Feasibility of acupuncture as an adjunct intervention for ovulatory disorder infertility: A systematic review and meta-analysis

Abstract

BACKGROUND

Acupuncture (AT) is widely used in treatment of ovulatory disorder infertility (ODI), but the safety and efficacy of AT for ODI still lack an evidence-based basis.

AIM

To evaluate the feasibility and effectiveness of AT as an adjunct intervention for ODI.

METHODS

The Cochrane Library, Embase, PubMed, VIP, China National Knowledge Infrastructure, WanFang Data, and Chinese biomedical literature databases were searched from inception to January 20, 2024. Two reviewers independently selected studies, collected data, and evaluated methodological quality through the Cochrane Risk of Bias tool. Revman 5.4 was used for meta-analysis, and the Grade system was performed to evaluate the level of evidence for the outcomes of the meta-analysis.

RESULTS

A total of 20 randomized controlled trials with 1677 ODI patients were included. Compared with the clomiphene citrate (CC) group, the AT plus CC group exhibited significant improvement of the pregnancy rate [relative risk (RR) = 1.68, 95% confidence interval (CI): 1.45-1.95, P < 0.00001, I² = 23%], ovulation rate (RR = 1.34, 95%CI: 1.22-1.47, P < 0.00001, I² = 32%), serum E₂ level [mean difference (MD) = 31.36, 95%CI: 21.83-40.88, P < 0.00001, I² = 97%], thickness of endometrium (MD = 1.76, 95%CI: 0.71-2.81, P = 0.001, I² = 98%) and decreasing miscarriage rate (RR = 0.25, 95%CI: 0.09-0.65, P = 0.005, I² = 0%), serum follicle-stimulating hormone level (MD = -2.10, 95%CI: -3.27 to -0.94, P = 0.0004, I² = 99%), serum luteinizing hormone level (MD = -6.94, 95%CI: -9.89 to -4.00, P < 0.00001, I² = 100%), and serum progesterone level (MD = -1.66, 95%CI: -2.98 to -0.34, P = 0.01, I² = 96%). The AT group had a more favorable effect than CC group for improving pregnancy rate (RR = 1.52, 95%CI: 1.33-1.73, P < 0.00001, I² = 0%), thickness of endometrium (MD = 2.48, 95%CI: 2.15-2.81, P < 0.00001, I² = 0%) and reducing miscarriage rate (RR = 0.23, 95%CI: 0.13-0.44, P < 0.00001, I² = 0%), serum follicle-stimulating hormone level (MD = -0.55, 95%CI: -0.86 to -0.24, P = 0.0005, I² = 0%), and serum progesterone level (MD = -0.24, 95%CI: -0.28 to -0.20, P < 0.00001). However, the level of evidence was predominantly assessed as very low to moderate.

CONCLUSION

AT can improve the pregnancy outcomes and sex hormone levels for patients with ODI. However, further studies are needed to confirm these findings.

Key Words: Acupuncture; Ovulatory disorder; Infertility; Pregnancy; Meta-analysis; Systematic review

Core Tip: Ovulation dysfunction is the most common cause of infertility. This meta-analysis aimed to evaluate the feasibility and effectiveness of acupuncture as an adjunctive intervention to ovulatory disorder infertility (ODI). The results showed that acupuncture effectively improved pregnancy outcomes and sex hormone levels in patients with ODI, indicating its potential as a treatment strategy for ODI. However, further studies are needed to confirm these findings.

INTRODUCTION

Infertility is defined as the failure of a couple of reproductive age to achieve pregnancy after 12 mo of regular unprotected sexual intercourse[1]. For couples over the age of 35, this timeframe is reduced to 6 mo or six menstrual cycles. According to the World Health Organization, ovulation dysfunction is the most common cause of infertility, accounting for approximately 25% of infertility diagnoses[2]. In China, ovulation disorders are responsible for 29.78% of infertility diagnoses[3]. The main mechanism of anovulation and infertility is ovulation disorder caused by abnormal neuroendocrine regulation of the hypothalamic-pituitary-ovarian axis (HPO). The current treatment for ovulatory disorder infertility (ODI) primarily involves induction of ovulation to increase the chances of pregnancy[4].

Clomiphene citrate (CC) is a first-line ovulation induction drug, and it often leads to high output and low pregnancy in clinical application[5]. Long-term oral administration can result in side effects such as ovarian hyperstimulation syndrome (OHSS) and luteinized unruptured follicle syndrome as well as an increased risk of multiple pregnancies, birth defects, and abnormal epigenetic modifications. Moreover, using CC orally for more than 6 mo raises the risk of ovarian cancer[6]. This brings trouble and challenge to the clinical application of CC in the treatment of infertility through ovulation induction. Therefore, identifying effective assisted reproductive techniques to enhance the pregnancy success rate for ODI patients becomes crucial and urgent.

Acupuncture (AT) has garnered attention as a potential treatment for ODI. A 2010 study conducted in the United States revealed that 29% of 428 infertile couples chose complementary and alternative therapies to address their fertility issues. Among these therapies, AT was utilized by 23% and emerged as the most popular alternative approach[7]. Recent clinical randomized trials (RCTs) have demonstrated that AT can stimulate ovulation and enhance reproductive function[8-10]. The potential mechanisms underlying the effectiveness of AT in treating ODI include regulation of the HPO, reduction of inflammation-induced inhibition on follicular development, modulation of Kisspeptin expression levels, improvement of endometrial receptivity, and increased pregnancy rate[11-13].

The limited evidence from a previous meta-analysis compared AT alone or combined with CC for ODI showed no significant improvement in the rate of pregnancy and ovulation, without any observed reduction in miscarriage rate. Notably, this meta-analysis neither analyzed the impact of AT on sex hormone levels nor included an adequate number of studies with satisfactory methodological quality[13]. Therefore, this study aimed to conduct a more comprehensive meta-analysis by combining recently published RCTs to explore the feasibility and effectiveness of using AT for ODI.

MATERIALS AND METHODS

This review was performed following PRISMA guidelines[14] and was registered with INPLASY (registration number: INPLASY202340088, https://inplasy.com/inplasy-2023-4-0088/).

Search strategy

Cochrane Library, Embase, PubMed, VIP, China National Knowledge Infrastructure, WanFang Data, and Chinese biomedical literature databases were searched from inception to January 20, 2024. The retrieval strategy was determined after several preliminary searches using a combination of subject terms and free words. The search terms used were “acupuncture,” “ovulation disorders,” and “infertility.” Table 1 summarizes the search strategy for PubMed, with adjustments made for other electronic databases based on their specifications. The search strategies were shown in the supplementary material.

Table 1 Search strategy for PubMed.

Search	Terms
1	“Infertility” (MeSH Terms)
2	“Infertility” (Title/Abstract) OR “Infertile” (Title/Abstract) OR “Sterility” (Title/Abstract) OR “Sterile” (Title/Abstract)
3	1 OR 2
4	“Anovulation” (MeSH Terms)
5	“Ovulatory dysfunction” (Title/Abstract) OR “Anovulation” (Title/Abstract) OR “Anovulatory” (Title/Abstract) OR “Ovulatory disorders” (Title/Abstract) OR “Ovulation failure” (Title/Abstract) OR “Ovarian stimulation” (Title/Abstract) OR “Ovarian induction” (Title/Abstract)
6	4 OR 5
7	“Acupuncture” (MeSH Terms)
8	“Acupuncture” (Title/Abstract) OR “Acupuncture Therapy” (Title/Abstract) OR “Auricular Points” (Title/Abstract) OR “Ear acupuncture” (Title/Abstract) OR “Electroacupuncture” (Title/Abstract) OR “Electro-acupuncture” (Title/Abstract) OR “Meridians” (Title/Abstract) OR “Acupuncture Points” (Title/Abstract) OR “Acupressure” (Title/Abstract) OR “Auricular” (Title/Abstract) OR “Acusector” (Title/Abstract) OR “Needle” (Title/Abstract) OR “Fire Needle” (Title/Abstract) “Acupoint catgut embedding” (Title/Abstract) OR “Moxibustion” (Title/Abstract) OR “Scalp acupuncture points” (Title/Abstract) OR “Bleeding” (Title/Abstract) OR “Acupoint injection” (Title/Abstract) OR “Needle knife” (Title/Abstract)
9	7 OR 8
10	(“Randomized controlled trial” (Publication Type) OR “Controlled clinical trial” (Publication Type) OR “Randomized” (Title/Abstract) OR “Placebo” (Title/Abstract) OR “Clinical trials as topic” (MeSH Terms) OR “Randomly” (Title/Abstract) OR “Trial” (Title)) NOT “Animals” (MeSH Terms) NOT “Humans” (MeSH Terms)
11	3 AND 6 AND 9 AND 10

Inclusion and exclusion criteria

The inclusion criteria were: (1) Participants (P). Patients diagnosed with ODI. The diagnostic criteria were followed by the Obstetrics and Gynecology, published by the People’s Medical Publishing House in 2013[15] and Guiding Principles for Clinical Research on New Chinese Medicines, published by the China Pharmaceutical Science and Technology Press in 2002[16]; (2) Intervention (I). Intervention groups received AT alone or combined with CC; (3) Control (C). Control groups should be CC; (4) Outcome (O). Outcomes included ovulation rate, pregnancy rate, miscarriage rate, follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E₂), progesterone (P), thickness of endometrium, and adverse events; and (5) Study (S). RCTs.

Exclusion criteria: (1) Not RCTs, including animal studies, review articles, and case reports; (2) Repeat published studies; (3) Patients who do not meet the diagnostic criteria for ODI; (4) Use of other drugs that may affect ovulation; and (5) Studies with no reported relevant data.

Data extraction and quality assessment

Two researchers (Chen YQ and Shen T) independently reviewed the titles and abstracts of identified trials and excluded irrelevant literature. Any uncertainties were resolved through a detailed examination of the full text, followed by data extraction and cross-verification. Potential conflicts were addressed through discussion with a third researcher (Lv Y). The extracted information included details such as first author, publication date, sex distribution, sample size, age range, intervention measures, outcomes, etc. The Cochrane Collaboration tool was used to evaluate the quality of the included studies. The content included the random sequence, allocation concealment, blinding (including blinding of researchers and participants, and blind evaluation of study results), the integrity of the results, selective reporting of study results, and other bias. Each item was judged by low risk, high risk, and unclear.

Data analysis

The Revman 5.4 software was used for meta-analysis. Relative risk (RR) was employed as the effect indicator for binary variables, and mean difference (MD) was utilized as the effect indicator for continuous variables. For each effect size, its point estimate and a 95% confidence interval (CI) were presented. A heterogeneity test was performed by χ² test, and the test level was P = 0.05. The studies showed no statistical heterogeneity (P > 0.10, I² < 50%), thus the fixed-effect model was applied for analysis; otherwise, the random-effects model was used instead. If more than ten trials were included, publication bias was analyzed by funnel plot. To determine whether the type of experimental intervention (AT plus CC vs CC or AT vs CC) affected the efficacy of AT, we planned to perform a subgroup meta-analysis. The grade guideline was performed to summarize the quality of evidence for the outcomes of the meta-analysis.

RESULTS

Search and selection

A total of 643 potentially eligible studies were collected, and 249 duplicate studies were removed by Endnote 20. According to the inclusion and exclusion criteria, 207 studies were removed after screening by title and abstract. After reading the full text, 42 studies were deleted, and 20 studies were finally included[17-36]. The literature screening process is shown in Figure 1.

Figure 1  Literature screening flowchart.

Characteristics of the included studies

Twenty trials with 1677 patients were included. There were 840 patients in the treatment group and 827 patients in the control group. The minimum sample size was 52 and the maximum was 179. The included trials varied in terms of outcomes, including pregnancy rate[17,18,20-23,25-36], ovulation rate[19,21-23,25,26,28,30-33,35], miscarriage rate[20,21,23,26,28-30,32,34-36], FSH levels[17-19,22,24,25,28,33], LH levels[17-19,22,24,25,28,33], E₂ levels[18,19,22,24,25,28,33], P levels[17-19,25], thickness of endometrium[22,24,25,27,28,32-34,36], and adverse events[25-28,33,34]. Detailed characteristics of the studies are shown in Table 2.

Table 2 The characteristics of included studies.

Ref.	Sample size	Mean age in yr	Course of disease in yr	Intervention	Details of AT	Acupoint	Comparison	Duration	Outcomes
Su et al[17], 2022	T: 30, C: 30	T: 29.50 ± 2.50, C: 28.45 ± 2.50	NR	AT plus CC	Every other day, 5 consecutive times/starting on day 5 after the end of menstruation	RN4, RN6, Zigong, BL23, BL31, BL32, BL33, BL34, SP6	CC, 50 mg/tid, for 5 d, starting on day 5 after the end of menstruation	4 MC	1,4,5,7
Zhu and Xiang[18], 2022	T: 47, C: 51	T: 30 ± 3, C: 29 ± 3	T: 2.41 ± 1.37, C: 2.39 ± 1.42	AT plus CC	30 min, each day/until 1 wk before the next MC	RN4, Zigong, SP10, GV4, BL23, BL32, ST36, SP6, KI1, KI3, PC8	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1,4,5-7
Cui et al[19], 2022	T: 28, C: 28	T: 26.53 ± 3.11, C: 26.25 ± 3.01	T: 2.09 ± 0.29, C: 2.05 ± 0.27	AT plus CC	Starting on day 4 after the end of menstruation	BL31, BL32, BL33, BL34	CC, 50 mg/qd, for 5 d, starting on day 4 after the end of menstruation	3 MC	2,4-7
Li[20], 2015	T: 51, C: 51	T: 23.2 ± 0.5, C: 2.0 ± 0.6	T: 23.4 ± 0.6, C: 2.2 ± 0.9	AT	30 min, each day, for 10 d/starting on day 5 after the end of menstruation	RN3, RN4, RN8, ST36, Zigong, SP6	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1,3
Song et al[21], 2008	T: 60, C: 60	T: 28.60 ± 3.74, C: 28.30 ± 3.67	T: 3.75 ± 1.94, C: 3.69 ± 1.83	AT	30 min, each day, for 10 d/starting on day 5 after the end of menstruation	RN3, RN4, RN8, Zigong, ST36, SP6	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1-3
Zhang[22], 2019	T: 53, C: 53	T: 29 ± 4, C: 29 ± 4	T: 3.50 ± 0.43, C: 3.47 ± 0.41	AT plus CC	Starting on day 5 after the end of menstruation, every other day/until the next MC	BL23, GV4, RN3, RN4, ST25, ST29, SP6	CC, 50 mg/tid, for 5 d, starting on day 2-5 after the end of menstruation or day 6 of withdrawal bleeding	3 MC	1,2,4-6,8
Amina·and Yang[23], 2011	T: 66, C: 66	NR	NR	AT	30 min, each day, for 10 d/starting on day 5 after the end of menstruation	RN3, RN4, Zigong, ST36, SP6	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1-3
Zhong and Chen[24], 2017	T: 38, C: 38	T: 30.84 ± 1.64, C: 31.02 ± 1.56	T: 7.30 ± 1.27, C: 7.23 ± 1. 31	AT plus CC	30 min, each day, for 10 d/starting on day 5 after the end of menstruation	RN3, RN4, RN8, SP6, Zigong, ST36, LR3, KI3	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	2 MC	4-6,8
Yuan[25], 2022	T: 36, C: 36	T: 27.19 ± 2.58, C: 27.67 ± 2.74	T: 3.33 ± 1.88, C: 3.19 ± 1.26	AT	30 min, 6 times per week /starting on day 5 after the end of menstruation	RN4, RN5, BL20, BL23, SP6	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1,2,4-9
Zheng[26], 2019	T: 35, C: 35	T: 30.24 ± 3.05, C: 29.25 ± 3.53	T: 27.59 ± 12.20 m, C: 27.03 ± 11.34 m	AT plus CC	30 min, every other day/starting on day 5 after the end of menstruation	ST25, ST36, RN3, RN4, RN5, SP6, K13, BL20, BL23, LR03	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1-3,9
Zhu[27], 2017	T: 30, C: 30	T: 32.17 ± 3.23, C: 33.07 ± 3.13	T: 5.23 ± 3.21, C: 5.73 ± 2.10	AT plus CC	30 min, each day/starting on day 5 after the end of menstruation	ST25, ST28, ST36, SP6, RN7, RN9	CC, 50 mg/qd, for 3 d, starting on day 5 after the end of menstruation	3 MC	1,8,9
Su[28], 2016	T: 33, C: 33	T: 31.00 ± 4.57, C: 29.83 ± 4.99	NR	AT	20-30 min, once every 3 d/starting on day 5 after the end of menstruation	RN10, RN12, RN4, RN5, ST28, Zigong	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1-6,8,9
Liu[29], 2018	T: 26, C: 26	T: 32.1 ± 5.5,C: 31.5 ± 5.8	T: 3.4 ± 1.1, C: 3.2 ± 1.2	AT plus CC	30 min, each day, for 7 d/starting on day 5 after the end of menstruation	RN8, Zigong, RN4, RN3, SP6, ST36	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1,3
Wang[30], 2014	T: 50, C: 50	T: 28.70 ± 3.75, C: 28.40 ± 3.68	T: 3.76 ± 1.95, C: 3.70 ± 1.85	AT	30 min, each day, for 10 d/starting on day 6 after the end of menstruation	RN4, RN8, SP6, Zigong, RN3	CC, 50 mg/qd, for 5 d, starting on day 6 after the end of menstruation	3 MC	1-3
Danniyaer[31], 2023	T: 32, C: 32	T: 33.93 ± 3.59, C: 34.14 ± 3.51	T: 3.44 ± 1.12, C: 3.25 ± 1.17	AT plus CC	Starting on day 5 after the end of menstruation	RN4, RN3, Zigong, ST36	CC, 50 mg/qd, for 5 d, starting on day 5 after the end of menstruation	3 MC	1,2
Zhai[32], 2016	T: 30, C: 30	T: 28.26 ± 3.96, C: 28.45 ± 3.87	T: 3.37 ± 1.36, C: 3.52 ± 1.57	AT plus CC	20 min, each day, for 5 d/starting on day 5 after the end of menstruation	LI4, SP9, ST36, SP6	CC, 50 mg/qd, for 5 d, starting on 5 after the end of menstruation	3 MC	1-3,8,9
Wei et al[33], 2010	T: 93, C: 86	T: 33.0 ± 2.4, C: 31.0 ± 3.8	T: 7.0 ± 1.5, C: 7.0 ± 1.1	AT plus CC	40 min, every other day/starting on day 5 after the end of menstruation	RN4, Zigong, SP10, SP6, KI3, ST36, LI4, LR3	CC, 50 mg/qd, for 5 d, starting on 5 after the end of menstruation	3 MC	1,2,4-6,8,9
Zhou[34], 2019	T: 32, C: 32	T: 26.97 ± 3.85, C: 27.50 ± 2.58	T: 2.00 ± 1.58, C: 1.37 ± 0.81	AT plus CC	30 min, 3 times per week/starting on day 5 after the end of menstruation	RN4, RN3, Zigong, SP6	CC, 50 mg/qd, for 5 d, starting on 5 after the end of menstruation	3 MC	1,3,8,9
Zheng et al[35], 2007	T: 40, C: 40	T: 27.6 ± 7.6, C: 28.1 ± 7.4	T: 3.7 ± 4.1, C: 3.8 ± 4.1	AT	30 min, starting on day 5 after the end of menstruation	RN8, RN3, RN4, Zigong, ST36, SP6	CC, 50 mg/qd, for 5 d, starting on 5 after the end of menstruation	3 MC	1-3
Zhou et al[36], 2018	T: 30, C: 30	T: 29.3, C: 29.3	NR	AT	Each day, for 10 d/starting on day 5 after the end of menstruation	SP6, K17, BL23	CC, 50-100 mg/qd, for 5 d, starting on 5 after the end of menstruation	1 MC	1,3,8

¹Pregnancy rate; ²Ovulation rate; ³Miscarriage rate; ⁴Follicle-stimulating hormone; ⁵Luteinizing hormone; ⁶Estradiol; ⁷Progesterone; ⁸Thickness of endometrium; ⁹Adverse events. AT: Acupuncture; C: Control group; m: month; CC: Clomiphene citrate; MC: Menstrual cycles; NR: Not reported; T: Treatment group.

AT protocols in included trials

A total of 12 trials[17-19,22,24,26,27,29,31-34] used AT plus CC, and 8 trials[20,21,23,25,28,30,35,36] used AT. All included trials described acupoint selection. As shown in Figure 2, the top five acupoints with the highest frequency were Sanyinjiao (SP 6), Guanyuan (RN 4), Zigong, Zusanli (ST36), and Zhongji (RN 3). The residence time of the needle ranged from 20-40 min. The frequency of treatment was each day[18,20,21,23,24,27,29-32,35,36], every other day[17,22,26,33], once every 3 d[28], 3 times per week[34], and 6 times per week[25]. The duration of treatment was 2 to 4 menstrual cycles. A total of 20 trials highlighted Deqi, a unique AT sensation that is critical for clinical efficacy.

Figure 2  Acupoints selection of included randomized controlled trials.

Methodological quality

Among the included 20 trials, 10 trials[18,20,22,24,26,28,31-34] used the random number table method, 6 trials[17,19,25,27,29,36] only mentioned randomization without describing the specific randomization method, and 4 trials[21,23,30,35] used the order randomization method. Allocation concealment was mentioned in only one trial[34]. Blinding was reported in only two trials[17,34]. Two trials[17,21] reported selective reporting. Figure 3 illustrates the risk of bias in included trials.

Figure 3 Risk of bias assessment of included studies. A: Graph; B: Bias summary.

Meta-analysis results

AT plus CC vs CC: (1) Pregnancy rate. Ten trials involving 790 ODI patients compared the pregnancy rate between AT plus CC and CC. The fixed-effect model indicated that the pregnancy rate of AT plus CC was significantly higher than CC (RR = 1.68, 95%CI:1.45-1.95, P < 0.00001), and heterogeneity in the pregnancy rate was low (I² = 23%, P = 0.23) (Figure 4); (2) Ovulation rate. Six trials involving 1042 ODI patients compared the ovulation rate between AT plus CC and CC. The fixed-effect model indicated that the ovulation rate of AT plus CC was significantly higher than CC (RR = 1.34, 95%CI: 1.22-1.47, P < 0.00001), and heterogeneity in the ovulation rate was low (I² = 32%, P = 0.19) (Figure 5); (3) Miscarriage rate. Four trials involving 102 ODI patients compared the miscarriage rate between AT plus CC and CC. The fixed-effect model indicated that the miscarriage rate of AT plus CC was superior to CC (RR = 0.25, 95%CI: 0.09-0.65, P = 0.005), and heterogeneity in the miscarriage rate was low (I² = 0%, P = 0.76) (Figure 6); (4) FSH. Six trials involving 572 ODI patients compared the serum FSH level between AT plus CC and CC. The random-effect model indicated that the serum FSH level of AT plus CC was significantly lower than CC (MD = -2.10, 95%CI: -3.27 to -0.94, P = 0.0004), and heterogeneity in the serum FSH level was significant (I² = 99%, P < 0.00001) (Figure 7A); (5) LH. Six trials involving 572 ODI patients compared the serum LH level between AT plus CC and CC. The random-effect model indicated that the serum LH level of AT plus CC was noticeably lower than CC (MD = -6.94, 95%CI: -9.89 to -4.00, P < 0.00001), and heterogeneity in the serum LH level was significant (I² = 100%, P < 0.00001) (Figure 7B); (6) E₂. Five trials involving 515 ODI patients compared the serum E₂ level between AT plus CC and CC. The random-effect model indicated that the serum E₂ level of AT plus CC was significantly higher than CC (MD = 31.36, 95%CI: 21.83-40.88, P < 0.00001), and heterogeneity in the serum E₂ level was significant (I² = 97%, P < 0.00001) (Figure 7C); (7) P. Three trials involving 211 ODI patients compared the serum P level between AT plus CC and CC. The random-effect model indicated that the serum P level of AT plus CC was significantly lower than CC (MD = -1.66, 95%CI: -2.98 to -0.34, P = 0.01), and heterogeneity in the serum P level was significant (I² = 96%, P < 0.00001) (Figure 7D); and (8) Thickness of endometrium. Six trials involving 538 ODI patients compared the thickness of endometrium between AT plus CC and CC. The random-effect model indicated that the thickness of endometrium of AT plus CC was significantly higher than CC (MD = 1.76, 95%CI: 0.71-2.81, P = 0.001), and heterogeneity in the thickness of endometrium was significant (I² = 98%, P < 0.00001) (Figure 8).

Figure 4 Forest plot of the effects of acupuncture plus clomiphene citrate vs clomiphene citrate on pregnancy rate. CC: Clomiphene citrate; CI: Confidence interval.

Figure 5 Forest plot of the effects of acupuncture plus clomiphene citrate vs clomiphene citrate on ovulation rate. CC: Clomiphene citrate; CI: Confidence interval.

Figure 6 Forest plot of the effects of acupuncture plus clomiphene citrate vs clomiphene citrate on miscarriage rate. CC: Clomiphene citrate; CI: Confidence interval.

Figure 7 Forest plot of the effects of acupuncture plus clomiphene citrate vs clomiphene citrate on follicle stimulating hormone, luteinizing hormone, estradiol, and progesterone. A: Follicle stimulating hormone; B: Luteinizing hormone; C: Estradiol; D: Progesterone. CC: Clomiphene citrate; CI: Confidence interval.

Figure 8 Forest plot of the effects of acupuncture plus clomiphene citrate vs clomiphene citrate on the thickness of the endometrium. CC: Clomiphene citrate; CI: Confidence interval.

AT vs CC: (1) Pregnancy rate. Eight trials involving 706 ODI patients compared the pregnancy rate between AT and CC. The fixed-effect model indicated that the pregnancy rate of AT was significantly higher than CC (RR = 1.52, 95%CI: 1.33-1.73, P < 0.00001), and heterogeneity in the pregnancy rate was low (I² = 0%, P = 0.92) (Figure 9); (2) Ovulation rate. Six trials involving 1151 ODI patients compared the ovulation rate between AT and CC. The random-effect model indicated that the ovulation rate of AT was not significantly different than CC (RR = 0.95, 95%CI: 0.87-1.04, P = 0.27), and heterogeneity in the ovulation rate was significant (I² = 73%, P = 0.002) (Figure 10); (3) Miscarriage rate. Seven trials involving 376 ODI patients compared the miscarriage rate between AT and CC. The fixed-effect model indicated that the miscarriage rate of AT was superior to CC (RR = 0.23, 95%CI: 0.13-0.44, P < 0.00001), and heterogeneity in the miscarriage rate was low (I² = 0%, P = 0.98) (Figure 11); (4) FSH. Two trials involving 134 ODI patients compared the serum FSH level between AT and CC. The fixed-effect model indicated that the serum FSH level of AT was significantly lower than CC (MD = -0.55, 95%CI: -0.86 to -0.24, P = 0.0005), and heterogeneity in the serum FSH level was low (I² = 0%, P = 97) (Figure ); (5) LH. Two trials involving 134 ODI patients compared the serum LH level between AT and CC. The random-effect model indicated that the serum LH level of AT was not significantly different than CC (MD = -0.17, 95%CI: -1.891.54, P = 0.84), and heterogeneity in the serum LH level was significant (I² = 95%, P < 0.00001) (Figure ); (6) E₂. Two trials involving 134 ODI patients compared the serum E₂ level between AT and CC. The random-effect model indicated that the serum E₂ level of AT was not significantly different than CC (MD = 6.09, 95%CI: -5.28-17.47, P = 0.29), and heterogeneity in the serum E₂ level was significant (I² = 98%, P < 0.00001) (Figure ); (7) P. One study involving 72 ODI patients compared the serum P level between AT and CC. The fixed-effect model indicated that the serum P level of AT was significantly lower than CC (MD = -0.24, 95%CI: -0.28 to -0.20, P < 0.00001) (Figure ); and (8) Thickness of endometrium. Three trials involving 194 ODI patients compared the thickness of endometrium between AT and CC. The fixed-effect model indicated that the thickness of endometrium of AT was significantly higher than CC (MD = 2.48, 95%CI: 2.15, 2.81, P < 0.00001), and heterogeneity in the thickness of endometrium was low (I² = 0%, P = 0.63) (Figure 13).

Figure 9 Forest plot of the effects of acupuncture vs clomiphene citrate on pregnancy rate. CC: Clomiphene citrate; CI: Confidence interval.

Figure 10  Forest plot of the effects of acupuncture vs clomiphene citrate on ovulation rate. CC: Clomiphene citrate; CI: Confidence interval.

Figure 11  Forest plot of the effects of acupuncture vs clomiphene citrate on miscarriage rate. CC: Clomiphene citrate; CI: Confidence interval.

Figure 12  Forest plot of the effects of acupuncture vs clomiphene citrate on follicle stimulating hormone, luteinizing hormone, estradiol, and progesterone. A: Follicle stimulating hormone; B: Luteinizing hormone; C: Estradiol; D: Progesterone. CC: Clomiphene citrate; CI: Confidence interval.

Figure 13  Forest plot of the effects of acupuncture vs clomiphene citrate on thickness of endometrium. CC: Clomiphene citrate; CI: Confidence interval.

Adverse effect

Six trials including 511 ODI patients reported adverse events[25-28,33,34]. Four trials did not describe the occurrence of adverse events. Two trials observed the occurrence of OHSS. There was no statistically significant difference in the incidence of OHSS between the two groups (Odds ratio = 0.30, 95%CI: 0.04 -1.95, P = 0.20) (Figure 14).

Figure 14  Forest plot and meta-analysis of adverse events. CI: Confidence interval.

Publication bias

The publication bias of pregnancy rate outcome was evaluated by funnel plots of AT plus CC vs CC based on the analysis of 10 trials. Funnel plot asymmetry was observed, indicating no significant evidence of publication bias (Figure 15). Due to the limited inclusion of studies, other outcomes were not evaluated for publication bias.

Figure 15  Funnel plots of acupuncture plus clomiphene citrate vs clomiphene citrate on pregnancy rate. SE: Standard error; RR: Relative risk.

Grade assessment

Table 3 summarizes the detailed ratings and reasons for the downgrade. The overall certainty of the quality of evidence was categorized as very low to moderate.

Table 3 Grade of evidence of outcomes of the included trials.

Outcomes	Certainty assessment						Effect sizes	Certainty	Importance
	Number of trials (patients)	Risk of bias1	Inconsistency2	Indirectness3	Imprecision4	Publication bias5	RR or MD (95%CI)
AT plus CC vs CC
Pregnancy	10 (790)	Serious	No serious	No serious	No serious	Likelihood	RR 1.68 (1.45-1.95)	Moderate6	Critical
Ovulation	6 (1042)	Serious	No serious	No serious	No serious	Undetected	RR 1.34 (1.22-1.47)	Moderate6	Critical
Miscarriage rate	4 (102)	Serious	No serious	No serious	Serious	Undetected	RR 0.25 (0.09-0.65)	Low7	Critical
FSH	6 (572)	Serious	Serious	No serious	No serious	Undetected	MD -2.10 (-3.27 to -0.94)	Low7	Important
LH	6 (572)	Serious	Serious	No serious	No serious	Undetected	MD -6.94 (-9.89 to -4.00)	Low7	Important
E2	5 (515)	Serious	Serious	No serious	No serious	Undetected	MD 31.36 (21.83-40.88)	Low7	Important
P	3 (211)	Serious	Serious	No serious	Serious	Undetected	MD -1.66 (-2.98 to -0.34)	Very low8	Important
Thickness of endometrium	6 (538)	Serious	Serious	No serious	No serious	Undetected	MD 1.76 (0.71-2.81)	Low7	Important
AT vs CC
Pregnancy	8 (706)	Serious	No serious	No serious	No serious	Undetected	RR 1.52 (1.33-1.73)	Moderate	Important
Ovulation	6 (1151)	Serious	Serious	No serious	No serious	Undetected	RR 0.95 (0.87-1.04)	Low7	Important
Miscarriage rate	7 (376)	Serious	No serious	No serious	Serious	Undetected	RR 0.23 (0.13-1.04)	Low7	Important
FSH	2 (134)	Serious	Serious	No serious	Serious	Undetected	MD -0.55 (-0.86 to -0.24)	Very low8	Important
LH	2 (134)	Serious	Serious	No serious	Serious	Undetected	MD 3.27 (1.55-4.99)	Very low8	Important
E2	2 (134)	Serious	Serious	No serious	Serious	Undetected	MD 2.19 (1.10-3.28)	Very low8	Important
P	1 (72)	Serious	Undetected	No serious	Serious	Undetected	MD 3.02 (1.33-4.71)	Low7	Important
Thickness of endometrium	3 (194)	Serious	Serious	No serious	Serious	Undetected	MD 2.06 (1.23-2.89)	Very low8	Important

¹Risk of bias: Serious, study with unclear risk of bias.

²Inconsistency: Serious, I² > 50%.

³Indirectness: No indirectness of evidence was found in any study.

⁴Imprecision (based on sample size): Serious, n < 500 participants.

⁵Publication bias: Undetected due to the number of trials less than the recommended arbitrary minimum number of 10.

⁶Moderate: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.

⁷Low: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.

⁸Very low: We are very uncertain about the estimate. AT: Acupuncture; CC: Clomiphene citrate; CI: Confidence interval; E₂: Estradiol; FSH: Follicle-stimulating hormone; LH: Luteinizing hormone; MD: Mean difference; P: Progesterone; RR: Risk ratio.

DISCUSSION

This review evaluated the possibilities and advantages of AT for ODI, including 20 studies with 1677 patients. The results of this review demonstrating the effect of AT in improving pregnancy outcomes in patients with ODI are consistent with the previous review[13]. Unlike the previous review[13], studies that used other Teding dianci bopu traditional Chinese medicine interventions in the intervention group were excluded from this review because the potential harms and benefits of these interventions are not known. Ten recently published studies were added to this review to provide important evidence updates. In addition, we further analyzed the improvement effect of AT on sex hormone levels and ovarian function. Compared to CC alone, AT as an adjunctive treatment can significantly increase the pregnancy rate and ovulation rate by approximately 68% and 34%, respectively, while also improving serum E₂ levels and endometrial thickness. In addition, adjuvant AT also significantly reduced serum FSH, LH, and P levels and 25% miscarriage rate. In the comparison of AT with CC, AT could significantly improve endometrial thickness and pregnancy rate by 52%. It was more beneficial in reducing serum FSH and P levels and 23% miscarriage rate. There was no significant difference between AT and CC in reducing the incidence of adverse effects.

For a long time, AT has been widely used to treat infertility, and several potential mechanisms have been demonstrated to explain its effects. AT in the treatment of ODI can regulate the endocrine level of patients, significantly increase the level of β-endorphin, improve the blood supply of the ovarian artery, promote endometrial development, promote blastocyst implantation, and achieve the purpose of increasing the pregnancy rate and reducing the early abortion rate[37,38].

Chen et al[39] found that AT regulated ovarian granulosa cell autophagy by downregulating LncMEG3 expression and inhibiting the PI3K/AKT/mTOR pathway, thereby improving ovarian development and sex hormone levels and possibly treating ovulation dysfunction. Zhang et al[40] found that electroacupuncture regulated serum E₂, FSH, and LH levels and improved ovarian function by activating the PI3K/AKT/mTOR signaling pathway.

Fu et al[41] found that AT reduced the increase in serum E₂ levels and increased the decreased pituitary estrogen receptor expression in the superovulatory rat model, enhanced the function of the HPO axis, and prevented and reduced the occurrence of OHSS. Studies have shown that AT can promote follicle growth, rupture, and excretion and improve endometrial receptivity. AT treatment of ODI is closely related to its regulation of the reproductive axis and increase of the endometrial blood supply[42].

In addition, this review found that SP 6, RN 4, Zigong, ST 36, and RN 3 seemed to be the most commonly used acupoints for AT treatment of ODI. The most common treatment number was each day (65%), and the duration was 30 min (80%). It is suggested that in future studies, priority should be given to the above acupoints and the number and duration of treatment.

SP6 is the essential point of the spleen meridian of foot-taiyin, which is the intersection point with the kidney, liver and spleen three Yin meridians. It can invigorate the spleen and regulate blood, soothe the liver and nourish the kidney, and regulate and replenish the thoroughgoing conception vessel. Studies have confirmed that the SP6 and RN4 acupoints of AT ovariectomy rats can regulate the disorder of serum endocrine hormones and improve the dysfunction of the HPO axis[43].

RN4 is the intersection point between conception vessel and kidney, liver, spleen, three Yin meridians, and the thoroughgoing vessel, which can regulate qi and blood of all meridians, strengthen the yuan, strengthen the root, and replenish the lower jiao. The RN4 acupoint can regulate the pituitary and gonadal functions by affecting the secretion of gonadotropin-releasing hormone from the hypothalamus in female AT rats[44].

The Zigong point is a special extrameridian point, which is not only located near the uterus in the lower abdomen but also closely related to the uterus in its neuroanatomical structure. It is an important point for the treatment of gynecological and obstetrical diseases and has a significant clinical effect on infertility and other uterine diseases[45].

ST36 can warm up the innate and acquired vitality, and SP6 matches and can supplement the liver and kidney, promote blood circulation, and regulate menstruation. The results showed that AT in ST36 reduced the serum levels of interleukin-6 and tumor necrosis factor α in animals, which may be related to the ability of AT to inhibit inflammation and oxidative stress[46].

RN3 is the intersection point of conception vessel and kidney, liver and spleen three Yin meridians, which affects the uterus and sperm chamber, and can lead to human reproductive diseases. It has been shown that continuous electroacupuncture stimulation of RN4 and RN3 can reduce the expression of P450c17α in the theca cell layer and downregulate the levels of testosterone, androstenedione, and LH, thereby improving follicular development and ovulation[47].

Although from a clinical perspective, the results of this meta-analysis support the use of AT in patients with ODI, there were some limitations: (1) Few studies discussed how to estimate the sample size, and most studies involved small sample sizes leading to low accuracy; (2) The quality of most of the literatures was low, and no specific randomization method was defined; (3) Some studies did not adequately report allocation concealment. Failure to fully implement allocation concealment may overstate any treatment effect observed; (4) The search scope was not wide enough, the clinical trial platform was not searched, the grey literature was not collected, and the results of the included literature were all positive, which may affect the results of the meta-analysis; and (5) Lack of follow-up. For example, 18 studies reported the pregnancy rate but did not report the live birth rate and neonatal health status.

CONCLUSION

AT can improve the pregnancy outcomes and sex hormone levels for patients with ODI. However, further studies are needed to confirm these findings.