Preeclampsia is defined as the combination of high blood pressure (hypertension), swelling (edema), and protein in the urine (albuminuria, proteinuria) developing after the 20th week of pregnancy.¹ Preeclampsia ranges in severity from mild to severe; the mild form is sometimes called proteinuric pregnancy-induced hypertension² or proteinuric gestational hypertension.³

Women with even mild preeclampsia must be monitored carefully by a healthcare professional. Hospitalization may be necessary to enable close observation.⁴

In severe preeclampsia, symptoms are more pronounced. Severe preeclampsia may lead to eclampsia, which causes seizures and can cause death of both the mother and fetus if left untreated.⁵ Like eclampsia, severe preeclampsia is a medical emergency requiring hospitalization.^{6 7}

The cause of preeclampsia is unknown, although several factors have been shown to contribute.^{8 9} Preeclampsia has been found to be more common in women during their first pregnancy,¹⁰ and in women who are obese,^{11 12} diabetic,¹³ gestationally hypertensive,^{14 15 16} and who have had preeclampsia during a previous pregnancy.¹⁷ Preeclampsia has also been associated with calcium deficiencies,¹⁸ antioxidant deficiencies,^{19 20 21} older maternal age,²² and job stress.^{23 24 25}

Data from one preliminary trial suggest diets high in trans fatty acids are associated with an increased risk of preeclampsia.²⁸ Trans fatty acids are found in partially hydrogenated vegetable oils, such as margarine.

Job stress (lack of control over work pace and the timing and frequency of breaks) may be detrimental, and reducing it may be beneficial in the prevention of preeclampsia.²⁹ In a preliminary study, women exposed to high job stress were found to be at greater risk of developing preeclampsia and, to a lesser extent, gestational hypertension than were women exposed to low job stress. In this study, evaluation of job stress was based on scores assessing on-the-job psychological demand and decision-making latitude. High stress was defined as high psychological demand with low decision latitude, and low stress was defined as low demand, high latitude.³⁰

For women with preeclampsia, obstetricians and midwives recommend bed rest and lying on the left side; this position helps reduce edema and lower blood pressure by increasing urinary output.³¹

An analysis of double-blind studies⁴⁵ found calcium supplementation to be highly effective in preventing preeclampsia. However, a large and well-designed double-blind trial⁴⁶ and a critical analysis⁴⁷ of six double-blind studies^{48 49 50 51 52 53} concluded that calcium supplementation did not reduce the risk of preeclampsia in healthy women at low risk for preeclampsia. For healthy high-risk women, however, the data show a clear and statistically significant beneficial effect of calcium supplementation in reducing the risk of preeclampsia.⁵⁴

The National Institutes of Health recommends an intake of 1,200–1,500 mg of elemental calcium daily during normal pregnancy.^{55 56} In women at risk of preeclampsia, most studies showing reduced incidence have used 2,000 mg of supplemental calcium per day.⁵⁷ Nonetheless, many doctors continue to suggest amounts no higher than 1,500 mg per day.

Magnesium deficiency has been implicated as a possible cause of preeclampsia.^{58 59 60 61 62} Magnesium supplementation has been shown to reduce the incidence of preeclampsia in high-risk women in one study,⁶³ but not in another double-blind trial.⁶⁴

Recently, preeclamptic women have been shown to have elevated blood levels of homocysteine.^{65 66 67 68} Research indicates elevated homocysteine occurs prior to the onset of preeclampsia.⁶⁹ Elevated homocysteine damages the lining of blood vessels,^{70 71 72 73 74 75 76} which can lead to the preeclamptic signs of elevated blood pressure, swelling, and protein in the urine.⁷⁷

In one preliminary study, women with high homocysteine and a previous pregnancy complicated by preeclampsia, who supplemented with 5 mg of folic acid and 250 mg of vitamin B6 per day, successfully lowered homocysteine levels.⁷⁸ In another trial studying the effect of vitamin B6 on preeclampsia incidence, supplementation with 5 mg of vitamin B6 twice per day significantly reduced the incidence of preeclampsia. However, women were not evaluated for homocysteine levels in that study.⁷⁹ In fact, no studies have yet determined if lowering elevated homocysteine reduces the incidence or severity of preeclampsia.

Elevated homocysteine is also associated with the development of cardiovascular disease.⁸⁰ Furthermore, women with a history of preeclampsia are believed to be at greater risk of developing atherosclerosis in later years.^{81 82} Therefore, despite a lack of proof that elevated homocysteine levels cause preeclampsia, some doctors believe that until more is known, pregnant women with elevated homocysteine should attempt to reduce those levels to normal. Lowered homocysteine is achieved in most published reports by supplementation with folic acid, vitamin B12, and vitamin B6.^{83 84}

A marginal zinc deficiency has been reported in some women with preeclampsia.^{85 86} The common practice of prescribing iron and folic acid supplements to pregnant women can lead to reduced zinc absorption.⁸⁷

Trials studying the relationship between zinc supplementation and preeclampsia incidence have produced conflicting results. In one double-blind study, preeclampsia incidence was significantly lower in the group receiving 20 mg of zinc per day combined with a multivitamin-mineral supplement, compared to supplementation with the multivitamin-mineral preparation alone.⁸⁸ However, in another double-blind trial, a higher incidence of preeclampsia was reported in pregnant women given 20 mg of zinc per day than was reported in women given a placebo.⁸⁹ Therefore, current evidence does not sufficiently support the use of zinc as a way to protect against preeclampsia.

Preeclamptic patients have been found to be depleted in antioxidants.^{95 96} Some^{97 98} but not all studies⁹⁹ have reported deficiencies in antioxidant vitamins such as C, E, and beta-carotene in preeclampsia patients.

In a recent double-blind study, supplementation of vitamin C (one gram per day) and vitamin E (400 IU per day) reduced the incidence of preeclampsia in women at high risk.¹⁰⁰ However, for those already suffering from this condition, supplementation with these same vitamins has led to only insignificant effects.¹⁰¹

Information about the effects of a particular supplement or herb on a particular condition has been qualified in terms of the methodology or source of supporting data (for example: clinical, double blind, meta-analysis, or traditional use). For the convenience of the reader, the information in the table listing the supplements for particular conditions is also categorized. The criteria for the categorizations are: "Primary" indicates there are reliable and relatively consistent scientific data showing a health benefit. "Secondary" indicates there are conflicting, insufficient, or only preliminary studies suggesting a health benefit or that the health benefit is minimal. "Other" indicates that an herb is primarily supported by traditional use or that the herb or supplement has little scientific support and/or minimal proven health benefit.

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3. Rey E, LeLorier J, Burgess E, et al. Report of the Canadian Hypertension Society Consensus Conference: 3. Pharmacologic treatment of hypertensive disorders in pregnancy. CMAJ 1997;157:1245–54.

4. Rath W Z. [Treatment of hypertensive diseases in pregnancy—general recommendations and long-term oral therapy]. Geburtshilfe Neonatol 1997;201:240–6 [in German].

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6. Rey E, LeLorier J, Burgess E, et al. Report of the Canadian Hypertension Society Consensus Conference: 3. Pharmacologic treatment of hypertensive disorders in pregnancy. CMAJ 1997;157:1245–54.

7. Sibai BM, Frangieh AY. Management of severe preeclampsia. Curr Opin Obstet Gynecol 1996;8(2):110–3.

8. Myatt L, Miodovnik M. Prediction of preeclampsia. Semin Perinatol 1999;23:45–57.

9. Sibai B. Prevention of preeclampsia: a big disappointment. Am J Obstet Gynecol 1998;179:1275–8 [review].

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