|Classification and external resources|
Pre-eclampsia or preeclampsia is a disorder of pregnancy characterized by high blood pressure and large amounts of protein in the urine. Though present in the majority of cases, protein in the urine need not be present to make the diagnosis of preeclampsia. It involves many body systems and evidence of associated organ dysfunction may be used to make the diagnosis when hypertension is present. This includes the presence of a low blood platelet count (thrombocytopenia), impaired liver function, the development of new kidney dysfunction, fluid accumulation in the lungs (pulmonary edema), and/or new-onset brain or visual disturbances. If left untreated, preeclampsia can develop into eclampsia, the life-threatening occurrence of seizures during pregnancy. Preeclampsia is associated with multiple maternal and fetal adverse effects.
The cause and pathogenesis of preeclampsia has yet to be definitively uncovered, though the syndrome is almost certainly the result of multiple factors. It is now thought that abnormal placentation (development and arrangement of the placenta) and placental function is a strong predisposing factor for preeclampsia, though there are a host of contributing and related factors that complicate finding a precise mechanism for preeclampsia. These include immunologic, hematologic, genetic, and environmental factors. Central to the effects of preeclampsia are the resulting presence of uteroplacental hypoxia (inadequate oxygen supply), an imbalance in angiogenic and anti-angiogenic proteins, oxidative stress, maternal endothelial (lining of blood vessels) dysfunction, and elevated systemic inflammation. Given the syndromic and mulitfactorial nature of the disease, it is not yet possible to routinely predict preeclampsia.
Preeclampsia affects between 2-8% of pregnancies worldwide. It may develop after 20 weeks of gestation, though most commonly after 32 weeks. Preeclampsia occurring before 32 weeks is considered early-onset and is associated with increased morbidity. Most cases are diagnosed before the predicted time typical labor would begin. Delivery of the fetus and placenta is the only known treatment for preeclampsia. Rarely, preeclampsia may also occur in the postpartum period.
- 1 Signs and symptoms
- 2 Causes
- 3 Pathogenesis
- 4 Diagnosis
- 5 Prevention
- 6 Management
- 7 Epidemiology
- 8 Complications
- 9 Research
- 10 References
- 11 External links
Signs and symptoms
Swelling or edema (especially in the hands and face) was originally considered an important sign for a diagnosis of preeclampsia. However, because swelling is a common occurrence in pregnancy, its utility as a distinguishing factor in preeclampsia is not great. Pitting edema (unusual swelling, particularly of the hands, feet, or face, notable by leaving an indentation when pressed on) can be significant, and should be reported to a health care provider.
In general, none of the signs of preeclampsia are specific, and even convulsions in pregnancy are more likely to have causes other than eclampsia in modern practice. Further, a symptom such as epigastric pain may be misinterpreted as heartburn. Diagnosis, therefore, depends on finding a coincidence of several preeclamptic features, the final proof being their regression after delivery.
- abnormal placentation (formation and development of the placenta)
- Immunologic factors
- Prior or existing maternal pathology - preeclampsia is seen more at a higher incidence in individuals with preexisting hypertension, obesity, antiphospholipid antibody syndrome, and those with history of preeclampsia
- Dietary factors, e.g. calcium supplementation in areas where dietary calcium intake is low has been shown to reduce the risk of preeclampsia
- Environmental factors, e.g. air pollution
Physiologically, research has linked preeclampsia to the following physiologic changes: alterations in the interaction between the maternal immune response and the placenta, placental injury, endothelial cell injury, altered vascular reactivity, oxidative stress, imbalance among vasoactive substances, decreased intravascular volume, and disseminated intravascular coagulation.
While the exact cause of preeclampsia remains unclear, there is strong evidence that a major cause predisposing a susceptible woman to preeclampsia is an abnormally implanted placenta. This abnormally implanted placenta is thought to result in poor uterine and placental perfusion, yielding a state of hypoxia and increased oxidative stress and the release of anti-angiogenic proteins into the maternal plasma along with inflammatory mediators. A major consequence of all this is generalized endothelial dysfunction. The abnormal implantation is thought to stem from the maternal immune system's response to the placenta and refers to evidence suggesting a lack of established immunological tolerance in pregnancy. Endothelial dysfunction results in hypertension and many of the other symptoms and complications associated with preclampsia.
- Nulliparity (never given birth)
- Diabetes mellitus
- Renal disease
- Chronic hypertension
- Prior history of preeclampsia
- Family history of preeclampsia
- Advanced maternal age (>35 years)
- Antiphospholipid antibody syndrome
- Multiple gestation
Although much research into mechanism of preeclampsia has taken place, its exact pathogenesis remains uncertain. Preeclampsia is thought to result from an abnormal placenta, the removal of which ends the disease in most cases. During normal pregnancy, the placenta undergoes process of vascularization to allow for blood flow between the mother and fetus. Abnormal development of the placenta leads to poor placental perfusion. The placenta of women with preeclampsia is abnormal and characterized by poor trophoblastic invasion. It is thought that this results in oxidative stress, hypoxia, and release of factors that promote endothelial dysfunction, inflammation, and other possible reactions.
The clinical manifestations of preeclampsia are associated with general endothelial dysfunction, including vasoconstriction and end-organ ischemia. Implicit in this generalized endothelial dysfunction may be an imbalance of angiogenic and anti-angiogenic factors. Both circulating and placental levels of soluble fms-like tyrosine kinase-1 (sFlt-1) are higher in women with preeclampsia than in women with normal pregnancy. sFlt-1 is an anti-angiogenic protein that antagonizes vascular endothelial growth factor (VEGF) and placental growth factor (PIGF), both of with are proangiogenic factors. Soluble endoglin (sEng) has also been shown to be elevated in women with preeclampsia and has anti-angiogenic properties, much like sFlt-1 does.
Both sFlt-1 and sEng are upregulated in all pregnant women to some extent, supporting the idea that hypertensive disease in pregnancy is a normal pregnancy adaptation gone awry. As natural killer cells are intimately involved in placentation and as placentation involves a degree of maternal immune tolerance for a foreign placenta which requires maternal resources for its support, it is not surprising that the maternal immune system might respond more negatively to the arrival of some placentae under certain circumstances, such as a placenta which is more invasive than normal. Initial maternal rejection of the placental cytotrophoblasts may be the cause of the inadequately remodeled spiral arteries in those cases of pre-eclampsia associated with shallow implantation, leading to downstream hypoxia and the appearance of maternal symptoms in response to upregulated sFlt-1 and sEng.
Oxidative stress is thought to play an important part in the pathogensis of pre-eclampsia. The main souce of reactive oxygen species (ROS) is the enzyme xanthine oxidase (XO) and this enzyme mainly occurs in the liver. One hypothesis is that the increased purine catabolism from placental hypoxia results in increased ROS production in the maternal liver and release into the maternal circulation causing endothelial cell damage.
Abnormalities in the maternal immune system and insufficiency of gestational immune tolerance seem to play major roles in pre-eclampsia. One of the main differences found in pre-eclampsia is a shift toward Th1 responses and the production of IFN-γ. The origin of IFN-γ is not clearly identified and could be the natural killer cells of the uterus, the placental dendritic cells modulating responses of T helper cells, alterations in synthesis of or response to regulatory molecules, or changes in the function of regulatory T cells in pregnancy. Aberrant immune responses promoting pre-eclampsia may also be due to an altered fetal allorecognition or to inflammatory triggers. It has been documented that fetal cells such as fetal erythroblasts as well as cell-free fetal DNA are increased in the maternal circulation in women who develop pre-eclampsia. These findings have given rise to the hypothesis that pre-eclampsia is a disease process by which a placental lesion such as hypoxia allows increased fetal material into maternal circulation that leads to an immune response and endothelial damage ultimately resulting in pre-eclampsia and eclampsia.
One hypothesis for vulnerability to preeclampsia is the maternal-fetal conflict between the maternal organism and fetus. After the first trimester trophoblasts enter the spiral arteries of the mother to alter the spiral arteries and thereby gain more access to maternal nutrients. However, occasionally there is impaired trophoblast invasion that results in inadequate alterations to the uterine spiral arteries. It is hypothesized that the developing embryo releases biochemical signals that result in the woman developing hypertension and preeclampsia so that the fetus can benefit from a greater amount of maternal circulation of nutrients due to increased blood flow to the impaired placenta. This results in a conflict between the maternal organism’s Darwinian fitness and survival and the developing fetus because the fetus is invested in only its survival and fitness while the mother is invested in this pregnancy and subsequent potential pregnancies.
Another evolutionary hypothesis for vulnerability to preeclampsia is the idea of ensuring pair-bonding between the mother and father and paternal investment in the fetus. Researchers posit the idea that preeclampsia serves as an adaptation for the mother to terminate investment in a fetus that might have an unavailable paternal donor, as determined by repeated semen exposure of the paternal donor to the mother. Various studies have shown that women who frequently had exposure to partners’ semen before conception had a reduced risk of preeclampsia. Also, subsequent pregnancies by the same paternal donor had a reduced risk of preeclampsia while subsequent pregnancies by a different paternal donor had a higher risk of developing preeclampsia.
- Blood pressure ≥ 140 mm Hg systolic or ≥ 90 mm Hg diastolic on two separate readings taken at least four to six hours apart after 20 weeks gestation in an individual with previously normal blood pressure.
- Proteinuria ≥ 0.3 grams (300 mg) or more of protein in a 24-hour urine sample or a SPOT urinary protein to creatinine ratio ≥ 0.3 or a urine dipstick reading of 1+ or greater (dipstick reading should only be used if other quantitative methods are not available).
Suspicion for preeclampsia should be maintained in any pregnancy complicated by elevated blood pressure, even in the absence of proteinuria. Ten percent of individuals with other signs and symptoms of preeclampsia and 20% of individuals diagnosed with eclampsia show no evidence of proteinuria. In the absence of proteinuria, the presence of new-onset hypertension (elevated blood pressure) and the new onset of one or more of the following is suggestive of the diagnosis of preeclampsia:
- Evidence of kidney dysfunction (oliguria, elevated creatinine levels)
- Impaired liver function (impaired liver function tests)
- Thrombocytopenia (platelet count <100,000/microliter)
- Pulmonary edema
- Ankle edema pitting type
- Cerebral or visual disturbances
Preeclampsia is a progressive disorder and these signs of organ dysfunction are indicative of severe preeclampsia. A systolic blood pressure ≥160 or diastolic blood pressure ≥110 and/or proteinuria >5g in a 24-hour period is also indicative of severe preeclampsia. Clinically, individuals with severe preeclampsia may also present epigastric/right upper quadrant abdominal pain, headaches, and vomiting. Severe preeclampsia is a significant risk factor for intrauterine fetal death.
Of note, a rise in baseline blood pressure (BP) of 30 mmHg systolic or 15 mmHg diastolic, while not meeting the absolute criteria of 140/90, is still considered important to note, but is not considered diagnostic.
There have been many assessments of tests aimed at predicting preeclampsia, though no single biomarker is likely to be sufficiently predictive of the disorder. Predictive tests that have been assessed include those related to placental perfusion, vascular resistance, kidney dysfunction, endothelial dysfunction, and oxidative stress. Examples of notable tests include:
- Doppler ultrasonography of the uterine arteries to investigate for signs of inadequate placental perfusion. This test has a high negative predictive value among those individuals with a history of prior preeclampsia.
- Elevations in serum uric acid (hyperuricemia) is used by some to “define” preeclampsia, though it has been found to be a poor predictor of the disorder. Elevated levels in the blood (hyperuricemia) are likely due to reduced uric acid clearance secondary to impaired kidney function.
- Angiogenic proteins such as vascular endothelial growth factor (VEGF) and placental growth factor (PIGF) and anti-angiogenic proteins such as soluble fms-like tyrosine kinase-1 (sFlt-1) have shown promise for potential clinical use in diagnosing preeclampsia, though evidence is sufficient to recommend a clinical use for these markers.
- Recent studies have shown that looking for podocytes, specialized cells of the kidney, in the urine has the potential to aid in the prediction of preeclampsia. Studies have demonstrated that finding podocytes in the urine may serve as an early marker of and diagnostic test for preeclampsia. Research is ongoing.
Pre-eclampsia can mimic and be confused with many other diseases, including chronic hypertension, chronic renal disease, primary seizure disorders, gallbladder and pancreatic disease, immune or thrombotic thrombocytopenic purpura, antiphospholipid syndrome and hemolytic-uremic syndrome. It must always be considered a possibility in any pregnant woman beyond 20 weeks of gestation. It is particularly difficult to diagnose when preexisting disease such as hypertension is present. Women with acute fatty liver of pregnancy may also present with elevated blood pressure and protein in the urine, but differs by the extent of liver damage.
Preventative measures against preeclampsia have been heavily studied. Because the pathogensis of preeclampsia is not completely understood, prevention remains a complex issue. Below are some of the currently accepted recommendations.
Protein or calorie supplementation have no effect on preeclampsia rates, and dietary protein restriction does not appear to increase preeclampsia rates. Further, there is no evidence that changing salt intake has an effect.
Supplementation with antioxidants such as vitamin C and E has no effect on preeclampsia incidence, nor does supplementation with vitamin D. Therefore, supplementation with vitamins C, E, and D is not recommended.
Calcium supplementation of at least 1 gram per day is recommended during pregnancy as it prevents preeclampsia where dietary calcium intake is low, especially for those at high risk. Low selenium status is associated with higher incidence of preeclampsia.
Taking aspirin is associated with a 1% to 5% reduction in preeclampsia and a 1% to 5% reduction in premature births in women at high risk. The WHO recommends low-dose aspirin for the prevention of preeclampsia in women at high risk and recommend it be started before 20 weeks of pregnancy. The United States Preventive Services Task Force recommends a low-dose regimen for women at high risk beginning in the 12th week.
In low-risk pregnancies the association between cigarette smoking and a reduced risk of preeclampsia has been consistent and reproducible across epidemiologic studies. High-risk pregnancies (those with pregestational diabetes, chronic hypertension, history of preeclampsia in a previous pregnancy, or multifetal gestation) showed no significant protective effect. The reason for this discrepancy is not definitively known; research supports speculation that the underlying pathology increases the risk of preeclampsia to such a degree that any measurable reduction of risk due to smoking is masked. However, the damaging effects of smoking on overall health and pregnancy outcomes outweighs the benefits in decreasing the incidence of preeclampsia. It is recommended that smoking be stopped prior to, during and after pregnancy.
The only known definitive treatment for preeclampsia is delivery of the fetus and placenta. The timing of delivery should balance the desire for optimal perinatal outcomes for the fetus while reducing maternal risks. The severity of disease and the maturity of the fetus are primary considerations. These considerations are situation-specific and management will vary with situation, location, and institution. Treatment can range from expectant management to expedited delivery of the fetus and placenta by induction of labor or Caesarian section, in addition to pharmaceutical interventions. Important in management is the assessment of vulnerable maternal organ systems when possible, management of severe hypertension, and prevention and treatment of eclamptic seizures. Separate interventions directed at the fetus may also be necessary.
The WHO recommends that women with severe hypertension during pregnancy should receive treatment with anti-hypertensive agents. Severe hypertension is generally considered systolic BP of at least 160 or diastolic BP of at least 110. Evidence does not support the use of one anti-hypertensive over another. The choice of which agent to use should be based on the prescribing clinician's experience with a particular agent, its cost, and its availability. Diuretics are not recommended for prevention of preeclampsia and its complications. Labetolol, Hydralazine and Nifedipine are commonly used antihypertensive agents for hypertension in pregnancy. ACE inhibitors and angiotensin receptor blockers are contraindicated as they affect fetal development.
The goal of treatment of severe hypertension in pregnancy is to prevent cardiovascular, kidney, and cerebrovascular complications. The target blood pressure has been proposed to be 140-160 mmHg systolic and 90-105 mmHg diastolic, although values are variable.
Prevention of eclampsia
The intrapartum and postpartum administration of magnesium sulfate is recommended in severe preeclampsia for the prevention of eclampsia. Further, magnesium sulfate is recommended for the treatment of eclampsia over other anticonvulsants. Magnesium sulfate acts by interacting with NMDA receptors. Evidence for the use of magnesium sulfate came from the international MAGPIE study.
Pre-eclampsia affects approximately 2-8% of all pregnancies worldwide, with onset of symptoms in the late second or third trimester, most commonly after the 32nd week. Some women will experience preeclampsia as early as 20 weeks, though this is rare. Preeclampsia may also occur in the immediate postpartum period.
Preeclampsia is one of the leading causes of maternal and perinatal morbidity and mortality worldwide. Nearly one tenth of all maternal deaths in Africa and Asia and one quarter in Latin America are associated with hypertensive diseases in pregnancy, a category that encompasses preeclampsia.
Preeclampsia is much more common in women who are pregnant for the first time and in women who have previously been diagosed with preeclampsia. Pre-eclampsia is also more common in women who have preexisting hypertension, diabetes, autoimmune diseases such as lupus, various inherited thrombophilias such as Factor V Leiden, renal disease, women with a family history of pre-eclampsia, obese women, women with a multiple gestation (twins or multiple birth), and women of advanced maternal age. Change of paternity in a subsequent pregnancy has also been implicated as affecting risk, except in those with a family history of hypertensive pregnancy
Eclampsia is a major complication of preeclampsia. Eclampsia affects 0.56 per 1000 pregnant women in developed countries and almost 10-30 times as many women in low-income countries as in developed countries.
Complications of preeclampsia can affect both the mother and the fetus. Acutely, preeclampsia can be complicated by eclampsia, the development of HELLP syndrome, hemorrhagic or ischemic stroke, liver damage and dysfunction, acute kidney injury, and acute respiratory distress syndrome (ARDS).
Preeclampsia is also associated with increased frequency of Caesarian section, preterm delivery, and placental abruption. Furthermore, an elevation in blood pressure can occur in some individuals in the first week postpartum attributable to volume expansion and fluid mobilization. Fetal complications include fetal growth restriction and a potentially fetal or perinatal death.
Long-term, an individual with preeclampsia is at increased risk for recurrence of preeclampsia in subsequent pregnancies. There is also an increased risk for cardiovascular complications, including hypertension and ischemic heart disease, and kidney disease.
Eclampsia is the development of new convulsions in a preeclamptic patient that may not be attributed to other cause. Eclampsia is a serious complication of preeclampsia and results in high rates of perinatal and maternal morbidity and mortality. Warning symptoms for eclampsia in an individual with current preeclampsia may include headaches, visual disturbances, and right upper quadrant or epigastric abdominal pain, with headache being the most consistent symptom. Magnesium sulfate is used to prevent convulsions in cases of severe preeclampsia.
HELLP syndrome is defined as hemolysis (microangiopathic), elevated liver enzymes (liver dysfunction), and low platelets (thrombocytopenia). This condition may occur in 10-20% of patients with severe preeclampsia and eclampsia and is associated with increased maternal and fetal morbidity and mortality. In 50% of instances, HELLP syndrome develops preterm, while 20% of cases develop in late gestation and 30% during the post-partum period.
Many studies have also suggested the importance of a woman's immunological tolerance to her baby's father, whose genes are present in the young fetus and its placenta and which may pose a challenge to her immune system. As the theory is further investigated, researchers are increasingly studying the importance of a woman's continued exposure to her partner's semen as early as several years before conception. One study published in the American Journal of Obstetrics and Gynecology involved several hundreds of women and found that "women with a short period of cohabitation (less than 4 months) who used barrier methods for contraception had a substantially elevated risk for the development of pre-eclampsia compared with women with more than 12 months of cohabitation before conception". However, the results from a study conducted in 2004 show that the theory is still not conclusive. In that study, the researchers found that after adjustment and stratification, the effect of barrier contraceptive use on the development of pre-eclampsia had disappeared, with both arms having identical rates of pre-eclampsia. Although the study has since been criticized for its subjective adjustment of data, it remains important because it demonstrates that there is still some contention over the degree to which failure of tolerance induction can be attributed to prior exposure to the partner's sperm.
Long periods of sexual cohabitation with the same partner fathering a woman's child significantly decreased her chances of suffering pre-eclampsia. As one early study described, "although pre-eclampsia is a disease of first pregnancies, the protective effect of multiparity is lost with change of partner". The study also concluded that although women with changing partners are strongly advised to use condoms to prevent sexually transmitted diseases, "a certain period of sperm exposure within a stable relation, when pregnancy is aimed for, is associated with protection against pre-eclampsia".
Several other studies have since investigated the strongly decreased incidence of pre-eclampsia in women who had received blood transfusions from their partner, those with long, preceding histories of sex without barrier contraceptives, and in women who had been regularly performing oral sex, with one study concluding "induction of allogeneic tolerance to the paternal human leukocyte antigen (HLA) molecules of the fetus may be crucial. Data collected strongly suggest that exposure, and especially oral exposure to soluble HLA from semen can lead to transplantation tolerance."
According to the theory, the fetus and placenta both contain "foreign" proteins from paternal genes, but regular, preceding and coincident exposure to the father's semen may promote immune acceptance and subsequent implantation, a process which is significantly supported by as many as 93 currently identified immune regulating factors in seminal fluid.
Having already noted the importance of a woman's immunological tolerance to her baby's paternal genes, several Dutch reproductive biologists decided to take their research a step further. Consistent with the fact that human immune systems tolerate things better when they enter the body via the mouth, the Dutch researchers conducted a series of studies that confirmed a surprisingly strong correlation between a diminished incidence of pre-eclampsia and a woman's practice of oral sex, and noted that the protective effects were strongest if she swallowed her partner's semen. The researchers concluded that while any exposure to a partner's semen during sexual activity appears to decrease a woman's chances for the various immunological disorders that can occur during pregnancy, immunological tolerance could be most quickly established through oral introduction and gastrointestinal absorption of semen. Recognizing that some of the studies potentially included the presence of confounding factors, such as the possibility that women who regularly perform oral sex and swallow semen also engage in more frequent intercourse, the researchers also noted that, either way, "the data still overwhelmingly supports the main theory" behind all their studies—that repeated exposure to semen establishes the maternal immunological tolerance necessary for a safe and successful pregnancy.
A team from the University of Adelaide has also investigated to see if men who have fathered pregnancies which have ended in miscarriage or pre-eclampsia had low seminal levels of critical immune modulating factors such as TGF-Beta. The team has found that certain men, dubbed "dangerous males", are several times more likely to father pregnancies that would end in either pre-eclampsia or miscarriage. Among other things, most of the "dangerous males" seemed to lack sufficient levels of the seminal immune factors necessary to induce immunological tolerance in their partners.
As the theory of immune intolerance as a cause of pre-eclampsia has become accepted, women who with repeated pre-eclampsia, miscarriages, or In Vitro Fertilization failures could potentially be administered key immune factors such as TGF-beta along with the father's foreign proteins, possibly either orally, as a sublingual spray, or as a vaginal gel to be applied onto the vaginal wall before intercourse.
It was reported that patients with pre-eclampsia have higher levels of endothelial microparticles than healthy controls. Concentration of endothelial microparticles has been proposed as a biomarker for pre-eclampsia severity.
- Pregnancy, developed by the Task Force on Hypertension in (2013). Hypertension in pregnancy. ISBN 978-1-934984-28-4.
- Eiland, Elosha; Nzerue, Chike; Faulkner, Marquetta (2012). "Preeclampsia 2012". Journal of Pregnancy 2012: 1–7. doi:10.1155/2012/586578.
- Steegers, Eric AP; von Dadelszen, Peter; Duvekot, Johannes J; Pijnenborg, Robert (August 2010). "Pre-eclampsia". The Lancet 376 (9741): 631–644. doi:10.1016/S0140-6736(10)60279-6.
- Al-Jameil (2013). "A Brief Overview of Preeclampsia". Journal of Clinical Medicine Research. doi:10.4021/jocmr1682w.
- WHO recommendations for prevention and treatment of pre-eclampsia and eclampsia. 2011. ISBN 978-92-4-154833-5.
- Lisonkova, S; Joseph, KS (Dec 2013). "Incidence of preeclampsia: risk factors and outcomes associated with early- versus late-onset disease.". American journal of obstetrics and gynecology 209 (6): 544.e1–544.e12. doi:10.1016/j.ajog.2013.08.019. PMID 23973398.
- Arulkumaran, N.; Lightstone, L. (December 2013). "Severe pre-eclampsia and hypertensive crises". Best Practice & Research Clinical Obstetrics & Gynaecology 27 (6): 877–884. doi:10.1016/j.bpobgyn.2013.07.003.
- "Hypertension- Validations - Pregnancy". microlife.com.
- Jun Wu, Cizao Ren, Ralph J. Delfino, Judith Chung, Michelle Wilhelm, & Beate Ritz (2009). "Association Between Local Traffic-Generated Air Pollution and Pre-eclampsia and Preterm Delivery in the South Coast Air Basin of California". Environmental Health Perspectives. Retrieved 2009-07-05.
- Bramham, K; Parnell, B; Nelson-Piercy, C; Seed, PT; Poston, L; Chappell, LC (Apr 15, 2014). "Chronic hypertension and pregnancy outcomes: systematic review and meta-analysis.". BMJ (Clinical research ed.) 348: g2301. doi:10.1136/bmj.g2301. PMC 3988319. PMID 24735917.
- Mustafa, Reem; Ahmed, Sana; Gupta, Anu; Venuto, Rocco C. (2012). "A Comprehensive Review of Hypertension in Pregnancy". Journal of Pregnancy 2012: 1–19. doi:10.1155/2012/105918.
- al.], [edited by] F. Gary Cunningham ... [et (2010). Williams obstetrics. (23rd ed. ed.). New York: McGraw-Hill Medical. ISBN 978-0-07-149701-5.
- Drife, James O.; Magowan, Brian. (2004). Clinical obstetrics and gynecology. Edinburgh ; New York: Saunders. pp. 367–370. ISBN 0-7020-1775-2.
- McMaster-Fay RA (2008). "Pre-eclampsia: a disease of oxidative stress resulting from the catabolism of DNA (primarily fetal) to uric acid by xanthine oxidase in the maternal liver; a hypothesis.". Bioscience Hypotheses 1: 35–43. doi:10.1016/j.bihy.2008.01.002.
- Laresgoiti-Servitje E, Gómez-López N, Olson DM (April 2010). "An immunological insight into the origins of pre-eclampsia". Hum Reprod Update 16 (5): 510–24. doi:10.1093/humupd/dmq007. PMID 20388637.
- Redman CW, Sargent IL (2005). "Latest Advances in Understanding Preeclampsia". Science 308 (5728): 1592–1594. doi:10.1126/science.1111726. PMID 15947178.
- Davis, J. A.; Gallup, G. G. J. (2006). "Preeclampsia and other pregnancy complications as an adaptive response to unfamiliar semen". In Platek, Steven M; Shackelford, Todd K. "Female Infidelity and Paternal Uncertainty". p. 191. doi:10.1017/CBO9780511617812.010. ISBN 9780511617812.
- Longo, Dan L. (Dan Louis) (2012). Harrison's principles of internal medicine. New York: McGraw-Hill. pp. 55–61. ISBN 978-0-07-174889-6.
- Craici, IM; Wagner, SJ; Bailey, KR; Fitz-Gibbon, PD; Wood-Wentz, CM; Turner, ST; Hayman, SR; White, WM; Brost, BC; Rose, CH; Grande, JP; Garovic, VD (Jun 2013). "Podocyturia predates proteinuria and clinical features of preeclampsia: longitudinal prospective study.". Hypertension 61 (6): 1289–96. doi:10.1161/HYPERTENSIONAHA.113.01115. PMC 3713793. PMID 23529165.
- "BBC News - Pre-eclampsia predicted using test during pregnancy". 2011-11-12. Retrieved 2011-11-22.
- "Mechanisms and Management of Hypertension in Pregnant Women.". Retrieved 2011-11-22.
- "Pre-eclampsia-Eclampsia". Diagnosis and management of pre-eclampsia and eclampsia. Armenian Medical Network. 2003. Retrieved 2005-11-23.
- Kramer MS, Kakuma R (2003). Kramer, Michael S, ed. "Energy and protein intake in pregnancy". Cochrane Database of Systematic Reviews (4): CD000032. doi:10.1002/14651858.CD000032. PMID 14583907.
- Duley L, Henderson-Smart D, Meher S (Oct 19, 2005). "Altered dietary salt for preventing pre-eclampsia, and its complications.". The Cochrane database of systematic reviews (4): CD005548. doi:10.1002/14651858.CD005548. PMID 16235411.
- Rumbold AR, Crowther CA, Haslam RR, Dekker GA, Robinson JS (April 2006). "Vitamins C and E and the risks of pre-eclampsia and perinatal complications". The New England Journal of Medicine 354 (17): 1796–806. doi:10.1056/NEJMoa054186. PMID 16641396.
- WHO recommendations for prevention and treatment of pre-eclampsia and eclampsia. 2011. ISBN 978-92-4-154833-5.
- Hofmeyr, GJ; Lawrie, TA; Atallah, AN; Duley, L; Torloni, MR (Jun 24, 2014). "Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems.". The Cochrane database of systematic reviews 6: CD001059. doi:10.1002/14651858.CD001059.pub4. PMID 24960615.
- Rayman MP, Bode P, Redman CW (November 2003). "Low selenium status is associated with the occurrence of the pregnancy disease pre-eclampsia in women from the United Kingdom". American Journal of Obstetrics and Gynecology 189 (5): 1343–9. doi:10.1067/S0002-9378(03)00723-3. PMID 14634566.
- Henderson, JT; Whitlock, EP; O'Connor, E; Senger, CA; Thompson, JH; Rowland, MG (May 20, 2014). "Low-dose aspirin for prevention of morbidity and mortality from preeclampsia: a systematic evidence review for the U.S. Preventive Services Task Force.". Annals of internal medicine 160 (10): 695–703. doi:10.7326/M13-2844. PMID 24711050.
- Duley L, Henderson-Smart DJ, Meher S, King JF (2007). "Antiplatelet agents for preventing pre-eclampsia and its complications". Cochrane Database Syst Rev (2): CD004659. doi:10.1002/14651858.CD004659.pub2. PMID 17443552.
- "Low-Dose Aspirin Use for the Prevention of Morbidity and Mortality From Preeclampsia". United States Preventive Services Task Force. Sep 2014. Retrieved 17 Sep 2014.
- Meher S, Duley L (2006). Meher, Shireen, ed. "Exercise or other physical activity for preventing pre-eclampsia and its complications". Cochrane Database of Systematic Reviews (2): CD005942. doi:10.1002/14651858.CD005942. PMID 16625645.
- Meher S, Duley L (2006). Meher, Shireen, ed. "Rest during pregnancy for preventing pre-eclampsia and its complications in women with normal blood pressure". Cochrane Database of Systematic Reviews (2): CD005939. doi:10.1002/14651858.CD005939. PMID 16625644.
- Jeyabalan A, Powers RW, Durica AR, Harger GF, Roberts JM, Ness RB (August 2008). "Cigarette Smoke Exposure and Angiogenic Factors in Pregnancy and Preeclampsia". Am. J. Hypertens. 21 (8): 943–7. doi:10.1038/ajh.2008.219. PMC 2613772. PMID 18566591.
- Whitworth, M; Dowswell, T (Oct 7, 2009). "Routine pre-pregnancy health promotion for improving pregnancy outcomes.". The Cochrane database of systematic reviews (4): CD007536. doi:10.1002/14651858.CD007536.pub2. PMID 19821424.
- Obstetrics, Charles R.B. Beckmann ... [et al.] ; American College of; (ACOG), Gynecology (2010). Obstetrics and gynecology. (6th ed. ed.). Baltimore, MD: Lippincott Williams & Wilkins. ISBN 0781788072.
- Hypertensive Disorders in Pregnancy. Version 2.0. at Nederlandse Vereniging voor Obstetrie en Gynaecologie. Date of approval: 20-05-2005
- "The Magpie Trial follow up study: outcome after discharge from hospital for women and children recruited to a trial comparing magnesium sulphate with placebo for pre-eclampsia ISRCTN86938761". BMC Pregnancy and Childbirth 4 (1): 5. March 2004. doi:10.1186/1471-2393-4-5. PMC 416479. PMID 15113445.
- World Health Organization (WHO). World health report 2005: make every mother and child count. Geneva: WHO; 2005, page 63
- Robbins and Cotran, Pathological Basis of Disease, 7th ed.
- Hjartardottir S, Leifsson BG, Geirsson RT, Steinthorsdottir V (2004). "Paternity change and the recurrence risk in familial hypertensive disorder in pregnancy". Hypertension in Pregnancy 23 (2): 219–25. doi:10.1081/PRG-120037889. PMID 15369654.
- al.], [edited by] F. Gary Cunningham ... [et (2010). Williams obstetrics. (23rd ed. ed.). New York: McGraw-Hill Medical. ISBN 978-0071497015.
- Burne, Jerome (2006-01-30). "Give Sperm a Fighting Chance". The Times. Retrieved 2007-11-16.[dead link]
- "Sex Primes Women for Sperm". BBC News. 2002-02-06. Retrieved 2007-11-19.
- Waite LL, Atwood AK, Taylor RN (May 2002). "Pre-eclampsia, an implantation disorder". Reviews in Endocrine & Metabolic Disorders 3 (2): 151–8. doi:10.1023/A:1015411113468. PMID 12007292.
- Einarsson JI, Sangi-Haghpeykar H, Gardner MO (May 2003). "Sperm exposure and development of pre-eclampsia". American Journal of Obstetrics and Gynecology 188 (5): 1241–3. doi:10.1067/mob.2003.401. PMID 12748491.
- Ness RB, Markovic N, Harger G, Day R (2004). "Barrier methods, length of preconception intercourse, and pre-eclampsia". Hypertension in Pregnancy 23 (3): 227–35. doi:10.1081/PRG-200030293. PMID 15617622.
- Sarah Robertson. "Research Goals --> Role of seminal fluid signalling in the female reproductive tract".
- Robertson SA, Bromfield JJ, Tremellen KP (August 2003). "Seminal 'priming' for protection from pre-eclampsia-a unifying hypothesis". Journal of Reproductive Immunology 59 (2): 253–65. doi:10.1016/S0165-0378(03)00052-4. PMID 12896827.
- Dekker GA, Robillard PY, Hulsey TC (June 1998). "Immune maladaptation in the etiology of pre-eclampsia: a review of corroborative epidemiologic studies". Obstetrical & Gynecological Survey 53 (6): 377–82. doi:10.1097/00006254-199806000-00023. PMID 9618714.
- Bonney EA (December 2007). "Preeclampsia: A view through the danger model". Journal of Reproductive Immunology 76 (1–2): 68–74. doi:10.1016/j.jri.2007.03.006. PMC 2246056. PMID 17482268.
- Koelman CA, Coumans AB, Nijman HW, Doxiadis II, Dekker GA, Claas FH (March 2000). "Correlation between oral sex and a low incidence of pre-eclampsia: a role for soluble HLA in seminal fluid?". Journal of Reproductive Immunology 46 (2): 155–66. doi:10.1016/S0165-0378(99)00062-5. PMID 10706945.
- Fox, Douglas (2002-02-09). "Gentle Persuasion". The New Scientist. Retrieved 2007-06-17.
- Mattar R, Soares RV, Daher S (February 2005). "Sexual behavior and recurrent spontaneous abortion". International Journal of Gynaecology and Obstetrics 88 (2): 154–5. doi:10.1016/j.ijgo.2004.11.006. PMID 15694097.
- Danielle Cavallucci, and Yvonne K. Fulbright (2008). Your Orgasmic Pregnancy. Alameda, CA: Hunter House Inc. Publishers. p. 90. ISBN 0897935012. http://books.google.com/books?id=othN_A1w2BYC&pg=PA90&lpg=PA90
- Jelto Drenth (2005). The Origin of the World. London: Reaktion Books. pp. 114–115. ISBN 1861892101.
- Dekker G (2002). "The partner's role in the etiology of pre-eclampsia". Journal of Reproductive Immunology 57 (1–2): 203–15. doi:10.1016/S0165-0378(02)00039-6. PMID 12385843.
- Ling L, Huang H, Zhu L, Mao T, Shen Q, Zhang H (Feb 2014). "Evaluation of plasma endothelial microparticles in pre-eclampsia.". J Int Med Res 42 (1): 42–51. doi:10.1177/0300060513504362. PMID 24319051.
- MedlinePlus entry on high blood pressure in pregnancy
- Mayo Clinic fact sheet on pre-eclampsia
- "Preeclampsia Research at the NICHD". NICHD : US Department of Health and Human Services & National Institutes of Health.