetus, the occiput unfolds to the sacral cavity, i.e. posteriorly. The progressive advancement of the head with posterior-occipital cephalic position of the fetus is delayed, and therefore there is a possibility of developing secondary weakness of labor activity or birth asphyxia. Such deliveries are conducted expectantly; in the case of weak labor, stimulation is performed, with the development of asphyxia, obstetric forceps are applied.
The mechanism of childbirth with anterior cephalic position of the fetus in the main points coincides with the previous version. The wired point with such a presentation of the head is a large fontanel. The tactics of childbirth are of a wait-and-see nature; operative delivery is undertaken in case of a threat to the health of the mother or fetus.
With frontal cephalic position of the fetus, independent childbirth is extremely rare, it takes a long time with a prolonged period of exile. With independent childbirth, the prognosis is more often unfavorable: complications in the form of deep perineal ruptures, uterine ruptures, the formation of vaginal-vesicular fistulas, asphyxia and fetal death are not uncommon. If a frontal cephalic position is suspected or determined, a fetal rotation may be performed even before the insertion of the head. In the absence of the possibility of rotation, a caesarean section is indicated. With a complicated course of independent labor, a craniotomy is performed.
The conditions for a successful independent delivery with a facial cephalic position of the fetus are the normal size of the pelvis of the woman in labor, active labor activity, a small fetus, an anterior view of the facial presentation (the chin facing forward). Childbirth is conducted expectantly, careful monitoring of the dynamics of labor and the condition of the woman in labor, fetal heartbeat is carried out using cardiotocography, phonocardiography of the fetus. With a posterior view of the facial presentation, when the chin is turned posteriorly, a caesarean section is required; with a dead fetus, a fruit-destroying operation is performed.
Prevention
Pregnancy management in women at risk is associated with an abnormal course of labor. Such women should be hospitalized in a maternity hospital in advance to determine the optimal delivery tactics. With timely diagnosis of the incorrect position or presentation of the fetus, the cesarean section operation is most favorable for the mother and child.
