A few studies have reported anatomical changes in levator hiatal dimensions by 3D transperineal ultrasound through gestation,15,17 but to date, there is a lack of longitudinal studies monitoring the changes in contractility and distensibility of PFM . In addition, these studies did not investigate the influence of maternal hyperglycemic environment on changes of PFM function just before the GDM diagnosis and throughout gestation. Therefore the aim of this study was To investigate the effect of gestational diabetes mellitus (GDM) on pelvic floor muscle (PFM) contractility and distensibility at two-time points of pregnancy by transperineal three-dimensional (3D) ultrasound.

Prospective cohort study conducted between 2015 and 2016 was approved by the Research Ethics Committee of the Institution (Protocol Number 972.104). After the knowledge of all procedures a written informed consent was obtained from all subjects. Helsinki Declaration on human experimentation guidelines was respected.
The inclusion criteria were pregnant women in their first  or second pregnancy with previous elective Cesarean-section,  18-40 years of age, singleton pregnancy and GDM or normoglycemia diagnosis.18 The exclusion criteria were previous Diabetes Mellitus (type I or II or overt diabetes), multiple pregnancy, previous history of labor during the first pregnancy and/or previous vaginal delivery, prolapse or antiincontinence surgery, PFM training before or during pregnancy, connective tissue diseases, neurological disorders, fail to perform appropriately the sequence and correct mode of PFM contraction and Valsalva maneuver, and inability to perform a maximal Valsalva maneuver for cardiac or pulmonary disease.
The sample size calculation was performed using results from a pilot study in which 35 pregnant women normoglycemic and 35 women with GDM were required to detect a 5% change in levator hiatal area (LHarea) with a two sided α of 0.05 and a power of 80%. We included 44 GDM women (GDM group) and 60 normoglycemic pregnant women (NG group) at 24-30 weeks of gestation to preserve the power, taking into account the possibility of women dropout.

Personal, clinical, Obstetric and anthropometric data was collected. Transperineal 3D ultrasound was performed at two-time points , between 24-30 weeks of gestation and 36-40 weeks of gestation, in the supine lithotomy position after voiding, using the GE Voluson “I” system with RAB 2-6RS(2-6 MHz) curved array 3D transducer (GE Healthcare, Zipf, Austria). The field of view angle was set to its maximum of 70° in the sagittal plane and 85° in the coronal plane.16,19 Imaging data sets were taken at rest, during maximal voluntary PFM contraction and during maximal Valsalva maneuver by a trained and experient investigator (CISF) in transperineal 3D ultrasound and differentiated by colors. The images at rest were acquired only as a basal measure to calculate the function index variables. 
The ultrasonographic images were stored offline by anonymous code numbers. Analysis of the LH dimensions  were carried out using 4D View – version 14 Ext 3 (GE Healthcare) software program and all data sets were analyzed in random order, which was blinded to all participant data. All measurements of the LH area were determined in the axial plane of minimal hiatal dimensions, identified in the mid-sagittal image as the minimal distance between the inferior margin of symphysis pubis and the anorectal junction, using render mode. Volume rendering is a technique used to display a two-dimensional projection of a 3D structure. 27 The area of the LH (LHarea) in cm2.

A total of 83 participants were included in the final analysis, 38 in GDM group and 45 in NG group. Table 1 shows baseline variables. Table 2 compares Absolute Values at  24-30 Weeks of Gestation and 36-40 Weeks of Gestation and on Gestational  Progress of Levator Hiatal Area.

A new and interesting finding of our study is that GDM had negative impact on PFM with decrease in contractility, distensibility and mobility. Analysis of our results showed a weak muscle at 24-30 weeks of gestation, demonstrated by a larger LHarea during contraction, meaning a less muscle contractility. The increase of these dimensions during contraction is inversely proportional to contractile function capacity of the muscle. A soft muscle was identified at 24-30 weeks of gestation, showed by a larger LHarea on distension and although this distension has been considered a physiological adaptation in pregnancy, in GDM group it was deeper. At 36-40 weeks of gestation we found a smaller LHarea during distension characterizing a stiff muscle with less muscle distensibility.

In conclusion, based on these results, we identified that GDM have a relevant impact on pelvic floor function detected by 3D ultrasound , characterized by decrease in contractility, distensibility from 24-30 to 36-40 weeks of gestation