The human digestive system or gastrointestinal tract consists of the mouth, oesophagus, stomach, small intestine, large intestine, and anus. The food is broken down in a series of steps with the help of digestive juices in the digestive system. As a result, the digestive system is a vital organ that breaks down food into small pieces and yields energy. The gut microbiota, or microbiome, is present in healthy people that improve gastrointestinal functions. While gut microbes assist in food absorption and digestion [1,2].
Probiotics consist of live bacteria and yeast that offer a range of health benefits. Probiotics enhance the gut microbiota and immunity and reduce inflammation and allergic reactions . The gut microbiota is closely related to the central nervous system. Probiotics not only restore normal functions of the digestive system, but they also strengthen functions of other organs such as the nervous system, pituitary function and endocrine system .
The prevalence of anxiety, depression, and psychological upset is common in pregnant, perinatal, and postnatal women. However, mental health is the major contributing factor to low birth weight and preterm delivery. Therefore, balancing diet and a safe environment is important for pregnant and lactating women [5–7].
Antenatal nutrition and gestational age are important factors for establishing infant microbiota. In addition, several contributing factors altered the infant gut microbiota, such as preterm delivery, supplementary feeding use of drugs and dietary pattern [8–13]. Probiotic supplementation is a non-pharmacological, non-invasive treatment that benefits both nursing mothers and newborns. Results from an earlier study showed that probiotic supplements significantly reduced infant’s regurgitation, duration of cry and abdominal colic [14–16].
However, only a few systematic reviews and meta-analyses were conducted to evaluate probiotics’ effect on depression symptoms in adults [17,18], prenatal women  and perinatal and postnatal mothers. In addition, pooled the data from previous reviews unclear and retrieved from both randomized control trials (RCTs) and quasi-experimental studies. Therefore, this systematic review and meta-analysis aimed to evaluate the effectiveness of probiotics on mental health and microbiota of newborns.
The review has adopted Cochrane guidelines and reported using the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) . The protocol has been registered with PROSPERO CRD42022372126.
A comprehensive search was conducted using a combination of MeSH terms or keywords connected to the PICO format. The search strategy was carried out using the following keywords: Antenatal women, parity, gravid, pregnant women, perinatal women, intra-natal, postnatal women, lactation mother, breastfeeding mother, neonates, newborn, infants, Lactobacillus acidophilus, probiotics, probiotic supplementation, microbiota, depression, mental health, anxiety, and afraid. Two authors (KH, AS) independently searched the online databases, namely MEDLINE (PubMed), Cumulative Index to Nursing and Allied Health Literature (CINAHL), EMBASE, Web of Science, SCOPUS, and Clinical Key, for RCTs published in the English language from January 2012 to October 2022. The included articles were screened, and duplicate articles were excluded based on review criteria. The reference tracking of relevant articles was manually searched for additional studies.
During the first stage of the search, a total of 18 300 items were identified, and eight studies from citation search with 1309 of them being removed before screening. The remaining studies’ methodology and abstract were screened. A total of 16 991 records, and 16 967 articles and eight citation search articles were excluded as they did not meet the review criteria. Further, we removed six articles due to the unavailability of the full text. Finally, 16 RCTs were included after fulfilling the review criteria: probiotic was the principle intervention for all primary studies published between 2012 and 2022 in the English language. Anxiety and depressions of pregnant and lactating women, as well as neonatal microbiota, were primary outcomes. The reasons for exclusion of primary studies were: probiotics combined with other supplementation and / or not evaluated depression and anxiety, difference in the primary outcome. The flow diagram of the study selection process is depicted in Figure 1.
Figure 1. Flow diagram of study selection.
The Cochrane risk of bias tool-2  was employed to assess the quality of the included RCTs. The details regarding the percentages across the included trials and judgments about each risk of bias item is depicted in Figure 2.
Figure 2. Risk of bias (ROB-2).
Two independent reviewers (KH) extracted the data from the primary studies, and any discrepancies in the initial judgments were confirmed by a third reviewer (LT). The data extraction form included the author’s name, title, year of publication, country, study purpose, sample size, study design, analysis method, risk of bias, and major findings reported by the author(s).
The meta-analysis was performed to examine the effects of probiotic supplementation among pregnant women, lactating mothers, and newborns. Anxiety, depression, and neonatal microbiota were the primary outcomes of the included studies evaluated between the probiotic and placebo groups. The effects of the probiotic intervention were calculated using a random-effects model to compute weighted and standardized mean differences with confidence intervals (CIs) of 95%. The heterogeneity of the included trials was analysed and classified as mild >50%, moderate 50%-75%, and high >75% using the I2 value.
The pooled data of primary studies summarized under the following headings: authors name, year of publication, study design, sample size, type of intervention, and major findings (Table 1).
Table 1. Summary of included studies
RCT – randomized control trial, IG – intervention group, CG – control group, L – lactobacillus, B – bifidobacterium, CFU – colony forming units, BF – breast feeding, y – years, mo – months, d – days, h – hours
This systematic review and meta-analysis comprise 946 pregnant women [22–25], 524 lactating mothers [26–28], and 1678 newborns [29–38]. Sample size of primary studies ranged from 36  to 433 . All original trials adopted double-blinding [22,23,25–27,29–36] except two studies [37,38], reported worldwide, namely New Zealand [22,24,29,30], Finland [25,27], Thailand [31,32], Philippian , the Netherlands , Italy , Istanbul ], South Africa , Germany , USA ] and Poland .
Probiotics administered in pregnant and lactating women
Four trials (n = 946) assessed the effectiveness of probiotics on anxiety and depression among pregnant women [22,23,25] and lactating mother . Probiotics were administered in the first trimester , second trimester [22,24], and third trimester . Probiotics were administered to intervention groups composed of L. rhamnosus HN001 , L. rhamnosus HN001 and B. animalis ssp. lactis 420 , bifidum W23, B. lactis W51, B. lactis W52, Lactobacillus acidophi- lus W37, L. brevis W63, L. casei W56, salivarius W24, L. lactis W19 and L. lactis W58  and L. GG and B. lactis BB12 . Supplementation of probiotics decreased the anxiety and depression in pregnant and lactating women . Also, it reduced mild depression  and improved cognitive functions in pregnant women  (Table 1).
Probiotics administered in lactating mother and newborn
Three studies (n = 524) assessed the effectiveness of probiotics among lactating women and their newborns [26,27,34]. The following probiotics combinations used as interventions such as 9 X 1011 of VSL, L. acidophilus, L. plantarum, L. paracase, L. debrueckii and bulgaricus B. infantis & S. thermophilus  5 X 109 L.GG, 5 X 109 CFU L. rhanmosus LC705, 2 x 108 CFU P freudenreidii ssp, shermani JS  and 5 × 106 actiregulari . Compared to the control group intervention group increases lactobacilli and bifidobacteria in colostrum and mature breast milk  improves gut microbiota  and reduces the duration of cry  (Table 1). Probiotics lower the risk of anxiety and depression in pregnant and lactating women.
Probiotics supplementation in newborns
The remaining nine trials contain full-term, healthy newborns with normal birth weight (n = 1678) and assess the probiotic therapy on neonatal microbiota [23,29–33,35–38]. Three of the nine trials reported newborns delivered via caesarean section (C-section) [29,32,38], while the other six trials reported both C-section and vaginal deliveries [30,31,33,35–37] (Table 1). Probiotics boost the gut microbiota of newborns.
The intervention group received probiotic supplementation in addition to regular breastfeeding for six months. The probiotics are composed of B. bifidum BF3, B. breve BR3, B. longum BG7, B. longu , L. rhamnosus and B. breve [30,32,36,38], Bovin milk derived , oligosaccharides , B. longum  sub. calculated based on an infant’s weights. The intervention group had higher percentages B. lactis , the early development of gut microbiota [30,33,35] or gut emulation , decreased endotoxin levels  or lower stool Ph and high amounts of L-lactate and acetate [32,38].
Probiotics strain, dosages
For pregnant women, the single probiotic strain used was Lactobacillus , and the combined strain was Lactobacillus and Bifidobacterium [22,23,25]. Probiotics provided were based on species namely Bifidobacterium animalis [22,25]. Probiotics provided were based on species namely Bifidobacterium animalis,  or based on genus lactobacillus stated different species Lactobacillus L. rhamnosus [22,24,25] and L. brevis . Probiotic, dosages were expressed in colony forming unit (CFU) per millilitre [30–32], CFU per kilogram [29,35,36] and CFU per day [22,24–27,37,38] (Table 1).
For newborn probiotics, a single strain of the Bifidobacterium [29,37], Lactobacillus , or a combination of Lactobacillus and Bifidobacterium [26,27,36,38]. Similarly, probiotics interventions were based on species, namely Bifidobacterium breve [26,27,32,36,38] Bifidobacterium longum [26,36,37] B. animalis. Based on genus lactobacillus using different species Lactobacillus namely L. acidophilus, L. delbrueckii subsp, L. plantarum, L. reuteri [26,27,36,38] (Table 1).
Only four primary studies reported numerical data on mental health among pregnant and lactating women. Therefore, we selected these trials for the meta-analysis.
Effect of probiotics on anxiety among pregnant and lactating women
Three studies reported the effect of probiotics supplementation on anxiety among pregnant women (n = 676, SMD = 0.01; 95% confidence interval (CI = -0.28,0.30, P = 0.04, I2 = 70) [22,24,25]. Similarly, two studies reported on probiotic usage among lactating women (n = 514, SMD = -0.17; 95% CI = -1.62,1.27, P = 0.00, I2 = 98%) [24,25] (Figure 3).
Figure 3. Effect of probiotics on anxiety.
Effect of probiotics on depression among pregnant and lactating women
Two studies the impact of probiotic supplements on pregnant women’s depression (n = 298, SMD = 0.05; 95% CI = -0.24,0.35, P = 0.20, I2 = 40). Similarly, two studies documented among breastfeeding mothers (n = 518, SMD = -0.10; 95% CI = -1.29,-1.05, P = 0.11, I2 = 60%) [22,25]. However, subgroup analysis was not found to be significant between experimental and control groups (Figure 4).
Figure 4. Effect of probiotics on depression.
This systematic review and meta-analysis evaluated the efficiency of probiotic supplementations for pregnant and lactating women and infant’s microbiota. Supplementation of probiotics in pregnant women has improved mental health [19,39]. There is strong evidence that probiotics benefit the gut and nervous systems, known as the “gut-brain axis” [40,41]. The role of probiotics in alleviating mood and cognition problems is still controversial. Several pieces of evidence support the claim that probiotics benefit both gut and brain health. In addition, recent studies have proved that there is a strong link between the digestive system and the nervous system .
Lactobacillus and Bifidobacterium are probiotic bacteria that have been shown to improve immune system function, respond to the formation of short-chain fatty acids, reduce inflammation, and boost gastric emptying through the action of mucosal receptors .
Probiotics improved the gut microbiota of neonates and reduced abdominal distention, colic and cry duration . Nevertheless, some studies stated probiotics species, namely Lactobacillus, Bifidobacterium, Lactobacillus acidofilus, reuteri, and Streptococcu [45,46]. The dosage of probiotics supplementation was given as follows: 1010 cells for 21 days, 1010 cells for 14 days, and 109 cells for 21 days . Similarly, two studies reported dosages of probiotics 5 × 107, 1.5 × 108, 4.5 × 108, 1.4 × 109, 4.2 × 109 given at first, second, third, fourth and five weeks, respectively [48,49]. Probiotics help in the digestion of newborns and reduce abdominal distension, colic, constipation, necrotizing enterocolitis, and diarrhoea. Specific probiotic strains treat paediatric diseases and are available in capsules, nutrition, and infant formula [50–52].
The main strength of our review is that we included double-blinded, randomized control trials. We also summarized the dosage, strain, and species of probiotics. Our systematic review and meta-analysis revealed that probiotic supplementation is a non-invasive therapy that can be used routinely in prenatal and postnatal women and newborns to improve the physical and mental well-being and microbiota of newborns . Probiotics, prebiotics and synbiotics supplementation reduced prenatal depression , newborn abdominal colic [45,55] and regurgitation .
Various biomarkers and genetic methods are used to create distinct probiotic strains and species to increase neonatal gut microbiota colonisation. As a result, more randomized control trials are needed to investigate the specific probiotic strains used to understand the effects on pregnancy, lactating mothers, and newborns.
There were significant limitations; some studies included C-sections and vaginal births. Original studies did not report numerical data on primary outcomes, especially neonates’ microbiota. Lastly, anxiety and depression decreased in the probiotics group, but the primary studies were unclear about other extraneous variables that may affect mental health in pregnant and lactating women.
Non-invasive therapies, such as probiotics, are more useful to pregnant and breastfeeding women and newborns. Administration of probiotics enhanced the gut microbiota, particularly newborns. The microbiome promotes gut colonization in newborns, influencing digestion and nutrition absorption. Henceforth this study provides strong evidence of the importance of probiotics for prenatal, postnatal, and newborn health.
We would like to thank the Library staff of Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India, for their constant support.