 Sonological determination of the third trimester lower segment uterine scar integrity. So, what do we mean by the lower segment of the uterine body? The lower segment is the constricted part of the uterus which lies between the body of the uterus and the cervix. In a normal lady, this part or the isthmus is about 0.5 to 1 cm in length. But during pregnancy, this starts expanding or lengthening and it starts thinning out as we can see in the diagram. And by the time it's term, the isthmus of the uterus measures around 2.5 cm. So, why is it important for us to measure the scar thickness or the lower uterine segment thickness? In the present days, there is an increase in the number of the caesarean deliveries. There is also an increase in the intrapartum uterine rupture especially because people are opting for vaginal birth after caesarean deliveries. So, what happens is because of the risk of the rupture, people start opting for an elective caesarean delivery. But is there a way that we can still suggest the lady to go into labour? We can still give them the option of safe labour. It is possible if we are able to select a good candidate for the trial of labour. And this is possible if we are able to assess the lower segment scar thickness and predict the outcome that would occur when the lady goes into labour. This is one of the studies and it shows that there is a very high propensity for uterine rupture. There are two words that we are seeing. We come across two words in this that's uterine rupture and uterine dehiscence. We will see what does the difference between them. Uterine dehiscence is when there is an incomplete disruption of the uterine scar. It does not penetrate the cirrhosa and this is not clinically significant. The mother may present, may or may not present with pain. However, uterine rupture is when there is a complete disruption of all the uterine layers including the cirrhosa. And this is life-threatening not only for the mother but for the baby also. And most often we do not come across a patient with uterine rupture because the patient immediately collapses and goes into hyperbolemic shock. So this is an image which is showing the integrity of a scar. It is naturally thinned out as compared to the rest of the myometrium. But when it undergoes a dehiscence there is a ballooning you can see but you do not see that there is a complete disruption. And in uterine scar rupture you are actually seeing a complete dehiscence of the scar. So the same thing we are able to see in intra-op images we are seeing the uterine scar dehiscence which is an intra-operative image and the other one is the uterine rupture which is an image from the journal where you can see that the entire fetus or the amniotic cavity has come out of the uterus. So the questions that we need to answer here are when, where, how, what to measure and which is a normal scar and what constitutes scar thinning or scar rupture. So when to measure ideally we should measure it in the third trimester say by 36 to 38 weeks. However if the lady presents any time earlier with scar tenderness or pain we need to assess the scar site. There are also studies which are ongoing in which they are doing a scar thickness assessment in the second trimester to be able to assess if it will help predict the scar rupture or scar dehiscence in the later part of the pregnancy. Next important thing is the location of the scar site. The scar location is largely dependent on the degree of the cervical effacement that would have occurred during the previous caesarean section. The incision should ideally pass through the isthymus of the cervix if the cervix is not effaced. But if the caesarean has been done when the female was having a uterine contraction then the scar site would have passed through the cervical tissue as has been shown in the image. And many times we are not able to identify the location of the scar. In such scenarios we take multiple thin measurements of the lower uterine segment and an average of the same or the thinnest of these is calculated. So how do we measure? There are two options. We can do a trans abdominal or a trans vaginal scan. The lower segment scar thickness is actually a two layer structure there are two terms again. Either it can be a lower segment scar thickness or a myometrial thickness. When we see a lower segment scar thickness we mean it's a two layer structure which is an echogenic layer of the bladder wall and then there is a less echogenic myometry. When we go through a trans abdominal approach we need to have a bladder which is over-distended and you look at the lower uterine segment you take a large view look at the lower uterine segment in the mid sagittal section then magnify the image in such a way that you are able to focus only on the lower uterine segment and the calipers when placed would not make a change of more than 0.1 millimeters. This would give you the thinnest to be able to accurately calculate the thinnest zone and will reduce the error rate. When we go for the trans vaginal scan we know the bladder should be empty but it can be partially distended also to be giving us a very good difference in the image and again we need to take a large view where we are including the mid sagittal image with the cervix included we are able to identify once we identify the lower segment section we are supposed to magnify identify the scar magnified such that 75 percent of the image is inclusive of only the scar again to reduce the error rate when we are placing our curses so what is constituted by the scar when we say a scar thickness we could be talking of two different terms one is a lower segment scar thickness and the second is a myometrial thickness. What is the difference between them? This image represents both of them. When we say myometrial thickness we mean just what the name suggests it is exclusively the myometrium that we are calculating but when we are talking about the lower segment scar thickness we are talking about the myometrium and the bladder mucusa both of them together is forming the lower segment scar thickness accordingly we can understand the cutoff of both these thicknesses would be different lower segment scar thickness should be more than 2.5 mm and the myometrial thickness should be more than 2 millimeters this is again a study which shows that the optimal or the lower limit cutoff for a lower segment scar thickness is 2.5 mm and for the myometrial thickness is 2 mm so this is zoomed in image which is showing the layers that we are encountering when we look at the scar when we go from inside out that is from the fetal end to the maternal end one is the fetal skull two is the fetal skull three is the amniotic fluid four is the amniotic membranes the membranes in the decidure five is the myometrial myometrium which we are measuring as the myometrial thickness and six is the bladder mucusa so when we measure the five and the six together it becomes a lower segment scar thickness so what are the things that we are looking for we are looking for the scar thickness which I mentioned should be if you are taking it as lower segment scar thickness it should be more than 2.5 mm and if you are taking it as myometrial thickness it should be more than 2 mm if we go to grade the lower segment scar thickness as mild moderate and severe then the thickness would be about 2.5 mm to 3.5 mm becomes as a mild thinning 2 to 2.5 mm becomes moderate thinning and less than 2 mm becomes significant thinning the scar shape should be ideally triangular as we would expect because there is a some amount of fibrosis but we should ensure that there is no ballooning that occurs we have to ensure the scar continuity which is very obvious scar ecotexture also needs to be assessed because heterogeneity in the scar is again suggesting the possibility that the scar is not healthy so what are the things that we are assessing in these parameters a scar shape like I mentioned should be ideally triangular but the most important thing is we have to see that there is no ballooning in that area when we look at the lower segment scar thickness 2.5 to 3.5 mm is acceptable more than 3.5 mm is acceptable myometrial thickness about 2 mm is ideal we have to see if the scar continuity is there or not we have to make a comment on that which is a very obvious one because if there is no scar continuity there is a utrient rupture then definitely the patient is in a severe significant hypovolemic shock already we have to make a note about the ecotexture of the lower utrient segment and we have to be able to comment what happens to the scar when the fetus moves because at times when the fetus moves or when there is a pressure which occurs there can be a transient ballooning that occurs because of fetal movement and a comment has to be made about that also so these are some examples the first image is adapted from one of my friends so that shows a paper thin scar you can see that the scar is significantly thinned out if you look at the myometrium alone and you can see that along with the bladder mucosa there is a relative thickness seen here when we measure the myometrium alone it is significantly thinned out in the same way in the lower TBS images we can see that there is significant myometrial thinning this is an example where we can see that there is so much thinning and that there is a behescence there is ballooning of the membrane that is seen you can see the fetal head you can see the ballooning of the membranes that is occurring and this is uterine dehiscence this is another case of ballooning or uterine dehiscence and this was the corresponding intro of images which was demonstrating the ballooning so what do we see is a good quality scar a good quality scar is when the scar thickness is optimal about 3.5 mm then there is nothing we need to be worried about that scar is homogeneous it is triangular in shape it is not always possible for us to demonstrate the triangular shape but if it is not ballooned out that is good enough and they also say that in some studies they have made a comment about qualitatively richer perfusion around the scar not all the machines are having the capability to demonstrate vascularity at the scar side a richer perfusion suggests that it is a more stable or more well integrated scar so what is basically the take home message in this particular talk is that there is a strong inverse correlation between the lower uterine segment thickness and the risk of the mother developing a scar disruption so the thinner the scar the higher the chance of the disruption integration of lower uterine segment thickness is very important in the decision making about the root of delivery in these kind of patients who have undergone a previous cesarean delivery and we need to plan out what should be done in this present delivery it is very important that this strategy is instituted as it has a potential to lead to a reduction of the lower segment cesarean sections in women who had prior cesarean sections by reassuring the women and clinicians about the relative safety of trial of labour after cesarean section so it is very important that we integrate measurement of the scar thickness in the decision making of these patients so what are the red flags once again as just to repeat lower uterine segment thickness less than 2.5 mm and diameter thickness less than 2 mm ballooning of amniotic membranes are the red flags which should definitely make us inform the clinician immediately about the chances of scar rupture these are some of the articles I have taken the reference from and the treatment without prevention is simply unsustainable it is extremely important that we use the information that we get in trying to help the patients and plan out the right way of treatment and take the pregnancy up to the delivery in a healthy and safe manner thank you