Effect of oral hydration therapy on amniotic fluid index and maternal-neonatal outcomes in pregnant women with oligohydramnios: a systematic review and meta-analysis

Introduction

Amniotic fluid is vital for foetal growth, providing cushioning, enabling movement, and supporting lung and musculoskeletal development. It is assessed via ultrasonography using the amniotic fluid index (AFI), with oligohydramnios defined as an AFI below 8 cm or a single deepest vertical pocket (SDVP) under 2 cm [1], 2]. Affecting approximately 0.5–5 % of gestations, this condition is linked to increased maternal and neonatal risks, including foetal growth restriction, umbilical cord compression, meconium aspiration syndrome, preterm birth, and higher rates of operative delivery, such as caesarean section [3]. Beyond perinatal risks, reduced amniotic fluid may limit foetal movement, leading to musculoskeletal abnormalities, and increase umbilical cord compression, causing hypoxia and foetal distress. Early detection and management are essential to improving maternal and neonatal outcomes [4].

Maternal oral hydration therapy has emerged as a promising, non-invasive intervention for oligohydramnios. Research has shown that both oral and intravenous hydration therapy can enhance amniotic fluid levels, increase uteroplacental perfusion, and support foetal well-being [5], 6]. Oral hydration therapy stands out as an accessible, low-cost strategy, especially beneficial in resource-constrained settings where advanced medical interventions such as amnioinfusion may not be feasible [7]. Its physiological benefits are attributed to increased maternal plasma volume, improved uteroplacental blood flow, and augmented foetal urine production, the latter being a key determinant of amniotic fluid volume [8].

Clinical trials have highlighted the rapid and sustained effects of oral hydration on amniotic fluid levels, with improvements often observed within hours and lasting for several days [9], 10]. These studies have also reported favorable perinatal outcomes, such as reduced incidences of fetal distress, improved Apgar scores, and decreased neonatal intensive care unit (NICU) admissions [11]. Additionally, the simplicity and safety profile of oral hydration therapy make it an attractive option for outpatient management, potentially reducing the need for costly hospitalizations and invasive procedures.

Despite these promising findings, several limitations in the current literature warrant attention. Inconsistencies in the reported efficacy and variability in hydration protocols remain significant challenges. While some research suggests that isotonic or hypotonic fluids may offer superior benefits compared to plain water, no consensus exists on the optimal type, volume, or frequency of fluid intake [2], 12]. Another notable limitation is the predominant focus on third-trimester oligohydramnios. There is a lack of data on the use of hydration therapy in earlier stages of pregnancy, where intervention may yield different outcomes, or in pregnancies complicated by additional maternal conditions such as preeclampsia, gestational diabetes, or chronic hypertension. This systematic review and meta-analysis (SRMA) seeks to bridge these gaps by compiling the available evidence on oral hydration therapy in increasing amniotic fluid levels and enhancing maternal–neonatal outcomes in pregnancies affected by oligohydramnios.

Methods

This SRMA adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) 2020 guidelines [13] (Supplementary Table S1). We carried out a SRMA of randomized controlled trials, quasi-experimental studies and analytical observational studies. In addition, the study protocol was prospectively registered in the International Prospective Register of Systematic Reviews (Registration No. CRD42024617122).

Results

Study selection

A total of 231 studies were identified across five databases. After removing 124 duplicates, 107 studies remained for screening. Of these, 84 were excluded due to incorrect population (n=36), intervention (n=39), outcomes (n=2), study design (n=6), and lack of abstracts (n=1). Following full-text screening, 12 studies met the inclusion criteria for systematic review, with four included in the meta-analysis (Figure 1).

Figure 1:

PRISMA flowchart for study selection process.

Study characteristics

The individual study demographics are given in Table 1. This review included 12 studies: 8 RCTs, 2 NRCTs, 1 case-control, and 1 prospective interventional study from India, Italy, Japan, Iran, Pakistan, Iraq, and Georgia, with sample sizes of 10–200 participants. Mean maternal age ranged from 22.9 to 33.62 years in the intervention group and 23.4–31 years in controls. Primary maternal outcomes included AFI (measured from 1 h to 4 weeks), mode of delivery, hemoglobin concentration, and urine specific gravity. Neonatal outcomes assessed birth weight, APGAR scores, NICU admissions, perinatal death, and ventilatory support.

Table 1:

Baseline characteristics of studies included.

Author, year	Country	No. of patients		Mean age, years		Outcomes
		E	C	E	C
Randomized controlled trials
Doi et al. (1998) [9]	Japan	21	21	29.3	28.6	Maternal: AFI at 1 h, plasma osmolality, serum sodium level, hematocrit, Hb concentration
Lorzadeh et al. (2008) [22]	Iran	20	20	25.25 ± 4.27	24.9 ± 5.73	Maternal: AFI at 1 h, change in AFI
Singh et al. (2022) [23])	India	25	25	26.44 ± 3.37	24.88 ± 2.55	Maternal: AFI at 2 and 24 h, 7 days, mode of delivery Neonatal: birth weight, APGAR at 1 and 5 min
Salvi et al. (2022)a [12]	India	20		22.9		Maternal: AFI at 4 and 48 h, mode of delivery
Patil et al. (2018)a [24]	India	36		22.9 ± 4.1		Maternal: AFI at 2 and 24 h, mode of delivery, liquor colour Neonatal: NICU admissions and APGAR at 1 and 5 min
Deka et al. (2001)a [1]	India	25		Not mentioned		Maternal: AFI at 3 h, urine specific gravity
Malik et al. (2021)a [25]	Pakistan	50		33.62 ± 5.45		Maternal: AFI pre and post hydration (time not mentioned)
Patrelli et al. (2012)a [8]	Italy	66		26.1 ± 6.0		Maternal: AFI at 7 days, type of delivery Fetal: fetal birthweight, APGAR score, NICU admissions
Non-randomized controlled trials
Malhotra et al. (2004)a [7]	India	15		26.6 ± 3.2		Maternal: AFI at 3, 24, and 48 h
Flack et al. (1995) [26]	Georgia	10	10	31 (25–38) (median)	27 (23–34) (median)	Maternal: AFI at 2 h, plasma and urine osmolality, Doppler flow velocimetry (maternal and fetal)
Case-control study
Rashid et al. (2021) [10]	Pakistan	100	100	Not mentioned		Maternal: AFI at 1 h Fetal: birth weight, APGAR at 1 & 5 min, NICU admissions
Prospective interventional study (pre- post)
Chaudhary et al. (2022) [2]	India	75		25.96		Maternal: AFI at 2 h, 2 and 7 days, mode of delivery Neonatal: birthweight, APGAR at 1 and 5 min, NICU admissions, CPAP/ventilatory support

1. E, experimental; C, control; AFI, amniotic fluid index; NICU, neonatal intensive care unit; CPAP, continuous positive airway pressure. ^aThese studies were RCT/NRCT, but involved groups with different interventions and no control group or a control group with no oligohydramnios so were analysed as pre-post.

The pooled analysis of two RCTs [9], 22] assessing maternal oral hydration’s impact on AFI after 1 h included 41 participants per group (Table 2, Figure 2). The overall mean difference (MD) was 1.10 (95 % CI: −1.05 to 3.25) with high heterogeneity (I²=94.6 %, p<0.0001). The wide prediction interval (−22.59 to 24.79) indicates variability. Sensitivity analysis (Supplementary Figure S1) confirmed substantial heterogeneity, with Lorzadeh et al. [22], significantly influencing the pooled estimate (SMD: 1.10, 95 % CI: −1.05 to 3.25).

Table 2:

Pooled outcomes of studies.

Outcome	No. of studies	Pooled estimate mean difference 95 % CI	I2	Prediction interval	p-Value	Studies
Amniotic fluid index
AFI at 1 h	2	1.10 [−1.05 to 3.25]	94.6	−22.59 to 24.79	<0.0001	Doi et al. [9], Lorzadeh et al. [22]
AFI at 2 ha	2	0.996 [0.781–1.210]	0	–	0.000	Chaudhary et al. [2], Patil et al. [24]
AFI at 1 daya	2	0.853 [0.532–1.174]	0	–	0.000	Patil et al. [24], Malhotra et al. [7]
AFI at 2 daysa	3	1.649 [0.943–2.356]	75.384	−6.553 to 9.852	0.000	Malhotra et al. [7], Chaudhary et al. [2], Salvi et al. [12]
AFI at 1 weeka	3	2.232 [0.943–3.520]	95.843	−3.973 to 8.437	0.001	Chaudhary et al. [2], Malik et al. [25], Patrelli et al. [8]

1. AFI, amniotic fluid index; CI, confidence interval; I², heterogeneity statistic. ^aPre-post analysis was done for these outcomes in comprehensive meta-analysis software.

Figure 2:

Forest plot showing effect of material hydration on amniotic fluid index (AFI) after 1 h.

Discussion

This SRMA highlights the effectiveness of maternal oral hydration therapy in improving AFI in pregnancies complicated by oligohydramnios. The pooled results indicate statistically significant increases in AFI at multiple time points post-intervention, specifically at 2 h, 1 day, 2 days, and 1 week, suggesting that maternal hydration therapy is beneficial in enhancing amniotic fluid dynamics. Our findings align with previous studies that have established hydration therapy as a non-invasive, accessible, and cost-effective intervention for managing oligohydramnios.

The systematic review by Gizzo et al. [6] focused on maternal hydration strategies for improving AFI and concluded that oral hydration was superior to intravenous (IV) hydration, particularly with hypotonic fluids. Their meta-analysis found that AFI improvements were more time-dependent than dose-dependent, meaning that repeated hydration was necessary to maintain AFI increases. Our findings are consistent with this observation, as we also noted short-term increases in AFI, even within 2 h of hydration, reinforcing the idea that maternal hydration is an effective and immediate intervention. However, unlike Gizzo et al. [6], our review included a broader range of studies, demonstrating significant short-term and sustained AFI increases over a one-week period.

Another key takeaway from Gizzo et al. [6] was that IV hypotonic solutions produced greater AFI increases compared to isotonic IV fluids. The present meta-analysis also supports that consumption of hypotonic fluids such as plain water, can lead to rapid and significant increase in AFI within hours of intake. This effect is due to reduced maternal plasma osmolality, which suppresses vasopressin secretion and promotes fluid redistribution to the amniotic sac. In contrast, isotonic fluids such as normal saline and Ringer’s lactate primarily expand intravascular volume but may not alter osmolality, which limits their effect on foetal urine output. However, both the present review and Gizzo et al. [6] noted that due to heterogeneous data, it is difficult to determine the tangible medical outcome of oral hydration therapy on perinatal outcomes.

A systematic review by Rosemiarti et al. [27], also emphasized oral hydration as an effective intervention for increasing AFI. Their review demonstrated that additional water intake of 1,500–2,500 mL per day significantly improved AFI levels, findings that closely align with our meta-analysis results. Supporting the theory that maternal hydration therapy is a quick and efficient strategy for managing oligohydramnios, our pooled data showed notable AFI increases at multiple times points, including 2 h, 1 day, 2 days and 1 week.

Rosemiarti et al. [27] also emphasized that oral hydration therapy is a safe, non-invasive alternative to amnioinfusion which is hospital based and associated with side effects such as uterine overdistension, chorioamnionitis and premature rupture of membranes. The present systematic review supports their findings, highlighting maternal hydration as the first line management of oligohydramnios, particularly in outpatient and resource-limited settings. Another important aspect of Rosemiarti et al. [27] was the assessment of the dose-response relationship of hydration volume on AFI change. They observed that a daily minimum intake of 1,500 mL resulted in detectable AFI change, while a higher intake of 2,500 mL produced better improvements. Our findings support this point, as the research we looked at in the present review–such as by Patrelli et al. [8] and Malhotra et al. [7] – also showed how increased fluid intake resulted in sustained improvements in amniotic fluid index (AFI). Nevertheless, inconsistent hydration guidelines pose a hurdle; future research should focus on establishing an approach to determine the effective volume, frequency and type of fluids to optimize clinical outcomes.

A key difference between the present review and that of Rosemiarti et al. [27] is the variation in hydration practices across regions. The present systematic review included studies conducted in India, Japan, Iran, Pakistan, Iraq and Italy which involve varying maternal hydration behaviours, climates and diets. By contrast, Rosemiarti et al. [27] reviewed studies mainly from Western and high-income countries, where the baseline hydration may be different. This is an important consideration: baseline hydration status may affect the response to additional fluid intake in pregnancy. In areas with hotter climates and more dehydration risk, maternal hydration therapy may have more benefit in AFI improvement. Future studies should include geographical and lifestyle factors in the assessment of the effectiveness hydration therapy.

A major controversy in maternal hydration therapy is whether oral or IV hydration is more effective. Gizzo et al. [6] arrived at the conclusion that oral hydration, especially with hypotonic solutions, was the most appropriate approach to enhance AFI. For instance, the present systematic review revealed that oral hydration caused substantial AFI increments within 2 h and that intermittent oral fluid intake was required to maintain such increments. However, the studies included in the present review suggested that IV hydration therapy may be more rapid in effect, especially with the use of hypotonic fluids. Doi et al. [9] compared oral and IV hydration and observed that both methods increased AFI but hypotonic IV hydration was more rapid and pronounced. Likewise, Lorzadeh et al. [22] observed that IV hypotonic fluids enhanced AFI to a significantly greater extent than isotonic solutions. These findings are in concordance with the above-mentioned studies which support the view that although oral hydration is efficient and easily available, IV hydration may be advantageous in situations that demand a quick increase in AFI such as severe oligohydramnios or imminent delivery.

The physiological mechanism of the increase in AFI with maternal hydration is primarily related to plasma osmolality and transplacental fluid movement. Flack et al. [26] showed that maternal hydration results in lowered plasma osmolality which in turn reduces vasopressin secretion. This reduction in vasopressin leads to fetal diuresis, an increase in fetal urine output and, therefore higher AFI. Furthermore, it improves uteroplacental perfusion; as a result, there is better placental exchange of fluids and increase in fetal hydration. This improved perfusion helps in sufficient provision of fluid to the fetus and thus maintains normal AFI levels.

Significant heterogeneity in our pooled estimates, particularly at 1 h (I²=94.6 %) and one week (I²=95.8 %) after hydration, necessitates further investigation. Several potential causes of this heterogeneity were identified. First, a significant factor might be the hydration regimens employed in the different studies. These included differences in the frequency of intake (single-time intake vs. repeated daily intake) and the type of fluids (e.g. plain water, ORS, fruit juices, etc.). The physiological response to additional fluid intake may be influenced by the baseline maternal hydration status and the climate, which differ geographically among the included studies (e.g., Japan, Iran, India and Italy). Subgroup analyses were not possible because of the small number of studies that met the requirements for meta-analysis and the irregular reporting of these variables. To better understand the factors causing heterogeneity, we recognize this limitation and emphasize the necessity of future research to standardize baseline hydration status and hydration protocols.

Even though oral hydration therapy seems like a promising low-cost intervention for treating oligohydramnios, it is important to understand its limitations when applying research to clinical practice. We did not stratify outcomes in the present review based on the severity of oligohydramnios (mild, moderate, or severe) because these classifications were not consistently reported in the included studies. There is a substantial evidence gap because most studies do not specify whether the interventions were carried out in inpatient or outpatient settings. This detail is crucial because the cost and effectiveness of oral hydration can vary significantly depending on the circumstances. To make hydration protocols more applicable in real-world situations, future studies should clearly identify the clinical setting and stratify outcomes according to the severity of the illness.

However, there are several limitations to the present systematic review. The heterogeneity among the incorporated research, in terms of study design and the way the outcomes were measured, was a problem in the interpretation of the results. The heterogeneity in the outcome measures used included different AFI cutoff points for diagnosing oligohydramnios and varying lengths of follow up which may have affected the overall effect sizes. Also, most of the included studies investigated third trimester oligohydramnios, thus, there is a lack of information on the possible advantages of hydration therapy at the initial stages of pregnancy. Further research should be directed towards large randomized controlled trials to fill the gaps and provide recommendations for the use of hydration therapy in oligohydramnios. Hydration protocols should also be standardized, the long-term impacts should also be assessed and its efficacy in high-risk pregnancies should also be evaluated as the next steps.

Conclusions

This systematic review and meta-analysis suggests that oral hydration is a non-invasive and easily implementable strategy particularly in low-resource settings where amnioinfusion may not be feasible. In pregnancies complicated by oligohydramnios, oral hydration therapy seems to be a straightforward, non-invasive method that can successfully raise amniotic fluid levels. Although some studies documented positive trends for newborns, like higher Apgar scores and fewer NICU admissions, these results were not consistently measured and should be interpreted cautiously. Future studies should be directed towards establishing the best fluid type, quantity and duration of the therapy to improve the current clinical guidance and perinatal outcomes.