Strengths and Limitations
The strengths of our study were including the large number of trials and
their relatively sample sizes; comprehensive literature covered English
and Chinese; involving all common acupuncture types (TA, EA, TEAS, WA
and LA); more detailed subgroup analyses and meta regression to explore
the heterogeneous; adherence to the intention to treat principle; as
well as robustness of the results to sensitivity analyses. Compared with
the previous and latest reviews published by Coyle ME et al (8 trials,
English-language literature searched up to 3 April 2019) (22) and Xie ZY
et al. (27 trials, literature searched up to December 2018) (15), we
included the largest sample size and most comprehensive trials. Twenty
trials were added in our reviews; eleven had positive results (6, 35,
39, 40, 46, 47, 49, 51, 52, 57, 77), and nine had negative results (30,
42-45, 53-56). In addition, we defined both CPR and LBR as primary
outcomes, which were stricter than CPR alone used in almost all previous
reviews. Compared to CPR, LBR is more likely to reflect the endpoint of
IVF therapy and the most concerned outcome for patients.
A limitation of this review was the significant heterogeneous among
trials. The acupuncture prescription and control type might be the
important contributions to the heterogeneous. Although most acupuncture
prescriptions were generally standardized based on the original protocol
of Paulus et al (57), nearly every study would make appropriate
adjustments to some extent (20). In addition, the type of control
especially for the sham or placebo should be noted. Acupuncture point
location and needle insertion or not are the main factors causing
variance when we establish a sham or placebo acupuncture. In traditional
Chinese medicine theory, acupoint is not a point and has its own domain.
Even though a sham needle is applied away from the acupoint, it might
have the similar treatment effect as the actual acupuncture. Even though
noninvasive placebo acupuncture such as Streitberger acupuncture may
also have certain effects because it stimulates the skin. Those have
been illustrated by our results which suggested CPR and LBR in TA group
were significant compared with no treatment, but no difference compared
with sham or placebo acupuncture. Hence, placebo acupuncture might not
always be an inert control and it is greatly difficult to establish an
ideal placebo acupuncture.