Morphological Changes in Rectus Abdominis Muscle Associated With Pregnancy and Abdominoplasty

Abstract

Background

Pregnancy can alter the rectus abdominis, but abdominoplasty can potentially correct these changes.

Objectives

The aim of this study was to examine these muscle changes during pregnancy and to evaluate how effectively abdominoplasty with double folds of the rectus abdominis tightens the muscle.

Methods

Clinical data were obtained from nulliparous and pregnant patients who had undergone abdominoplasty with double folds of the rectus abdominis. Measurements were made of linea alba width, rectus abdominis width, thickness, and cross-sectional area, and abdominal circumference. Postoperative complications were also recorded. Patient satisfaction with the morphology of the rectus abdominis, both pre- and postsurgery, was assessed on a 5-point Likert scale.

Results

The study included 400 women: 171 nulliparous, 106 with 1 pregnancy (Group 1), and 123 with 2 or more pregnancies (Group 2). Complete postoperative data were available for 32 patients (Group 3). Significant widening of the linea alba was found in Groups 1 and 2. The rectus abdominis width increased significantly in Group 1 but not in Group 2. Its thickness remained unchanged in Group 1 but decreased in Group 2, mirroring the pattern of its cross-sectional area. In Group 3, both the linea alba and rectus abdominis width decreased, while thickness and cross-sectional area increased. Satisfaction with muscle morphology improved significantly postsurgery, with no serious complications reported.

Conclusions

Pregnancy can cause the rectus abdominis muscle to separate, widening the linea alba and flattening the muscle. Abdominoplasty, which reinforces the muscle with double folds, effectively resolves this, resulting in high patient satisfaction and few complications.

Level of Evidence: 3

The rectus abdominis, a fundamental component of the abdominal musculature, plays a crucial role in abdominoplasty procedures. Various factors, including pregnancy, can compromise the strength of the abdominal wall, resulting in conditions such as rectus diastasis (RD) and the protrusion of abdominal contents, known as ventral hernia. Should the rectus muscle fail to adequately recover postdelivery,¹ enduring alterations in both appearance and function may ensue, exacerbated by age-related increases in fibrous tissue and reductions in muscle elasticity and flexibility.² Evolving fertility policies in China have led to a rise in pregnancies among women of advanced maternal age and those with multiple pregnancies, thereby increasing the demand for abdominoplasty. This surgical intervention aims to fortify the rectus muscle and address morphological alterations, including RD. Nonetheless, postpartum morphological changes of the rectus muscle remain inadequately understood, particularly regarding variations across different populations and ethnic groups. Consequently, this study seeks to elucidate the morphological transformations of the rectus muscle following pregnancy and assess the impact of abdominoplasty, specifically focusing on the double-fold technique of the rectus abdominis, to furnish clinical evidence for the advancement of abdominoplasty practices.

METHODS

Study Population

Ethical approval for this study (Ethics Committee No. 202464) was provided by the Ethics Committee of Xi’an International Medical Center Hospital. We recruited female patients who underwent abdominal computed tomography (CT) examination between October 2022 and February 2024 in our hospital. For nulliparae, the exclusion criteria were as follows: (1) age 18 years and younger; (2) history of abdominal trauma and major surgery (including all abdominal operations); (3) acute abdominal disease that might affect abdominal muscle contraction (including but not limited to acute cholecystitis, acute appendicitis, acute peritonitis, and acute gastroenteritis); (4) incomplete clinical data. In addition to the above exclusion criteria, patients after postpartum abdominoplasty were excluded if: (1) they did not receive rectus abdominis plication; (2) they had incomplete postoperative follow-up information; (3) the longest follow-up time was less than 180 days.

Abdominal CT was conducted before and after surgery (after consent from patients), and an axial periumbilical image at the L3 vertebra (approximately the level of the umbilicus) was scanned and saved. ImageJ software (National Institutes of Health, Bethesda, MD) was then used to measure related abdominal data, including the width of the linea alba, the total width and thickness of the rectus muscle, the flatness (flatness = thickness/total width) and cross-sectional area of the rectus muscle, and the circumference of the abdominal cavity (ie, intra-abdominal circumference). Calibration of body shape variation (correction value) was calculated as total width divided by intra-abdominal circumference. Clinical characteristics—age, BMI, number of pregnancies, etc—were collected. In addition, related postoperative complications were recorded, and patient satisfaction with abdominal contour was evaluated with a 5-point Likert scale (1, not at all satisfied; 2, not satisfied; 3, general; 4, satisfied; 5, completely satisfied). Satisfaction was calculated by the following formula: (number of 5-point scores) + (number of 4-point scores)/overall number of patients × 100%.

Statistical Analysis

Statistical methods included one-way analysis of variance (ANOVA), paired t-test, and Wilcoxon rank-sum test, with P < .05 being considered as statistical significance. All statistical procedures were conducted with SPSS, v. 25.0 (IBM).

Operative Technique

Double Folds of the Rectus Abdominis

Following the completion of the abdominal wall flap dissection, methylene blue was applied to delineate the medial border of the rectus abdominis muscle, corresponding to the outer edge of the linea alba (referred to as line 1). To facilitate the restoration of the rectus abdominis muscle to its prepregnancy condition as much as possible, it is recommended that a reinforcement line (designated as line 2) be drawn on the lateral side of line 1 (based on preoperative CT measurement data). When the mean width of the rectus abdominis muscle is less than 6 cm, the reinforcement line should be positioned 0.5 cm lateral to line 1. If the mean width of the rectus abdominis muscle is 6 cm or greater, the reinforcement line should be placed 1 cm lateral to line 1.

Suturing the First Layer

A continuous suture of line 1 with a No. 0 PDS loop (absorbable suture) was performed to tighten and align the medial border of the rectus abdominis. First, a continuous suture was started from the upper edge of the umbilical stalk to the unseparated part of the subxiphoid rectus abdominis, the rectus abdominis was then tightened, and the knots were buried deep. In the same manner, a continuous suture on line 1 was placed inferiorly from the lower edge of the umbilical stalk to the unseparated site of the rectus abdominis on the pubic symphysis.

Suturing the Second Layer

An interrupted suture with No. 2 nonabsorbable suture was used to tighten line 2 on both sides (3-4 stitches above/below navel). All sutures were tightened and the knots were buried deep. In this way, a hole with a diameter of about 1.5 to 2 cm was preserved at the umbilicus for the passage of the umbilical stalk, while also maintaining a deep position of the umbilical stalk and facilitating remodeling of the abdominal contour. See Video for details.

RESULTS

In total, 400 eligible women were recruited in this study, including 171 nulliparae (mean [standard deviation] age, 25.510 [3.913] years). Postpartum abdominoplasty was performed in 229 women: 106 (mean age, 33.280 [6.201] years) after 1 pregnancy (Group 1) and 123 (mean age, 33.350 [4.591] years) after 2 or more pregnancies (Group 2). The average patient follow-up time after abdominoplasty was 253.537 [66.276] days (range, 181-584 days). Significant differences were found among these 3 groups according to one-way ANOVA (P < .05), and therefore intergroup comparisons were also conducted.

The mean linea alba width was 11.102 [3.596] mm in the nulliparous group and this significantly increased to 27.569 [8.757] mm (P = .000) and 32.940 [10.111] mm (P = .000) in Groups 1 and 2, respectively. The total width of the rectus muscle significantly increased from 112.168 [14.483] mm in the nulliparous group to 119.455 [12.907] mm in Group 1 (P = .000), but did not further increase in Group 2 (118.779 [11.890] mm) (P = .702). After controlling for variation of somatotype, a similar trend was observed for the total width of the rectus muscle. No statistical difference was found in rectus muscle thickness between the nulliparous group (10.697 [1.593] mm) and Group 1 (10.334 [1.644] mm), but the thickness significantly reduced to 9.710 [1.964] mm in Group 2 (P = .007). However, as the number of subsequent pregnancies increased, the flatness of the rectus abdominis muscle continued to decrease, ie, the rectus abdominis muscle became flatter. In terms of the cross-sectional area of the rectus muscle, no significant difference was reported between the nulliparous group (950.556 [177.812] mm2) and Group 1 (942.320 [176.321] mm2) (P = .714), but there was a remarkable reduction in Group 2 (870.033 [190.752] mm2) (P = .003). See Table 1 for details.

Table 1.

Comparison of the Patient Groups by One-Way ANOVA with LSD or Tamhane's T2 Test^a

	Nulliparous group (n = 171)	Group 1 (n = 106)		Group 2 (n = 123)
	Mean [SD]	Mean [SD]	P	Mean [SD]	P
Age (years)	25.510 [3.913]	33.280 [6.201]	—	33.350 [4.591]	—
BMI (kg/m2)	20.587 [2.884]	20.479 [2.303]†	.981	20.369 [2.038]†	.974
Linea alba width (mm)	11.102 [3.596]	27.569 [8.757]**	.000	32.940 [10.111]**	.000
Total width of rectus (mm)	112.168 [14.483]	119.455 [12.907]**	.000	118.779 [11.890]†	.702
Thickness of rectus (mm)	10.697 [1.593]	10.334 [1.644]†	.090	9.710 [1.964]**	.007
Flatness of rectus	0.193 [0.037]	0.175 [0.033]**	.000	0.164 [0.035]*	.029
Rectus cross-sectional area (mm2)	950.556 [177.812]	942.320 [176.321]†	.714	870.033 [190.752]**	.003
Total rectus width-to-circumference ratio	0.198 [0.020]	0.205 [0.021]**	.006	0.201 [0.019]†	.189

ANOVA, analysis of variance; LSD, least significant difference; SD, standard deviation. ^aSignificant differences were found among the 3 groups according to one-way ANOVA (P < .05), and therefore inter-group comparisons were further conducted (LSD or Tamhane's T² test). The P values compare each group to the previous: Group 1 vs nulliparous, Group 2 vs Group 1: *P＜.05; **P＜.01; ^†P＞.05.

As shown in Table 2, patient satisfaction with abdominal contour significantly improved after postpartum abdominoplasty from 14.8% to 88.7%. In addition, no severe complications were observed, such as hematoma, RD recurrence, and linea alba hernia. Postoperative CT examination was carried out in 32 patients during the follow-up period (Group 3). Compared with preoperative data, the postoperative linea alba width was reduced from 32.018 [10.666] mm to 4.669 [3.033] mm (P = .000); the total width of the rectus muscle was reduced from 120.000 [16.131] mm to 110.653 [13.822] mm (P = .000), but its flatness increased from 0.159 [0.030] to 0.205 [0.032] (P = .000), its thickness increased from 9.404 [1.252] mm to 11.244 [1.670] mm (P = .000), and its cross-sectional area increased from 906.999 [114.940] mm² to 933.903 [123.317] mm² (P = .001). It is worth noting that after controlling for variation of somatotype, a similar trend was observed in the width of the rectus muscle. See Table 3 for details.

Table 2.

Evaluation of Patient Satisfaction

Group	5-point Likert scale					Z	P
	5	4	3	2	1
Preoperative	0 (0.0)	34 (14.8)	8 (3.5)	63 (27.5)	124 (54.1)	−12.668	.000
Postoperative	117 (51.1)	86 (37.6)	19 (8.3)	7 (3.1)	0 (0.0)

5-point Likert scale: 1, not at all satisfied; 2, not satisfied; 3, general; 4, satisfied; 5, completely satisfied. Values are n (%). Statistical analysis was performed with a Wilcoxon rank-sum test.

Table 3.

Preoperative and Postoperative Comparisons

	Preoperative	Postoperative	P
Linea alba width (mm)	32.018 [10.666]	4.669 [3.033]	.000
Total width of rectus (mm)	120.000 [16.131]	110.653 [13.822]	.000
Thickness of rectus (mm)	9.404 [1.252]	11.244 [1.670]	.000
Flatness of rectus	0.159 [0.030]	0.205 [0.032]	.000
Rectus cross-sectional area (mm2)	906.999 [114.940]	933.903 [123.317]	.001
Total rectus width-to-circumference ratio	0.207 [0.024]	0.198 [0.021]	.000

Values are mean [standard deviation].

DISCUSSION

The rectus abdominis, as the primary muscle of the anterior trunk, plays a crucial role in spinal flexion, respiratory assistance, protection of abdominal organs, and maintenance of intra-abdominal pressure. However, alterations in its structure can significantly impact both its contour and function. Postpregnancy hormonal changes and fetal growth often lead to increased abdominal pressure, which subsequently modifies the morphology of the rectus abdominis muscle.¹ This is primarily manifested as RD, characterized by the widening and flattening of the muscle, thereby affecting abdominal contouring. Current primary interventions for addressing RD and morphological alterations are categorized into 2 types: nonsurgical and surgical. Nonsurgical approaches, including exercise, physical therapy, and electrical stimulation,^3,4 have demonstrated some efficacy in mild cases of RD but are less effective in severe cases and lack substantial high-grade evidence from research studies.^5,6 Consequently, surgical intervention remains particularly important. Procedures such as abdominoplasty and rectus abdominis plication not only address diastasis but also repair hernias, restore function, and alleviate pain and other discomforts.^7-9

The findings of our study generally align with existing literature;¹⁰ however, some discrepancies were observed. First, the widening of the linea alba (ie, RD) was found to be more pronounced with an increasing number of pregnancies. Notably, the width of the rectus abdominis muscle increased in Group 1 but did not continue to expand in Group 2, a trend that persisted even after adjusting for variations by applying corrected values. Second, the thickness of the rectus muscle did not significantly decrease in Group 1, whereas a significant reduction was observed in Group 2, resulting in a flatter rectus abdominis muscle. Third, the cross-sectional area of the rectus muscle progressively diminished with the number of pregnancies, further illustrating the morphological changes postpregnancy, characterized by a reduced total volume. Consequently, the restoration of the rectus abdominis muscle to its preoperative state is a shared objective for both plastic surgeons and patients. The plication of the rectus abdominis remains a widely accepted approach for repairing RD. Although current procedures are still largely based on Pitanguy's study, substantial variations have been reported concerning hernia repair methods, suture selection, and the number of layers involved.¹¹ A previous study on severe RD suggested the incorporation of mesh in hernia repair, as rectus abdominis plication alone may result in a high recurrence rate of RD.¹⁰ Conversely, another study reported no recurrence following abdominoplasty in RD patients with abdominal hernia.¹² Some researchers¹³ have highlighted that the efficacy of rectus abdominis plication is not contingent upon the use of absorbable¹⁴ vs nonabsorbable sutures,¹⁵ aligning with findings from another study that demonstrated favorable long-term outcomes with both absorbable and nonabsorbable sutures. Through comprehensive clinical observation, we have identified specific limitations associated with the exclusive use of either absorbable or nonabsorbable sutures. Consequently, we propose the suture technique detailed in this article, which offers 2 distinct advantages. First, the use of continuous sutures with absorbable materials in the deep layer ensures that, even if the knot becomes inadvertently loosened, the intermittent sutures with nonabsorbable materials continue to provide lateral support, thereby preventing any overall relaxation of the tightened rectus abdominis muscle. Second, the PDS suture material employed for deep continuous sutures is relatively rigid, potentially causing a pronounced foreign body sensation in patients with minimal subcutaneous abdominal wall fat. In contrast, nonabsorbable polyester sutures are softer, and the absorbable sutures can be effectively embedded in the deeper layers.

Based on our clinical experience, we adopted the following repair strategy. (1) We do not utilize meshes. (2) We implement a layered suturing technique, in which we apply a continuous suture in the initial layer to approximate the separated rectus abdominis muscle, followed by a second layer of interrupted sutures to reinforce the repair. The placement of the reinforcing sutures was guided by preoperative CT measurements of the rectus abdominis muscle width. (3) Our suture selection criteria involves the use of absorbable sutures for the first layer and nonabsorbable sutures for the second layer. This suturing technique eliminates the need for mesh application and effectively addresses the separation of the rectus abdominis. The application of a secondary layer of nonabsorbable sutures not only enhances the durability of the repair and restores the rectus abdominis muscle to its prepregnancy condition but also prevents rupture of the initial continuous suture layer. Additionally, patient satisfaction with the abdominal contour was significantly improved. Postoperative follow-up proved that the effect was stable, without serious complications such as abdominal hernia, recurrence of RD, etc. Therefore, our suture pattern is reliable and worthy of promotion and application. See Figures 1-3 for details.

Figure 1.

A 34-year-old woman following 2 pregnancies. Surgical treatment was sought because of abdominal skin laxity and abdominal linea alba width. Preoperative CT revealed a 28-mm separation of the rectus abdominis muscle. We performed the double-fold repair described in this study for rectus abdominis muscle separation. During the operation, 300 mL of liposuction was performed, and 0.4 kg of excess abdominal flap was removed. Twelve months after surgery, we observed that the rectus abdominis muscle morphology was still well preserved without significant separation. The abdomen is naturally contoured. The patient was very satisfied with the surgical results. (A) Preoperative CT, and photographs of (B) anterior, (C) mid lateral, (D) flexion 45° lateral, and (E) lateral views, demonstrating the extent of linea alba width, skin laxity, and tissue excess, both centrally and laterally. (F) Postoperative CT, and photographs of (G) anterior, (H) midlateral, (I) flexion 45° lateral, and (J) lateral views at 12 months, demonstrating the power of the abdominoplasty technique to address linea alba, skin, and tissue excess. CT, computed tomography.

Figure 3.

A 29-year-old woman following 2 pregnancies. Surgical treatment was sought because of abdominal skin laxity and abdominal linea alba width. Preoperative CT revealed a 41-mm separation of the rectus abdominis muscle. We performed the double-fold repair described in this study for rectus abdominis muscle separation. During the operation, 450 mL of liposuction was performed, and 0.7 kg of excess abdominal flap was removed. Ten months after surgery, we observed that the rectus abdominis muscle morphology was still well preserved without significant separation. The abdomen is naturally contoured. The patient was very satisfied with the surgical results. (A) Preoperative CT, and photographs of (B) anterior, (C) midlateral, (D) flexion 45° lateral, and (E) lateral views, demonstrating the extent of linea alba width, skin laxity, and tissue excess, both centrally and laterally. (F) Postoperative CT, and photographs of (G) anterior, (H) midlateral, (I) flexion 45° lateral, and (J) lateral views at 10 months, demonstrating the power of the abdominoplasty technique to address linea alba, skin, and tissue excess. CT, computed tomography.

Figure 2.

A 35-year-old woman following 2 pregnancies. Surgical treatment was sought because of abdominal skin laxity and abdominal linea alba width. Preoperative CT revealed a 29-mm separation of the rectus abdominis muscle. We performed the double-fold repair described in this study for rectus abdominis muscle separation. During the operation, 500 mL of liposuction was performed, and 0.4 kg of excess abdominal flap was removed. Fifteen months after surgery, we observed that the rectus abdominis muscle morphology was still well preserved without significant separation. The abdomen is naturally contoured. The patient was very satisfied with the surgical results. (A) Preoperative CT, and photographs of (B) anterior, (C) midlateral, (D) flexion 45° lateral, and (E) lateral views, demonstrating the extent of linea alba width, skin laxity, and tissue excess, both centrally and laterally. (F) Postoperative CT, and photographs of (G) anterior, (H) midlateral, (I) flexion 45° lateral, and (J) lateral views at 15 months, demonstrating the power of the abdominoplasty technique to address linea alba, skin, and tissue excess. CT, computed tomography.

Following abdominoplasty involving double folds of the rectus abdominis, we observed a significant narrowing of the linea alba, a reduction in the width of the rectus muscle, and an increase in its thickness, indicating a correction of the previous flattening. Additionally, the postoperative cross-sectional area of the rectus muscle was significantly larger, and its volume was restored compared with presurgical measurements. We hypothesize that these changes may be related to the morphological alterations and RD that occur postpregnancy, which can lead to rectus muscle dysfunction and mild atrophy. Postsurgical correction appears to facilitate the gradual recovery of rectus muscle function and an increase in muscle size. Although our study highlights these morphological changes, there remains a paucity of research on the functional alterations of the rectus muscle postsurgery.

Rectus diastasis and flattening are common occurrences following pregnancy and can be effectively addressed through abdominoplasty, which demonstrates a stable clinical effect and high patient satisfaction. This suggests that abdominoplasty is a reliable treatment option worthy of broader adoption and application. Furthermore, it provides a clinical foundation for enhancing surgical techniques in rectus muscle repair. However, this study has several limitations. First, we focused solely on the morphological changes of the rectus muscle before and after pregnancy and abdominoplasty, without assessing its functional aspects. Second, the limited duration of follow-up prevented us from evaluating the long-term stability of the surgical outcomes, particularly in patients who become pregnant again. Finally, due to the variability among postoperative patients, we were unable to collect sufficient postoperative CT data for comparison with preoperative data, an issue that needs to be addressed in future research.

CONCLUSIONS

Pregnancy can lead to diastasis of the rectus abdominis muscle, characterized by morphological alterations such as the widening of the linea alba and the widening and flattening of the rectus abdominis muscle. Through the implementation of a double-fold repair technique for the rectus abdominis muscle, the muscle's tension is effectively restored to its prepregnancy condition. The surgical outcomes are stable, and postoperative patient satisfaction is notably high.

Disclosures

The authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.

Funding

The authors received no financial support for the research, authorship, and publication of this article.