Fig. 4.1
(a) POP-Q points after Bump RC et al. [13]. (b) All patients in the nonpregnant group had a POP-Q stage of 0 or 1 (c) 47.6 % of the pregnant subjects had POP-Q stage 2 (p < .001). Point Ba (most distal position of the remaining upper anterior vaginal wall) and point Bp (most distal position of the remaining upper posterior vaginal wall) are significantly different
Furthermore, as pregnancy progresses the prolapse stages become more pronounced [15]. O’Boyle et al. demonstrated that there is a significant difference between the first and third trimester for all anterior and posterior vaginal points in the POP-Q as well as for the total vaginal length and the genital hiatus, not so for the apical suspension (point C/D), though.
Apart from using the Pelvic Organ Prolapse Quantification (POP-Q) system, pelvic organ support can be assessed using relevant quality of life questionnaires. One prospective study looked at pelvic floor symptoms in the course of pregnancy and POP-Q stages [16]. Quality of life was assessed with the electronic Personal Assessment Questionnaire-Pelvic Floor (ePAQ-PF). Bother with voiding difficulties and stress urinary incontinence increased during pregnancy. Constipation (p = 0.02) and evacuation subdomains improved significantly (p = 0.009) between the week 20 to week 36 of pregnancy. Fecal incontinence was not present in either trimester of pregnancy. In the sexual domain, the only subdomain that worsened significantly (p = 0.03) was “sex and vaginal symptoms” in the course of pregnancy. None of the pelvic floor symptoms impacted the overall quality of life. Objective parameters like genital hiatus and perineal body length showed significantly higher values in the third trimester compared to the second trimester. In this study, other POP-Q points for the anterior or posterior vaginal wall as well as the cervix location did not differ between the second and third trimester.
Other Findings
More data on developmental histomorphological changes in pelvic floor muscles, ligaments, connective tissue and nerve supply in pregnant women would be beneficial. Biomechanical studies on biological tissues like the pelvic ligaments and vaginal tissue have been performed [17] in postmenopausal women with prolapse.
In 29 female cadaveric specimens a correlation between subjective evaluation and objective strength of ligaments was found [18]: the ileopectineal ligament was significantly stronger than the sacrospinous and the arcus tendineus fascia pelvis. But as the influence of hormones during pregnancy is remarkable, these results can not be translated to pregnant women.
At present there is a lack of data about pregnancy associated pelvic floor damage by contrast with an abundance of studies on intrapartum injuries and age-related changes contributing to the development of prolapse.
Outcome Assessment of Pelvic Floor Muscle Training (PFMT)
Pelvic floor muscle changes during pregnancy can be assessed through palpation of the pelvic floor muscles or vaginally or rectally placed pressure sensors. These measurements also allow to assess therapy outcome of pelvic floor muscle training, the only recommended therapy during pregnancy to prevent further pelvic floor disorders. The concept of pelvic floor muscle training (PFMT) in pregnancy to prevent urinary incontinence has been supported by recent studies, which showed that PFMT can prevent from urinary incontinence (UI) both during and in the immediate postpartum period [19–21]. In a recent Cochrane review, there was evidence of a statistically significant effect of PFMT during pregnancy on prevention of incontinence at 3 and up to 6 months after delivery [22]. Long-term follow up of participants up to 8 years after their initial randomization showed that 35.4 % of women in the PFMT group versus 38.8 % of women in the control group reported urinary incontinence [21]. Mørkved et al. reported in a conference abstract non-significant differences in the long-term outcome, whereby after 6 years the incontinence rate was higher in the group that had PFMT (urinary incontinence in 23 % of PFMT and 17 % of control women), however the sexual satisfaction was higher in women that had PFMT during pregnancy [19, 22].
According to the Cochrane Database of Systematic Reviews [22], PFMT is especially recommended for women with incontinence prior to pregnancy, women with a bladder neck hypermobility in early pregnancy, or postpartum for women that delivered a large baby and/or had a forceps delivery.
A recent study that assessed the outcome of meticulous PFMT with surface electromyography and quality of life questionnaire in pregnant and postpartum women, demonstrated a successful outcome in all three groups. The pelvic floor muscle contractility increased after the training program (p = 0.0001) in the early pregnancy group, in the postpartum group that delivered vaginally with an episiotomy and the postpartum group after an elective caesarean section. Decreases in the scores of both ICIQ-UI SF (P = 0.009) and ICIQ-OAB (P = 0.0003) were also observed after training in all three groups. One point that has to be investigated further is to evaluate if such effects are maintained after stopping training [23].
Imaging Techniques During Pregnancy
Imaging techniques are beneficial to measure changes of the pelvic floor in a non-invasive, reproducible way. Ultrasound and magnetic resonance imaging, as safe and volume based techniques, allow visualisation of structures and function in real time.
Ultrasound
2D Transperineal Ultrasound and Endovaginal 3D Ultrasound
2D ultrasound has a resolution of up to 0.1 mm. The probe held on the perineum in a sagittal position, allows to depict similarly the symphysis, urethra, bladder neck, bladder, vagina and rectum (Fig. 4.2).
Fig. 4.2
Midsagittal B-mode view of the pelvic floor of a pregnant women in the third trimester. Arrow = rectum, triangle = fetal head, asterisk = vagina, dot = urethra (empty bladder), rectangle = symphysis
Since the introduction of ultrasound in the early 1960s, safety issues were discussed. Ultrasound, physically longitudinal waves, have an influence on biological systems. Physical effects are thermal effects, as energy gets transformed to warmth/heat and second there is a pressure application that can lead to tissue deformation (cavitation). In the B-mode the power is very low (<10 mW/cm2) and the duration of pulses are short (<1 μs). Temperature rises are not measurable for the B-mode ultrasound (US).
3D/4D Transperineal Ultrasound
3D-pelvic floor US generates a volume data set, which can be cut in sequential, orthogonal planes to study structures that are not accessible in the 2D-sonography. The advantage of applying 3D US is that reference planes orthogonal to non-linear structures like the vagina or anal canal can be set time-independently after the examination. Those examinations are also safe, as the applied power is far below the level of biological significance (<100 mW/cm2). Worldwide there are no reports of harmful effects to the fetus through B-mode US which is also the basis for 3D/4D US.
Magnetic Resonance Imaging
Pelvic floor MRI usually performed in a 1.5 or 3 T superconducting magnet, uses proton density T2-weighted scans, 2-D fast-spin proton density with an echo time of 15 ms and a repetition time of 4000 ms, performed at 5-mm intervals in the axial, sagittal and coronal planes in the supine position. Common settings use a slice thickness of 4 mm with a gap of 1 mm. Like ultrasound, magnetic resonance has no harmful effects to the mother and child (Fig. 4.3). Disadvantages are the higher costs, the narrow space of the MR tube and the noise of the machine.
Fig. 4.3
Coronal MRI slides of a women in the second trimester; thickness of slices is 5 mm. The vertical course of the levator ani as thin muscle layer (white arrow head), the bulk of the obturator internus muscle (asterisk) and the internal cervical os in the third picture (arrow) are visible
Pelvic Floor Muscle Anatomy and Function
The female pelvic floor is a complex fibro-muscular-ligamentous unit involved in multiple functions that go beyond the sole support of pelvic organs. Pelvic floor dysfunction globally affects micturition, defecation and sexual activity. Evolutionary modifications like upright walking and the need to deliver fetuses with larger head diameters made the fascial and muscle support of the pelvic floor vulnerable, therefore predisposing women to pelvic organ prolapse and incontinence. The female pelvic floor further undergoes a number of adaptive changes related to pregnancy and endocrine changes.
Animal Studies
Women are not the only upright species that develop pelvic floor disorders during life. Animal studies in primates simulate pregnancy and parturition-related changes. Primates like squirrel monkeys are also known to develop prolapse during their life-time. To study the effects of pregnancy and parturition on the pelvic floor, MRIs of seven female squirrel monkeys were studied prior to pregnancy, 3 days, and 4 months postpartum [24]. No testing was performed during pregnancy to avoid harming the fetus. The bladder neck and cervix position were measured dynamically with abdominal squeezing. The pelvic floor muscles are not completely alike in humans, one difference is a prominent coccygeus muscle. The volume of the coccygeus muscle was greater shortly after parturition than before pregnancy or after recovery. The bladder neck position in the relaxed state and with abdominal pressure descended (p < 0.04) after delivery and descended further (p < 0.001) after recovery. The same happened to the position of the cervix. It seems that parturition-related bladder neck descent in squirrel monkeys is permanent.
Levator Ani Changes in Humans
The appearance of the levator ani (LA) muscle in pregnancy was assessed in 3D-MRI in 84 post-term nulliparas (at 41 weeks of gestation) [25]. This study found a lower levator ani volume in post-term pregnant women of a mean volume of 13.5 ± 3.7 cm3 than in nulligravida, where LA volumes vary between 32.3 and 46.6 cm3 [26–29]. In this investigation on post-term pregnancies the LA muscles appear to be thinned. However, it has to be pointed out that this difference might be partly due to different acquisition techniques.
A 3D ultrasound study [30], aimed to predict delivery outcomes in relation to the levator hiatus area, assessed the LA of 61 nulliparous women between 36 and 40 weeks of pregnancy. The mean hiatal area at rest was 11.81 cm2, at contraction 9.59 cm2, and at Valsalva 16.03 cm2. A correlation between levator dimensions and delivery mode could not be demonstrated. However, an inverse correlation was demonstrated between the area of the hiatus, particularly the one on pelvic floor contraction, and length of total second stage. Women with a smaller hiatal area on pelvic floor contraction, indicating a stronger pelvic floor muscle, had a longer second stage of labor [29].
Interestingly, fetal weight was not associated with LA volume. However, the fetal station was associated with a decreasing levator volume. The lower the fetal station/head, in centimeters to the levator ani, the thinner the LA muscle appeared. After adjusting for maternal BMI, this relationship disappeared.
A longitudinal study could answer the question whether the thinning is an effect of pregnancy or whether imaging has more artefacts in pregnancy due to baby movements or measuring technique.
It is not elucidated yet whether it is beneficial for the pelvic floor health in later life to have a strong and thick pelvic floor musculature before pregnancy, that might lead to a longer second stage of labor, which however, may be associated with a higher rate of pelvic floor trauma, or whether a primarily weaker pelvic floor with a larger hiatus and shorter parturition time has lower negative sequelae later in life.
A randomized controlled trial involving 200 women evaluated the possible prevention of pelvic floor disorders using stretching of pelvic floor muscles with the balloon device Epi-No® in late pregnancy. The rationale is based on sports physiology where an increased muscle extensibility might be obtained by intermittent stretching before the exertion. In this trial a non-significant reduction in levator ani muscle avulsion after training with Epi-No®, beginning at 37 weeks’ gestation (6 % vs. 13 %) was found [31]. It is to mention that this study was insufficiently powered with 200 patients included instead of the 660 women that would have been needed according to a power calculation that was aimed to show a 50 % reduction in the incidence of levator avulsion.
Biomechanical Models
Computational models have been demonstrated to be an effective tool in investigating the processes during the first and second stages of parturition. The pelvic floor and the associated structures are one of the most complex regions of the human body and undergo immense stretching in the course of pregnancy and even more during parturition.
Animal models have the inherent problem of the lack of upright position, which is an important factor in studying the pathophysiology and natural history of prolapse. Interdisciplinary collaborative research, involving bioengineers and clinicians, is essential to investigate and simulate the mechanical effects on the pelvic floor along gravity [32]. Geometrical information is gained from high-resolution images, mostly generated by MRI, and processed by segmentation into a finite element by a mathematical tool. The finite element method discretizes a continuous model into small pieces to investigate their mechanical behaviour under load or stress. This has been done by several authors simulating delivery [33–35] or prolapse [36, 37], though no biomechanical models simulating the changes during pregnancy are available yet.
Anatomical Changes of Ligaments
Landon et al. showed that fascia in pregnant women stretches to a much greater length but had less tensile strength compared with fascia from nonpregnant women [38]. The authors demonstrated that the collagen structure changes and the connective tensile strength decreases during pregnancy. The loosening of connective tissue in ligaments and fascia yields to common symptoms like symphysis pubic dysfunction and pelvic girdle pain. The levels of the hormone relaxin were found to be significantly higher in pregnant women that have bothersome joint pain and laxity [39]. Whether there is a relationship between pelvic girdle pain and specific pelvic floor disorders like prolapse is not elucidated yet.
Bladder and Functional Bladder Neck Anatomy during Pregnancy
Epidemiological studies show an increase in lower urinary tract and pelvic floor symptoms during pregnancy [40]. Pregnancy affects bladder function adversely. Urinary incontinence is seen more often in pregnant women than in matched controls and the mean prevalence of stress urinary incontinence (SUI) during pregnancy can be as high as 41 % (18.6–60 %) and increases with gestational age [41].
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