At present, the definition of preterm birth is still controversial. Flenady et al[17]. pointed out that any childbirth within gestational age between 20 and 36 weeks could be defined as Preterm birth which was the main contritbutor of perinatal morbidity and the second leading cause of neonatal death in the world. The most common clinical symptom of urolithiasis during pregnancy was renal colic and mainly was observed after 20 weeks of gestation[18]. In consideration of ritodrine hydrochloride’s indications (only for pregnant women after 20 gestational weeks) and the difficulty for monitoring uterine contractions at early gestation[19], thereby we only retrospective analyzed pregnant women at 20 to 36 gestational weeks. Johnson et al[12]. had shown that the obstetric complications after ureteroscopy were about 4.0%, but in our study there was nothing severe complication except for that 45.5% of patients developed to continuously regular contractions after ureteroscopy. The incidence of uterine contraction in our study was higher than that reported by other scholars[20]. The possible explanation were as follows: (1) All cases summarized in the study were patients with severe renal colic which could not be relieved by painkiller in outpatient department. In view of the relevance between pain and uterine contraction, the incidence of such complication rose accordingly. (2) All patients were received uterine contraction monitoring by EHG for 12 hours after surgery, thus any slight contractions could be detected in time and analyzed in the study, but in fact, some uterine contractions in early stage could disappear without any medical treatment. There was not any severe complications such as abortion or premature delivery happened in this study, the results suggest that ureteroscopy was a safe and effective surgical method and routine monitoring of uterine contractions after ureteroscopy might help to avoid pregnancy complications.
Compared with primipara, the cervix of multipara is easier to expand, which means a sooner labor process[21, 22]. Uterine contraction is stronger for multipara during labor and more analgesics are needed for painless delivery[23]. Our study showed that multipara were more likely to develop to uterine contraction after ureteroscopy. The possible explanations for this results were as follows: (1) Compared with primipara, the oxytocin receptor which played a key role in uterine contraction had a higher expression on uterus in multipara[24, 25]; (2) With the increasing of age, the incidence of pregnancy complications rose in step, multipara was more likely to develop to uterine contraction after operation[26, 27].
Enlarged uterus due to pregnancy inevitably result in ureter compression because of the adjacent location between lower segment ureter and cervix[28–30]. The operation of ureteroscope would inevitably stimulate the cervix, and repeatedly physical stimulation could trigger uterine contraction. Scholars had shown that pregnancy complications were prone to occur after long-time surgery[31], and shortening operation time could reduce such complications[32]. Our results also indicated that operation time was a risk factor for uterine contraction. This study showed that each additional a quarter increase, the adjusted odds ratio was as high as 2.385. This result also reminded that the surgeons should shorten operation time as much as possible when ureteroscopies are performed on pregnant women. The purpose of ureteroscopy was just to resolve urethral obstruction, not for removing stones.
Phloroglucinol, as a non-papaverine antispasmodic, only acts on spastic smooth muscles and has minimal impact on normal smooth muscles. Application of phloroglucinol during pregnancy does not increase the risk of fetal malformations[33]. It was applied to relieve renal colic and inhibit uterine contractions for decades[34, 35]. Our research showed that application of phloroglucinol after ureteroscopy could reduce the incidence of uterine contractions. In this study, only a few doctors prescribed phloroglucinol to patients after ureteroscopy. In view of the effectiveness and safety of this medication, we suggested that such drug could be applied to more patients.
If severe pain persists, human body would release prostaglandins which could promote cervical ripening and lead to smooth muscle contraction in uterine[36, 37]. Pain could also cause stress response and then trigger a increasing release of catecholamines that plays an important role in uterine contractions[38]. Furthermore, severe renal colic often accompanies with repeated vomit which may lead to uterus compression. Mechanical stimulation could also induces uterus contractions[39]. Our research also showed that unrelieved pain after surgery was a risk factor for uterine contractions. About a quarter of the patients in this study had little relieve in renal colic immediately after ureteroscopy. The result was coincide with other scholars[3]. The possible explanations was that the double J catheter inserted into ureter during operation did not play a effective role in drainage soon after surgery. With painkiller prescribed, pain in these patients gradually subsided in 12 hours after operation.
During the operation of ureteroscopy, continuously intraureteral perfusion by saline is required. Increasing water pressure in ureter would force bacteria flow back into blood via renal pelvic-vein system, it is more likely to happen in patients with urinary tract infection. Bacteremia may result in spread of inflammation or even progress to SIRS which could develop to multiple organ dysfunction syndrome(MODS)[40]. Inflammatory mediators would be release and spread if SIRS occurs, such mediators could lead to uterus contraction[41, 42]. Our research also suggested that SIRS was a risk factor for uterus contraction. Pregnant women were more likely to develop to sepsis due to immunosuppression and down regulation of inflammatory response because of immunotolerance in pregnancy[43]. pregnant women with SIRS or sepsis may easily be ignored because of unconspicuous fever and quick heart rate caused by ritodrine hydrochloride[44], therefore, it is necessary to closely monitor the infection indicators, such as white blood cells, CRP, and PCT-Q and so on, in order to find potential infection in time.