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Uterine cicatrix. Risk assessment

In this survey, we would like to share the existing information on uterine cicatrices, the risks of rupture of such uteri, the choice of a delivery method after caesarean section and the prognosis of the “quality” of a cicatrix in general. 

The situation with cicatrices in our country somewhat resembles that with polymorphisms of hemostasis system genes. The evaluation of the necessity of investigation of these polymorphisms as well as of their clinical significance and, most surprisingly, the choice of a therapy method are a matter of preference and allegiance of a doctor or a medical institution rather than a result of a strict adherence to evidential documents and protocols.

So how is a uterine cicatrix assessed globally?

First of all, let us take a look at some terms. These are something we can’t do without.
  • TOLAC/TOL (trial of labour after caesarean delivery) is an attempt of spontaneous delivery after a preceding caesarean section. This is a situation when delivery starts off as a vaginal one but something goes wrong and doctors have to perform a caesarean section. 
  • VBAC is a vaginal birth after a caesarian section. This is a situation when everything works out well: labour starts and ends the way it is dictated by nature.  
  • ERCD is an elective repeat caesarean delivery. It includes women whom a caesarian section as a delivery method was offered to from the very beginning.   

All cases deal with the second (or the third) pregnancy after a caesarean section, i.e. when a woman already has a cicatrix on her uterus. 

We will now talk numbers just to understand how many women could find this information interesting. 

About 1.5 million caesarean sections are performed in the world per year. The per cent of performed caesarean sections varies greatly between different countries – from 15% in the Netherlands to 40% in Italy. The rate of vaginal delivery after a preceding caesarean section is variable as well – from 5% to 30%. The main indication for a caesarean section is still a previous caesarean section. What does it mean? First of all, that there are no common approaches to the choice of a delivery method in women with a uterine cicatrix. Second, this situation gives an opportunity for the development of protocols of pregnancy management in women with a uterine cicatrix that would evaluate a patient’s medical history, specific features of the ongoing pregnancy, hospital resources, health insurance availability etc. This work is carried out and quite successfully at that. At many hospitals, the rate of caesarean sections goes down. 

There is another type of clinical work that is gaining momentum in our country: the evaluation of the quality of a cicatrix and the prognosis of pregnancy course and delivery BEFORE pregnancy. Or even more drastically: the practice of allowing or forbidding pregnancy based on the US features of a cicatrix. This aspect is of particular interest to us, the fertility specialists, who INDUCE pregnancy by transferring an embryo into the uterine cavity, i.e. who supposedly take on responsibility for a potential uterine rupture… 

Let’s try to figure out whether it is indeed the case or if we are again biting off more than we can chew…

At the end of the article there will be links to the materials that I have used to write this piece. If you have a keen interest in this subject, you can read about it in the original in more detail. In this article, however, I will take the liberty of providing a summary of these documents. The documents that were written in very different countries but that, surprisingly, do not contradict each other…

Now then, what matters are brought up in these documents?

What per cent of women will successfully deliver after a C-section?

What consequences do TOLAC, VBAC and ERCD have for a woman and her child?

Where can we find the instrumental and clinical parameters that could be adopted as strict prognostic factors for the unfavorable development of a cicatrix?

It is thought that about 70% of women with a uterine cicatrix who take on vaginal labour will deliver vaginally. But this is a very averaged rate. There are factors improving one’s prognosis and factors aggravating it. 

The former include:
  • A medical history of a vaginal delivery;
  • A C-section performed due to fetal malposition; 
  • Tertiary healthcare;
  • A C-section in the lower uterine segment;
  • The mother’s young age;
  • BMI of less than 30;
  • A spontaneous beginning of labour earlier than 40 weeks;
  • The uterine cervix dilated by more than 4 cm;
  • Fetal weight of less than 4 kg;
  • The absence of gestosis in the second half of pregnancy (preeclampsia);
  • The possibility of labour management with FHR-monitoring. 

The latter include:
  • A classical caesarean section;
  • Late reproductive age;
  • An overdue pregnancy;
  • Fetal weight of more than 4 kg;
  • A low Bishop’s score at the assessment of cervical ripening;
  • An interdelivery period of less than 18 - 24 months;
  • A single-layer uterine closure;
  • A C-section due to fetal distress, weak labour, discoordinated delivery;
  • The necessity of labour induction;
  • A medical history of three C-sections;
  • Conservative myomectomy with the opening of the uterine cavity; 
  • A complex uterine surgery. 

At the same time, none of the above-mentioned criteria are reliable for the prognosis of uterine rupture. You might have noticed that there was no mention of cicatrix visualization via/by means of a US investigation; of hysteroscopy or hysterosalpingography. These are certainly carried out but the connection between the cicatrix thickness, a niche and the risk of rupture has not been proven. 

There are good articles with a good design that suggest assessing the lower uterine segment thickness and the myometrium thickness in the cicatrix area at 34 - 39 weeks of pregnancy as well as choosing a delivery method based on the condition of a cicatrix, but definitely not before pregnancy delivering a verdict whether a patient is allowed to get pregnant or not. There is also a management algorithm for patients with a HISTORY of uterine rupture during a previous pregnancy.

As for the consequences for a mother and a child after any of the delivery variants, the following can be outlined:

The maternal mortality in case of TOLAC - 1.9 per 100000, in case of ERCD — 9,6 per 100000.

The risk of rupture of a cicatrix in case of TOLAC - 0.28-0.77%, in case of ERCD – 0,009 – 0,22%.

Numerous C-sections are a proven risk factor for infertility, early menopause, adhesive process, placenta previa and placenta accreta. 

The perinatal mortality in case of TOLAC - 1,3 per 1000, in case of ERCD — 0,5 per 1000.

The documents deal with a lot more rates, and here we have looked only at the most illustrative and much-discussed ones. 

In essence, one must understand that these complications are extremely rare and do not occur as often as one might expect, considering the interest doctors in Russia show in a detailed description and assessment of a uterine cicatrix during pregnancy planning. Truly, we cannot establish standard values of cicatrix thickness either before or during pregnancy. The only two proven signals of cicatrix deficiency are local painfulness in the cicatrix area and/or the impaired condition of a fetus. These are indeed signs of an imminent catastrophe!

So what can we suggest? 

Very often, a delivery method is chosen by a patient based on her own preferences and not by a doctor judging from the clinical situation. Or alternatively, by a doctor, but based on what is more predictable or what is common in a given hospital.

Both of these practices are a far cry from a medical approach. Which is why in the second half of all guidelines it is suggested that:

A form containing information about a previous caesarean section (reasons for a C-section, specific features of the course of pregnancy as well as of the postoperative period) should be adopted so that a woman would not have to rack her memory trying to answer why she had a C-section.

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