Pelvimetry is a measurement that is made of the diameters of the mother’s pelvis, both the upper and lower strait, in relation to the diameter of the fetus’s head to find out if there is a possible disproportion that makes vaginal delivery difficult, and should have a caesarean section.
Measurement can be done by clinical examination, X-ray, CT (Computed Tomography) examination, or MRI (Magnetic Resonance Imaging).
However, it is a practice that has fallen into disuse. According to current management, “due to the potential danger of exposure to ionizing radiation, radiopelvimetry has been moved away from the scene to make way for dynamic pelvimetry , as it is currently called active management of labor, with the fetus now assuming function of the “dynamic pelvimeter”.
What is cephalopelvic disproportion?
The term cephalopelvic disproportion (CPD) or fetopelvic disproportion (PFD) is used to describe a disparity between the dimensions of the fetal head and the maternal pelvis, resulting in slowing or stopping of cervical dilation and descent of the fetal head despite the presence of adequate uterine contractions, which precludes vaginal delivery.
That is, the delivery does not prosper because the baby’s head is too large and cannot pass through the birth canal due to the narrowness of the mother’s hip.
However, many experts point out that true cephalopelvic disproportions practically do not exist , and that the delivery does not prosper is most of the time due to a bad position of the fetus or other factors that interfere with vaginal delivery.
Why is pelvimetry discouraged?
A Cochrane review (Pattinson) published in March 2017 based on five trials with 1,159 pregnant women found that women who received X-ray pelvimetry were more likely to have a caesarean section . Therefore, he concludes:
There is insufficient evidence to support the use of X-ray pelvimetry to decide the mode of delivery in women with fetuses in cephalic presentation.
Based on scientific evidence, the WHO in its Recommendations for care during childbirth, for a positive childbirth experience also points out:
Routine clinical pelvimetry at admission for delivery in healthy pregnant women is not recommended.
The Clinical Practice Guide for Pregnancy and Postpartum Care of the Ministry of Health does not recommend it either:
It is suggested not to perform a pelvimetry in order to assess the need for caesarean section in women with a full-term cephalic baby.
Dynamic Fonts
Since pelvimetry is not recommended to decide whether or not vaginal delivery is possible, the current position is to observe how labor progresses.
As explained by Dr. Jorge Carvajal in his Manual of Obstetrics and Gynecology:
The concept of cephalo-pelvic or feto-pelvic proportionality leads to the obstetric aphorism that the best pelvimetry is trial of labor . That is to say, that the compatibility of a birth canal to allow the passage of a certain fetus is not necessarily demonstrated by means of pelvimetry, but it may be necessary to assess, in the given case, if the fetus can pass through that birth canal. .
It is necessary to be very cautious in the trial of labor, since an overzealous effort to assess feto-pelvic compatibility can lead to obstetric disaster. The labor trial consists of observing the dilation of the cervix and the descent of the presentation, determined by uterine contractions in a period not exceeding 2 – 4 hours, with uterine dynamics of sufficient frequency and intensity, strictly monitored and with strict control of the fetal condition.
