Comparison of postpartum sonographic findings after uneventful vaginal and cesarean section deliveries

The puerperium is defined as the 6–8 week period following delivery. The uterus weighs more than 1 kg immediately after delivery, and then undergoes physiological involution and finally returns to the non-pregnant state. Normal puerperal changes may affect the sonographic view of the uterus. Early postpartum hemorrhage occurs in the first 24 hours after delivery⁽¹⁾. Ultrasound (USG) plays a vital role in the diagnosis of early postpartum hemorrhage and also is the front line imaging examination in woman with suspected pelvic postpartum complications both following vaginal delivery or cesarean section^(2–4). Thus, the knowledge of normal postpartum sonographic findings after vaginal delivery and cesarean section is very important to avoid misdiagnosis and inappropriate treatment. Late postpartum hemorrhage is defined as bleeding after the first 24 hours following delivery. Placental and fetal membrane residuals are well known causes of late postpartum hemorrhage⁽⁵⁾, and placental residue associated endometritis may also cause significant bleeding in this period.

In the current study, we have investigated the sonographic findings of the uterus and pelvis after uneventful vaginal delivery and cesarean section, 24 hours after delivery.

This prospective observational study was conducted between July 2015 and May 2018 in a tertiary center, Trakya University, Faculty of Medicine, Department of Perinatology. Data collection was approved by our Institutional Review Board.

Sonography

All scans were performed transabdominally by two experienced operators (I.C., H.S) using commercially available real time machines (Voluson 730 Expert/Voluson E6, General Electric, Tiefenbach, Austria) with a 4-to-8-mHz probe (RAB 6D). Ultrasound was performed 24 hours after delivery.

Mid-sagittal and/or axial planes of the uterus were used to measure the thickness of the anterior and posterior uterine walls, the endometrial thickness and the uterine width (Fig. 1, Fig. 2). The distance between the uterine fundus and promontorium and between the uterine fundus and L5 vertebra was also measured in the mid-sagittal plane of the uterus (Fig. 3). The mid-sagittal plane of the pelvis was also used to measure the length of the uterus, from the external os of the cervix to the fundus and the maximal pocket of fluid, if any, in the pelvic cavity. USG examination was feasible and the measurements were possible in all women.

Fig. 1.

Fig. 2.

Fig. 3.

Forty seven patients, with a mean (min–max) age of 26.5 (18–41) years, who had delivered at ≥37 weeks were prospectively included. Twenty women (42.5%) delivered vaginally, whereas 27 (57.4%) by cesarean section. The most common indication for cesarean section was repeat cesarean section (n = 19). Other indications included breech presentation (n = 3), macrosomia (n = 1), dystocia (n = 2) and non-reassuring fetal cardiotocography (n = 1). Sixteen women (34%) were primiparous and 31 (65.9%) were multiparous. Demographic characteristics, mean gestational age at delivery, parity and birth weight were similar in the groups (Tab. 1).

The distance between uterine fundus and cervix was significantly higher in the vaginal delivery group compared to the cesarean section group (184.05 ± 16.8 vs 163.6 ± 6.7 mm, p <0.001). The measurements of anterior and anterior-posterior walls of the uterus, anteroposterior uterine length and uterine width were similar in the groups (Tab. 1). Promontorium-fundus length was significantly higher in patients who delivered vaginally vs cesarean section (123.3 ± 13.6 – 108.7 ± 23.3 mm, p = 0.005). L5-fundus length was also greater in the vaginal delivery group (92.7 ± 15.3 – 85.1 ± 14.3 mm), but this difference did not reach the significance level.

There was a significant correlation between fundus-cervix length and L5-fundus length (r = 0.304, p <0.05). The distance between the uterine fundus and L5 was also significantly correlated with endometrial thickness, posterior wall of the uterus, promontorium-fundus length and anteroposterior length of the uterus (Tab. 2).

The mean (min–max) endometrial thickness in the vaginal delivery and cesarean section groups was 13.3 (4–25) and 12.4 (4–29) mm, respectively. Three (11.1%) patients in the cesarean section group and two (10%) in the vaginal delivery group had coagulum-like mass which was smaller than 3 cm in (anteroposterior) length in the cervix. None of these patients experienced abnormal vaginal bleeding during the hospitalization or the puerperal phase. Minimal, transient pelvic effusion with a maximum depth of 1cm was observed in the pouch of Douglas in three (11.1%) patients after cesarean section. No fluid was visualized in the abdomen or the pelvis in women who had vaginal delivery. There was a significant correlation between parity and uterine width (r = 0.304, p <0.05) (Tab. 2).

In this study, we have described normal abdominal and pelvic USG images 24 hours following cesarean section and vaginal delivery, in the postpartum period. We have observed minimal transient pelvic effusion in three (11.1%) patients who had uneventful cesarean deliveries. Antonelli et al. ⁽⁶⁾ found free-fluid effusion in only two out of 145 women (1.4%) four days following cesarean section, but in another study, no free fluid was observed within 24 hours following uneventful cesarean delivery⁽⁷⁾. We believe that free fluid collection except for minimal fluid accumulation in the pouch of Douglas should be considered as an abnormal finding after delivery.

We have found that the promontorium-fundus length and the fundus-cervix length were significantly greater in patients with vaginal delivery compared to those who had cesarean section. We have found non-significantly greater uterine width and L5-fundus lengths in the vaginal delivery group. A larger uterine size was observed in patients who had vaginal delivery compared to those who had cesarean section. Lousquy et al. ⁽⁸⁾ have also found that uterine length was significantly greater in patients who delivered by vaginal route vs cesarean section. They believe that this results from different oxytocin doses (15 vs 55 units). In our study, the total doses of oxytocin administered during delivery and early postpartum period were 35 and 45 units, respectively. Uterine measurements were performed at 24 hours after delivery and none of the patients received oxytocin during the last 12 hours. Therefore, our findings could not be attributed to oxytocin usage.

In another study, significantly greater uterine lengths were reported following cesarean section vs vaginal delivery (22.5 vs 17.3 cm). It has been hypothesized that the uterus contracts more efficiently and stays firmer after vaginal delivery than after cesarean section⁽⁹⁾. We can think that larger uterine dimensions following vaginal delivery might be explained by the labor itself and be a completely normal finding, but it may also be a sign of poorly contractile uterus in symptomatic patients. Therefore, uterine length measurement seems to be an important part of postpartum sonographic evaluation.

In our study, we have found a significant correlation between fundus-cervix and L5-fundus distances (r = 0.304, p <0.05). There was also a strong positive correlation between L5-fundus and promontorium-fundus measurements (r = 0.632, p <0.01).

The measurement of uterine length from the fundus requires significant pressure on the uterus, which is difficult to perform in patients after cesarean delivery due to the postoperative pain. Measuring the distance between the L5 vertebra and the uterine fundus seems to be more informative and is less painful. In cases where L5-fn measurement is not possible, Pr-fn measurement is also a reasonable option.

On the other hand, no difference in endometrial thickness was found between women who had cesarean section and those after vaginal delivery. The mean endometrial thickness was 13.3 (4–25) mm for vaginal delivery and 12.4 (4–29) mm for cesarean section. We can conclude that homogenous endometrial thickness up to 30 mm at 24 hours after vaginal and cesarean delivery can be accepted as a normal finding in the absence of abnormal bleeding. Moreover, a <30 mm coagulum-like structure in the cervical region may also be a normal finding. We have observed a coagulum-like image smaller than 3 cm in the anteroposterior direction in three (11.1%) patients after cesarean section and two (10%) patients in the vaginal delivery group. It has also been reported that an echogenic material can be present within the uterine cavity in up to 40% of asymptomatic women 48 hours following vaginal delivery⁽¹⁰⁾. Several authors have described routine ultrasound findings of the uterus following delivery^(10–13). Some reported sonographic findings after vaginal delivery while others after cesarean section. Also, the time-points of sonographic examinations were heterogeneous. Sokol et al. ⁽¹⁰⁾ performed USG examination within 48 hours following vaginal delivery while other authors reported sonographic findings seven days after vaginal delivery⁽¹³⁾. Since the majority of postpartum hemorrhages occur in the early postpartum period, we have performed ultrasound scans 24 hours following delivery. Sonographic evaluation of the uterus and pelvis may also play a very important role in the management of patients with an unexplained drop in hemoglobin levels after delivery without significant vaginal bleeding. Thus, knowledge on the normal appearance of the uterus following childbirth seems quite important for radiologists and clinicians to avoid misdiagnosis. Most studies on sonographic assessment of postpartum uterus did not provide uterine dimensions. Koskas et al. ⁽⁷⁾ evaluated uterine ultrasonographic findings after uneventful cesarean sections 24 hours following delivery; they measured some uterine dimensions in different planes. In other studies, uterine volumes were obtained, but uterine dimensions were not reported⁽¹³⁾. In our study, we have not only measured the uterine lengths in different planes, but we also reported some additional uterine distances, such as the L5-fundus and promontorium-fundus lengths. Additionally, we compared these results in women who delivered by vaginal and abdominal route.

Our study showed that homogenous endometrial thickness <30 mm may be a normal finding after delivery. Likewise, a coagulum-like mass up to 30 mm in the cervix may also be a normal finding in asymptomatic women. The measurement of L5-fundus distance is a simple and an effective technique to evaluate the size of the uterus. It may be employed instead of a fundus-cervix measurement and other uterine dimensions. Knowledge on the normal sonographic appearance of the postpartum uterus can help clinicians define the pathologic conditions and avoid misdiagnosis and overtreatment.