Materials and Methods

The current study was a secondary analysis of a prospective study that aimed to evaluate the association between sonographic LUS thickness and uterine rupture. It was conducted between 2004–2006 in the Department of Obstetrics and Gynecology of Sainte-Justine Hospital (Montréal, QC, Canada). Women with singleton pregnancy in cephalic presentation between 35 ^0/7 –38 ^6/7 weeks of gestation and who had 1 previous cesarean section were included.

The study was approved by the institutional ethics committee, and participants gave their written informed consent. The original study design has been described in detail in a previous publication.

We recorded maternal characteristics, medical and reproductive history, and characteristics of the previous cesarean. Type of closure, including the number of layers and type of suture, were noted from the previous operative report when available. Sonographic examinations were undertaken with an Aloka SSD 5500 system (Aloka Co, Ltd., Tokyo, Japan).

LUS was measured transabdominally, with repeated transvaginal assessment if not well visualized. Sonographically, the normal LUS is a 2-layered structure consisting of an echogenic layer (including the bladder wall) and a usually less echogenic layer (considered to represent the myometrium).

Transabdominal measurements were recorded when the bladder was full (ie, when bladder fullness was felt): the LUS was examined longitudinally and transversely to identify any areas of obvious uterine scar dehiscence. The thinnest LUS zone was identified, and the area magnified. Full LUS thickness was measured with a cursor at the interface between the urine and bladder wall and at the interface between the amniotic fluid and decidua ( Figure ). The myometrium was measured with the cursor at the interface of the bladder wall and the myometrium so that it included only the hypoechogenic layer ( Figure ). When the LUS was not entirely visualized until the cervix, or if maternal tissues impeded good visualization, the measurement was repeated transvaginally.

Measurement of the LUS thickness

In this case, the full LUS was 2.5 mm, whereas the myometrial layer was evaluated at 0.9 mm.

Jastrow. Labor at prior cesarean on LUS thickness in subsequent pregnancy. Am J Obstet Gynecol 2010.

Again, the LUS was examined longitudinally and transversely, and the thinnest zone was identified and assessed. At least 3 measurements were taken, and the lowest value was retained as the dependent variable. The choice to keep the lowest value was based on previous publications.

One observer, a maternal-fetal medicine (MFM) subspecialist, performed all the measurements. As described in the original study, an ultrasound technician was asked to measure the full LUS blinded to the results of the MFM subspecialist, and the interobserver reproducibility was calculated.

We reviewed the literature and identified potential factors that could be associated with LUS thickness, including maternal age (categorized as younger than 30, 30–39, and 40 years old or older); gestational age (35–36 weeks and 37–38 weeks); body mass index (categorized as <25, 25–29, 30–34, and ≥35 kg/m ² ); diabetes mellitus (gestational, type 1 or 2) during the current pregnancy; prior vaginal delivery; previous VBAC; prior preterm delivery (defined as delivery before 37 weeks of gestation); interdelivery interval (defined as the number of months between the previous cesarean and the expected date of delivery of the current pregnancy, categorized as less than 18, 18–23, and 24 months or more); type of uterine closure, including the number of layers (single vs double); type of suture used (chromic catgut vs vicryl/polysorb); the indication for previous cesarean section (divided into recurrent indication, such as arrest disorder, and nonrecurrent indication, such as breech or fetal distress); and labor during prior cesarean (categorized as no labor, latent phase [defined as ≤4 cm of cervical dilation] or active phase, [defined as >4 cm of cervical dilation]); and birthweight at previous cesarean and at delivery in the current pregnancy (categorized as <2500, 2500-3999 g, and ≥4000 g).

These factors were considered by univariate regression analysis, and all significant factors with P < .10 were included in a multivariate linear regression analysis. Logistic regression analyses were performed to identify factors associated with full LUS thickness below 2.3 mm. The choice of this specific cutoff was based on our previous publication.

Spearman’s correlation analyses were performed between cervical dilation at the time of cesarean and LUS thickness. Finally, Wilcoxon and McNemar tests were used to compare LUS thickness between abdominal and transvaginal assessments.

Statistical analyses were conducted with SPSS 13.0 (SPSS, Inc, Chicago, IL), and P < .05 was considered significant. However, in the univariate analyses for factors related to LUS thickness, because 14 variables were tested, we performed a Bonferroni correction to avoid type 1 error. A P < .004 (.05 per 14 individual tests) was considered significant for those analyses. The sample size was limited to the number of women recruited in the original study.

Results

We recruited 235 women with a single prior cesarean at a mean gestational age of 36.7 ± 1.3 weeks. LUS thickness was measured by the transabdominal approach for all patients, and transvaginal assessments were required in 112 women (48%). Patients who had a transvaginal assessment were not statistically different from the whole group in terms of demographic characteristics, such as maternal age, gestational age, body mass index, and presence/absence of labor at the previous cesarean.

Full LUS was slightly thicker with the transvaginal approach compared with the transabdominal approach (median, 3.2 mm; interquartile [IQ], 2.4–4.2 vs 3.0 mm; IQ, 2.4–3.6; Wilcoxon test: P = .03), but there was a high rate of agreement for LUS thickness less than 2.3 mm (83%, McNemar test: P = 1.00). Full LUS thickness data were available for all patients (n = 235), and myometrial measurement was obtained for 222 of them (94%). The median of full LUS and myometrial thicknesses was 2.8 mm (IQ, 2.1–3.4) and 1.3 mm (IQ, 1.0–1.9), respectively. As described in the results of the original study, the proportion of agreement between the 2 observers was 83%, and the kappa coefficient was judged as moderate (0.57).

Table 1 reports full LUS and myometrial layer thicknesses for each evaluated factor. Prior cesarean for a recurrent reason and cesarean during the active phase of labor were associated with a thicker full LUS. In regard to the myometrial layer, prior cesarean for a recurrent reason or during the active phase of labor was associated with a thicker measurement.

TABLE 1

Factors associated with sonographic measurements

Variable	n	Full thickness in mm(median and IQ)	P value	n	Myometrial layer in mm(median and IQ)	P value
Maternal age at delivery, y
<30	78	2.5 (2.0–3.2)	.02	74	1.3 (0.9–1.7)	.02
30–39	147	3.0 (2.2–3.8)		138	1.4 (1.0–2.1)
≥40	10	2.6 (2.2–2.9)		10	1.1 (0.8–1.3)
Body mass index, kg/m 2 (n = 230)
<25	28	2.8 (2.1–3.4)	.90	27	1.3 (0.9–2.0)	.91
25–29	110	2.8 (2.1–3.3)		106	1.3 (0.9–1.9)
30–34	62	3.0 (2.2–3.6)		59	1.3 (1.0–1.9)
≥35	30	2.8 (2.5–3.3)		26	1.5 (1.1–1.8)
Diabetes mellitus
No diabetes	208	2.8 (2.1–3.4)	.73	199	1.3 (1.0–1.9)	.21
Gestational	22	2.8 (2.2–3.3)		20	1.2 (0.9–1.6)
Type 1 or 2	5	3.2 (2.3–3.7)		3	2.0 (1.4–2.0)
Gestational age, wk
35–36	109	2.9 (2.2–3.4)	.60	104	1.4 (1.0–1.9)	.55
37–38	126	2.7 (2.1–3.4)		118	1.3 (0.9–1.9)
Prior vaginal delivery
Yes	33	2.8 (2.1–3.7)	.77	29	1.2 (0.9–2.2)	.68
No	202	2.8 (2.1–3.4)		193	1.4 (1.0–1.9)
Prior VBAC
Yes	19	2.4 (1.9–3.5)	.57	17	1.1 (0.5–1.4)	.34
No	216	2.8 (2.2–3.4)		205	1.4 (1.0–1.9)
Prior preterm delivery
Yes	27	2.5 (2.1–3.3)	.61	27	1.1 (0.9–1.8)	.78
No	207	2.8 (2.1–3.4)		194	1.4 (1.0–1.9)
Unknown	1	3.1		1	1.3
Prior cesarean for recurrent indication (arrest disorders)
No	124	2.5 (2.0–3.2)	.001	119	1.2 (0.8–1.7)	.003
Yes	110	3.0 (2.4–3.8)		102	1.5 (1.1–2.0)
Unknown	1	4.2		1	1.9
Labor at prior cesarean
No labor	43	2.4 (2.0–3.2)	< .001	40	1.2 (0.7–1.6)	< .001
Latent phase (dilation <4 cm)	38	2.8 (2.–3.3)		37	1.4 (1.0–1.8)
Active phase (dilation ≥4 cm)	114	3.1 (2.5–3.9)		105	1.5 (1.1–2.2)
Unknown	40	2.4 (1.9–3.0)		40	1.1 (0.8–1.5)
Interdelivery interval, mo
<18	19	2.8 (2.2–3.6)	.82	18	1.6 (0.9–2.0)	.25
18–23	30	2.6 (2.1–3.2)		28	1.0 (0.8–1.7)
≥24	185	2.8 (2.1–3.4)		175	1.4 (1.0–1.9)
Unknown	1	2.5		1	0.9
Type of uterine closure at previous cesarean
Single layer	38	2.6 (2.0–3.2)	.35	34	1.2 (0.8–1.5)	.11
Double layer	165	2.8 (2.2–3.4)		160	1.4 (1.0–1.9)
Unknown	32	2.6 (2.0–3.9)		>28	1.5 (0.9–1.9)
Type of suture used for uterine closure at previous cesarean
Chromic	134	2.6 (2.1–3.2)	.06	128	1.3 (1.0–1.7)	.08
Synthetic	51	3.1 (2.2–4.0)		49	1.5 (1.0–2.2)
Unknown	50	2.7 (2.1–3.8)		45	1.5 (1.0–1.9)
Birthweight, g
<2500	6	3.1 (2.5–4.0)	.07	5	1.6 (1.5–2.3)	.11
2500–3999	187	2.8 (2.1–3.4)		178	1.3 (1.0–1.9)
≥4000	29	3.0 (2.2–3.9)		26	1.7 (1.0–2.2)
Unknown	13	2.5 (1.8–2.7)		13	1.1 (0.9–1.5)
Birthweight at previous cesarean, g
<2500	27	2.5 (2.1–3.3)	.35	27	1.1 (0.9–1.8)	.73
2500–3999	178	2.8 (2.–3.3)		166	1.4 (1.0–1.8)
≥4000	29	2.9 (2.4–4.0)		28	1.6 (0.9–2.2)
Unknown	1	3.1		1	1.3

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Provider knowledge, attitudes, and treatment preferences for early pregnancy failure
2. Tissue tumor marker expression in smokers, including serum cotinine concentrations, in women with cervical intraepithelial neoplasia or normal squamous cervical epithelium
3. Maternal and paternal race/ethnicity are both associated with gestational diabetes
4. Discussion: ‘Early menstrual characteristics and endometriosis’ by Treloar et al

Stay updated, free articles. Join our Telegram channel

Join