Pregnancy-induced hypertension (PIH) is a significant cause of maternal morbidity [1, 2]. A previous study disclosed that 5.1% of pregnancies are affected by PIH [3]. Furthermore, approximately 15% of global maternal deaths (~30,000 deaths per year) are attributed to hypertensive disorders of pregnancy [4]. Consequently, the prevention and treatment of PIH in urgent in the present study.

Calcium plays a critical role in many vital processes, such as neuronal excitability, the release of neurotransmitters, muscle contraction, membrane integrity, and blood coagulation [5]. In addition, blood pressure is regulated by intracellular calcium in the vascular smooth muscle cell via vasoconstriction and variations in the vascular volume. Therefore, appropriate calcium intake for pregnant women can prevent future osteoporosis and reduces the risk of PIH [6]. However, results reported in previous studies were inconsistent for the relationship between serum calcium level and PIH [7]. Thus, this meta-analysis must confirm the relationship between serum calcium level and PIH.

Our meta-analysis aimed to determine whether or not serum calcium level levels are associated with the risk of PIH, which will offer the basis for the prevention and treatment of PIH.

This study protocol was followed PRISMA guidelines.

A total of 21 potential articles were identified in this study (Table 1, Ref. [11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31] and Fig. 1). NOS was used to assess non-RCT studies (Table 1).

Fig. 1.

PRISMA diagram of the search strategy.

The heterogeneity test found heterogeneity exists (I${}^2$ index = 95%). Then, a random effect model was used to compare the mean serum calcium level between the two groups. The results indicated that the mean serum calcium level in the PIH group was lower than in the control group (p 0.05, Fig. 2, Ref. [11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]).

Fig. 2.

Forest plot and the risk of bias among studies included.

Publication Bias and Sensitivity Analysis

Funnel plots determined publication bias. There was no evidence of publication bias (Fig. 3).

Fig. 3.

Funnel plot and the risk of bias among studies included.

In this meta-analysis, we discovered that the mean serum calcium level in the PIH group was lower than in the control group. The results are consistent with previous results of meta-analysis [32]. Specifically, the serum calcium levels decreased in patients with PIH according to random effects, consistent with an earlier study [5, 33]. A recent study also confirmed that calcium supplementation could effectively reduce the risk of PIH [34, 35].

In recent years, studies have been carried out on serum trace elements levels during pregnancy. PIH is a pregnancy-specific condition that augments maternal and infant mortality and morbidity [36]. Vitamin D can facilitate the absorption of calcium. Thus, vitamin D supplementation also reduces the risk of PIH. Furthermore, a meta-analysis suggested that vitamin D supplementation also works well in preventing PIH [37]. Therefore, measuring serum calcium levels may be a novel way to monitor the risk of PIH.

The strengths of this study include a comprehensive literature search for all relevant No-RCTs, including the content of ordinary pregnant women and pregnancy hypertension women. In addition, we considered effect moderation by trial location and maternal and intervention characteristics. Finally, we reported a broad range of outcomes and considered core outcomes for pregnancy hypertension.

There are some limitations in our meta-analysis. First, this study included only published articles, and some unpublished articles may need to recruit in the present study. Second, this meta-analysis only searched the articles published in Chinese and English. Therefore, language bias also is not avoided. Third, a subanalysis of different phenotypes of hypertensive disorders of pregnancy should be performed [38]. However, this subanalysis is not possible due to a lack of data.

Our research suggests that the reduction in serum calcium concentration may be closely related to PIH. Pregnancy can easily lead to maternal calcium deficiency, increasing blood pressure. Future research should focus on ensuring calcium supplements maintain serum calcium balance and target women with low serum calcium for personalized PIH prevention.

CPL and LPH made contributions to study conception and design; YXS and LPH participated in data collection; LPH and YXS dedicated to data analysis and interpretation; CPL and YXS involved in the drafting of the manuscript. All authors read and approved the final manuscript.

Not applicable.

Thanks to all the peer reviewers for their opinions and suggestions.

This study was supported by the 2022 Taizhou University Higher Education Teaching Reform Project (No. 105 and No. 114).

The authors declare no conflict of interest.