Natural Prevention and Risk Reduction

Evidence Review

Calcium supplementation: Hofmeyr 2018 Cochrane review

The 2018 update of this Cochrane review (Hofmeyr GJ et al., PMID 30277579) pooled 27 studies covering more than 18,000 women comparing high-dose calcium (≥1 g/day) with placebo. Calcium supplementation reduced the risk of preeclampsia by 55 percent overall (average risk ratio 0.45, 95 percent CI 0.31–0.65) with the largest effect in women with low dietary calcium intake (RR 0.36). High blood pressure was reduced by 35 percent, and the composite outcome of maternal death or serious morbidity by approximately 20 percent. The reviewers also analyzed lower-dose calcium (<1 g/day) and found a nonsignificant trend toward benefit, but with weaker evidence. The mechanism is not fully resolved but plausibly involves stabilization of vascular smooth-muscle tone and suppression of parathyroid-hormone–mediated calcium release into vascular cells. [1]

Aspirin: Rolnik 2017 (ASPRE) and Bujold 2010

The ASPRE trial (Rolnik DL et al., NEJM 2017, PMID 28657417) is the strongest single trial of aspirin prevention. Among 26,941 women screened in the first trimester with a multimarker algorithm (maternal factors, mean arterial pressure, uterine artery pulsatility index, PAPP-A and placental growth factor), 1,776 women estimated to have a >1 in 100 risk of preterm preeclampsia were randomized to 150 mg aspirin nightly versus placebo from 11 to 14 weeks until 36 weeks. Preterm preeclampsia (delivery before 37 weeks) occurred in 1.6 percent of the aspirin group versus 4.3 percent of placebo, an odds ratio of 0.38 (95 percent CI 0.20–0.74). The benefit was concentrated in women with at least 90 percent compliance, where the odds ratio fell to 0.24. There were no significant safety differences in maternal bleeding or neonatal complications. [2]

Bujold and colleagues (2010, PMID 20664402) had earlier published a meta-analysis of 34 randomized trials totaling more than 11,000 women. They demonstrated a striking timing effect: aspirin started at or before 16 weeks gestation produced a 53 percent reduction in preeclampsia (RR 0.47), a 90 percent reduction in severe preeclampsia, and a 56 percent reduction in fetal growth restriction. Aspirin started after 16 weeks produced no significant benefit. This timing finding is now embedded in international guidelines. [7]

Vitamin D: Palacios 2019 Cochrane

The 2019 Cochrane review (Palacios C et al., PMID 31348529) pooled 30 trials with 7,033 women. Vitamin D supplementation alone (versus placebo or no intervention) probably reduced preeclampsia (4 trials, 499 women, RR 0.48, 95 percent CI 0.30–0.79; moderate-quality evidence), gestational diabetes (4 trials, 446 women, RR 0.51), and low birth weight (5 trials, 697 women, RR 0.55). Vitamin D combined with calcium versus no supplementation similarly reduced preeclampsia risk. The reviewers noted heterogeneity in dosing and baseline vitamin D status across trials, and called for larger high-quality trials to firm up effect sizes. The plausible mechanisms include vitamin D's role in immune tolerance at the fetal-maternal interface and in vascular and trophoblast function. [4]

Risk stratification: Bartsch 2016 BMJ meta-analysis

Bartsch E et al. (BMJ 2016, PMID 27094586) pooled 92 cohort studies covering 25,356,688 pregnancies. The highest pooled prevalence of preeclampsia was in women with antiphospholipid antibody syndrome (17.3 percent), and the highest pooled relative risks were for prior preeclampsia (RR 8.4), chronic hypertension (RR 5.1), pregestational diabetes (RR 3.7), pre-pregnancy BMI above 30 (RR 2.8), and assisted reproductive technology (RR 1.8). This study underpins the dichotomy of "high risk" (one of these factors warrants aspirin alone) versus "moderate risk" (a combination is needed) used by USPSTF, ACOG, and NICE guidelines. [3]

Physical activity: Aune 2014

Aune D et al. (Epidemiology 2014, PMID 24713878) conducted a systematic review and meta-analysis of 15 cohort and case-control studies. The summary relative risk for high versus low pre-pregnancy physical activity was 0.65 (95 percent CI 0.47–0.89), and for high versus low early-pregnancy activity was 0.79 (0.70–0.91). A dose-response analysis suggested that each 100 minutes per week increment in pre-pregnancy activity was associated with about an 8 percent reduction in preeclampsia risk. The plausible mechanisms include improvements in endothelial function, insulin sensitivity, blood pressure regulation, and reductions in oxidative stress and inflammation. [5]

Omega-3 fatty acids: Middleton 2018 Cochrane

Middleton P et al. (PMID 30480773) pooled 70 trials and 19,927 women. The strongest finding was for preterm birth: omega-3 long-chain polyunsaturated fatty acid supplementation reduced preterm birth before 37 weeks (13.4 percent versus 11.9 percent, RR 0.89, high-quality evidence) and early preterm birth before 34 weeks (4.6 percent versus 2.7 percent, RR 0.58, high-quality evidence). For preeclampsia specifically, the effect was small and not statistically significant in the pooled estimate. Doses across trials ranged from approximately 500 mg to 2.7 g of EPA+DHA per day. The reviewers concluded that omega-3 supplementation is an effective strategy for reducing preterm birth, while recognizing it modestly increases post-term pregnancies (>42 weeks). For preeclampsia, omega-3s are best viewed as part of a healthy dietary pattern rather than a targeted preventive. [6]

What did not work: Roberts 2010 vitamins C and E

Roberts JM et al. (NEJM 2010, PMID 20375405) randomized 10,154 low-risk nulliparous women between 9 and 16 weeks of pregnancy to 1,000 mg vitamin C plus 400 IU vitamin E daily, or placebo, until delivery. The primary outcome — a composite of severe pregnancy-associated hypertension, hypertension with elevated liver enzymes or low platelets, eclampsia, fetal or neonatal death, or perinatal complications — occurred in 6.1 percent of vitamin recipients versus 5.7 percent of placebo (RR 1.07, 95 percent CI 0.91–1.25). There was no benefit on any secondary outcome. Combined with similar negative findings from earlier UK and Australian trials (the VIP and ACTS studies), this established that high-dose antioxidant vitamin supplementation does not prevent preeclampsia. The lesson is broader: a real biological mechanism (oxidative stress) does not guarantee that any intervention claiming to address it will work in practice, and well-designed trials are essential. [8]

Strength of evidence summary

The strongest evidence supports low-dose aspirin (high-quality, large trial plus meta-analyses, large absolute effect in high-risk women), calcium supplementation in low-intake populations (high-quality Cochrane evidence), and physical activity (moderate-quality observational evidence with biological plausibility). Vitamin D supplementation is supported by moderate-quality evidence. Omega-3s have strong evidence for preventing preterm birth and weaker evidence for preeclampsia specifically. Vitamins C and E have been definitively shown not to help. Magnesium supplementation in average-risk women has not shown clear preeclampsia prevention benefit, though intravenous magnesium remains the standard treatment for established severe preeclampsia and eclampsia.

The picture that emerges is consistent with placental health and vascular function being shaped by long-running nutritional and lifestyle inputs, with low-dose aspirin acting on a specific platelet and prostaglandin pathway implicated in early placentation. The interventions that work are inexpensive, widely available, and complementary — and the most reliable strategy is to combine them under the guidance of an obstetrician familiar with each woman's individual risk profile.