Amniotic fluid protects the fetus, reflects the fetal condition, and provides an environment for various fetal movements, including breathing [1,2]. Oligohydramnios is associated with maternal and fetal hypertension, diabetes, congenital anomalies, fetal growth restriction, and preterm rupture of membranes. Independently, it has been reported to reflect uteroplacental insufficiency and chronic fetal hypoxia [3,4]. When oligohydramnios is diagnosed by chance during the routine second and third trimester pregnancy examination, clinicians tend to recommend a variety of tests to identify its causes, such as the presence of congenital malformations and the size of the fetus, and to conduct fetal surveillance including Doppler studies.

Oligohydramnios without any evidence of either maternal or fetal abnormalities is known as “isolated” oligohydramnios (IO) [5]. In low-risk pregnancies, the incidence of IO has been estimated as 1.5% [6]. IO management guidelines are not well defined as its effect on perinatal outcomes remains controversial. However, a recent meta-analysis has suggested that IO in low-risk pregnancy was associated with adverse outcomes such as neonatal intensive care unit (NICU) admission, cesarean delivery, and meconium aspiration syndrome [7]. A systematic review and meta-analysis suggested that oral or intravenous maternal hydration improves amniotic fluid volume; however, further evaluation of its clinical application is required [8].

Given the potentially severe complications and lack of clear management guidelines, the diagnosis of IO can affect pregnancy management and the decision to induce labor. In fact, a 2009 survey of Society for Maternal Fetal Medicine (SMFM) has revealed that approximately 80% of the participants declared either that induction of labor in cases of IO did not reduce perinatal morbidity or that they were uncertain whether it did. However, despite being unsure of its benefits, 96% of the practitioners leaned towards intervention [9].

In the absence of IO management guidelines, insights into obstetricians’ clinical practice patterns are required. This survey aimed to investigate the knowledge and clinical practice patterns associated with IO management among the members of the Korean Society of Maternal Fetal Medicine (KSMFM).

From December 2018 to February 2019, questionnaires were sent to 272 labor units listed by the Korean Statistical Information Services (KOSIS) as suitable labor premises. The institutes included 41 obstetrics departments within university hospitals, 86 obstetrics departments within general hospitals, and 145 private obstetric hospitals. The survey comprised of seven questions and was distributed by e-mail.

IO was defined as an ultrasonography-based diagnosis of abnormally low amniotic fluid with intact membranes in the absence of a fetal growth restriction, fetal anomalies, or significant maternal comorbidity. The participants were asked to report on their management of such cases, based on their personal and their unit’s standard protocols. The questionnaire was composed of three parts: 1) measurement and related perinatal outcomes of IO, 2) preferences for induction of labor in presence of IO atthird trimester and 3) preferences of oral or intravenous hydration and intraamniotic fluid infusion in IO. In this questionnaire-based survey, respondents were asked to provide details of their individual characteristics, such as medical practice setting, age, sex, and the year of their certification as obstetrical specialists. The questionnaire was adapted from an earlier survey for SMFM members regarding the same matter [9].

Amniotic fluid physiologic dynamics during pregnancy are complex. Abnormal volumes of amniotic fluid are associated with various adverse pregnancy outcomes [10]. Oligohydramnios is estimated to occur in 0.5–5.5% of all pregnancies, depending on the method of amniotic fluid volume measurement [11-13]. Oligohydramnios without any evidence of anatomical, functional, or chromosomal abnormalities is called “isolated” oligohydramnios. Since IO indicates a lowrisk pregnancy and the oligohydramnios measurements have a low accuracy, the IO management protocols are debatable [5,14].

In the present questionnaire-based survey, the majority of respondents used AFI to measure amniotic fluid volume. The gold standard for the amniotic fluid volume estimation is the dye dilution test [15]. However, this test is invasive, and is rarely required or used. Thus, single deepest pocket (SDP), measuring ≤2 cm, or AFI ≤5 cm are the commonly used indirect criteria for confirmation of oligohydramnios [16]. However, SDP and AFI often grossly under- or over-estimate oligohydramnios [17,18]. Although, neither of the two assessments have been proved to be superior to the other; when the AFI was used, significantly more cases of oligohydramnios were diagnosed, and more women underwent interventions [19].

Patients with oligohydramnios have high-risk pregnancies, associated with adverse outcomes such as admission to the NICU, meconium stained amniotic fluid, increased rate of cesarean section, low Apgar score at birth, fetus that is small for gestational age, low umbilical cord pH, and respiratory distress syndrome. However, since IO indicates a low-risk pregnancy, its evaluation as a risk factor for adverse pregnancy outcomes is still controversial [20]. In a recent meta-analysis of 12 studies, Shrem et al. [10] reported that IO at term was associated with significantly higher rates of labor induction, cesarean section, and short-term neonatal morbidity. Moreover, Rabie et al.[7] reported that IO in low-risk pregnancy increased the risk of NICU admission, cesarean delivery for fetal distress, and meconium aspiration syndrome. In the present survey, over 50% of the participants reported cesarean delivery, abnormal fetal heart rate, and meconium aspiration syndrome in neonates as adverse outcomes associated with IO. This was in accordance with the previous SMFM survey (Fig. 1). However, the proportion of the response of “no significant attributable risks” differed in the two surveys. This may be attributed to the increased understanding of IO in perinatal outcomes during the last 10 years.

Due to the associated adverse outcomes, interventions, such as labor induction, are important considerations when treating patients with confirmed IO in the third trimester of pregnancy. In 2009, the SMFM questionnaire-based survey revealed that approximately 80% of the participants believed that induction of labor in cases of IO did not reduce perinatal morbidity or that they were uncertain whether it did. However, despite being unsure of its benefits, 96% of the practitioners recommended this intervention [9]. Conversely, in the present survey, nearly 74% of the participants believed that induction of labor reduced perinatal morbidity and almost 70% of them indicated considering induction of labor in the third trimester of pregnancy with IO (Fig. 2). These results show that the perceptional uncertainty of labor induction for IO has reduced in the last 10 years. Furthermore, 68% of the participants declared that late pre-term to early-term period (36–38 gestational weeks) was a suitable timeframe for delivery. In a recent study, Rabies et al. have reported that the lack of required data precludes any conclusions regarding optimal timeframe for delivery in pregnancies with IO [7]. Conversely, Brzezinski-Sinai et al.[14] have reported that in cases of IO in late pre-term, induction of labor may reduce the risk of perinatal morbidities despite a premature birth. The American College of Obstetricians and Gynecologists (ACOG) recommendations state that 36.0–37.7 weeks of gestation are a suitable timeframe for delivery in cases with IO [21]. Given these considerations, until 35.6 weeks of gestation, conservative management is required. Further, until delivery, intensive fetal surveillances including fetal biophysical profile and Doppler analysis to evaluate placental dysfunction are needed [22,23]. In the KSMFM survey of 70 members in 2013, Oh reported that fetal surveillances were performed twice a week (20%), every week (43%) or every other week (35%), and 46% of respondents preferred induction after 37 gestational weeks in IO [24]. This result was similar to that of our survey.

Previous meta-analyses suggest that maternal hydration appeared to increase amniotic fluid volume and might be beneficial in the management of oligohydramnios [8,25]. In the SMFM survey, 51% of respondents thought that hydration (oral or intravenous) should be performed to gain additional amniotic fluid [9]. In the present survey, 47% of the participants believed that hydration had an effect in conservative management of IO. Based on this result, maternal hydration may be considered in clinical practices for IO management. Concurrently, majority of the survey participants (87.5%) declared that they did not consider amnioinfusion as a necessary practice in IO management.

This study had some limitations, including a low response rate, which was probably due to a reduced number of obstetricians in the Korean Society. The low response rate might have introduced different kinds of bias to the findings. Further, this survey showed results similar to the previous KSMFM survey of 2013 regarding the preferred induction time [24]. However, we believe that several additional questions including perception of hydration and perinatal outcomes are worth investigating than the previous study to understand additional clinical practice patterns. Additionally, 64% and 83% of participants worked for tertiary hospitals in this study and the previous study, respectively [24]. This suggests that this study represented the general practices in Korea. In conclusion, KSMFM members preferred inducing labor at late-preterm to early-term, to decrease perinatal morbidity in cases of IO, in accordance with the recent ACOG recommendation, although it is still uncertain whether labor induction improves the outcomes. Future prospective studies are needed regarding IO management.