Benefits of Assessment of the Lower uterine segment in predicting a successful trial of labour in women with a history of one previous caesarean section

With the rising amount women giving birth by caesarean section in the
Netherlands and beyond, there is also an increase of women having a trial of
labor after caesarean. Vaginal birth after a previous caesarean section had a
lower success rate and is associated with a high rate of repeat caesareans and
a higher risk adverse events for mother and fetus.
A rare but devastating complication is a uterine rupture. A recent review
showed a relation between the thickness of the lower uterine segment and risk
of scar defects and dehiscence. Differences between the way of measuring and
the primary outcomes have made it difficult to compare the existing literature.
Several attempts have been made to develop a prediction model for successful
VBAC, all based on maternal characteristics, medical history, none of them have
taken into account the aspects and thickness of the lower uterine segment.

To develop a prediction model for women with one previous caesarean section by
combining assessment of the lower uterine segment with an extensive antepartum
history taking and postpartum follow up.

We will perform a closed observational cohort study, that is, the results of
the measurement of the lower uterine segment will not be communicated to either
patient nor obstetric health care provider.
We recruit pregnant women referred to the AMC early in pregnancy for routine
first trimester ultrasonography. Patients with a singleton pregnancy and with
one previous CS are counselled to undergo lower uterine measurement in
succesion of routine ultrasonographic examinations during pregnancy.
Exclusion criteria are previous myomectomy or prior classical caesarean
Eligible women give written informed consent and approval is attained from the
METC of the AMC.
Eligible participants undergo routine ultrasound examination and additional
transvaginal measurement of the lower uterine segment in 1st , 2nd and 3rd
trimester.
Lower uterine segment evaluation is performed by transvaginal ultrasound with a
transvaginal 7 MHz frequency probe. All ultrasound assessments are performed
by experienced physician-ultrasonographists appropriately trained in performing
this measurement. The examinations are performed with a near empty bladder. A
clear view of the LUS view is obtained in the midsagittal plane. The first TVU
is performed in the 12 week of pregnancy. This examination we try to identify
the uterine scar and measure the dimensions of the scar. Figure *
During 2nd and 3rd trimester LUS examination of the lower uterine thickness
will be performed in week 20 during the fetal anatomy screening examination an
in week 34 together with biometry assessment.
A sagittal scan from side to side is performed and the thinnest measurement
from the mucosa of the bladder to the chorioamniotic membrane as taken up to a
tenth of a millimetre.
During the first trimester extensive history will be taken and data is
collected concerning prior pregnancy outcomes. During the concurrent
examination developing pregnancy related complications are noted. The mode of
delivery is chosen solely based on the judgement of the obstetric caregivers
who are blinded for LUS measurements. After delivery pregnancy outcomes are
retrieved.

Women will undergo in succession to the routine scans in 1st 2nd and 3rd
trimester transvaginal sonographic evaluation of the lower uterine segment.
This can be done within 5 minutes time. Women will in general have no
discomfort during examination and there are no associated risks concerning the
pregnancy.