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Epidemiology of Hypertensive Disorders in Pregnancy
Editor's comment: Preeclampsia–eclampsia is a leading cause of maternal mortality and morbidity. Eclampsia has decreased dramatically in the last several decades in high-resource countries, probably reflecting improvements in medical care rather than a change in the disease's natural history. Conversely, preeclampsia's frequency is increasing in the United States (25% between 1987 and 2004 and 21% between 2005 and 2014 ), although it may be decreasing in other high-resource countries . The pregnancy-specific risk for preeclampsia is increased in women with nulliparity, multiple gestation, hydrops fetalis, and hydatidiform mole. Demographic and medical factors associated with an increased risk include elevated prepregnancy or early pregnancy blood pressure, prepregnancy adiposity and/or overweight or obesity, older age, family history, non-Hispanic Black race, and preexisting medical conditions ( e.g., chronic hypertension or diabetes). Each of these risk factors also increases the risk of future cardiovascular disease. This is consistent with the increased risk for cardiovascular disease being the highest in women with a history of preterm or recurrent preeclampsia. The current authors thank Roberta Ness for her prior contributions to this important Chapter.
Introduction
Hypertensive disorders specific to pregnancy include gestational hypertension, preeclampsia, and eclampsia. These syndromes, marked by elevations in blood pressure that arise at or after 20 weeks gestation and return to normal after delivery, are distinguished clinically by the presence or absence of proteinuria or other end-organ signs and symptoms. Eclampsia, derived from the Greek word for “lightning,” is a more life-threatening syndrome, characterized by seizures and thought to represent the progression of preeclampsia (“before the lightning”). Preeclampsia arising in the context of preexisting chronic hypertension is known as superimposed preeclampsia; in this case, blood pressure levels often do not return to normal after pregnancy. As many women's blood pressures are unknown before pregnancy, when hypertension fails to resolve after pregnancy, preexisting chronic hypertension with superimposed preeclampsia is assumed post hoc .
Here, we will review the epidemiologic data that characterize the occurrence, risk factors, predictors, natural history, and molecular epidemiology of hypertensive disorders of pregnancy. The purpose of this chapter is to review these epidemiologic data, critically assess the methods used in conducting previous studies, and suggest new research areas, focusing on preeclampsia. We will review evidence suggesting that preeclampsia, in itself, is a syndrome secondary to multiple pathophysiological pathways. We will discuss the natural heterogeneity among risk factors and clinical predictors, as well as among the outcomes for mothers and infants within the spectrum of preeclampsia.
Diagnostic Criteria and Research Definitions for Hypertensive Disorders of Pregnancy
Reports vary in their cited frequency of preeclampsia and gestational hypertension, due in part to disparities in the many definitions used to classify the hypertensive disorders of pregnancy. In recent years, there has been increasing convergence in preeclampsia definitions, including those of the American College of Obstetrics and Gynecology (ACOG) Task Force on Hypertension in Pregnancy and the International Society for the Study of Hypertension in Pregnancy (ISSHP). Both bodies require new-onset systolic blood pressure ≥140 mm Hg or diastolic blood pressure of ≥90 mm Hg as the foundation for both gestational hypertension and preeclampsia. , Both definitions include proteinuria as part of the preeclampsia diagnosis but neither require proteinuria any longer. In recognition of the syndromic nature of preeclampsia, new onset of other maternal organ dysfunction may substitute for proteinuria and can be used to complete the diagnosis of preeclampsia. Types of maternal organ dysfunction included in the diagnostic criteria for preeclampsia are relatively consistent between ACOG and ISSHP: thrombocytopenia, renal insufficiency, impaired liver function, and headache (unresponsive to medication and unexplained by alternative diagnoses) or visual symptoms. The ACOG diagnostic criteria additionally include pulmonary edema, whereas the ISSHP criteria additionally include uteroplacental dysfunction (e.g., fetal growth restriction, abnormal umbilical artery [UA] Doppler wave form analysis, or stillbirth) in the presence of gestational hypertension but in the absence of proteinuria or other organ dysfunction. Further, the ISSHP criteria recognize additional hematological (disseminated intravascular coagulation and hemolysis) and neurological complications (altered mental state, stroke, and clonus) beyond thrombocytopenia and headache/visual symptoms recognized by ACOG. Both ACOG and ISHHP criteria for preeclampsia require confirmation of documentation of the elevated blood pressure and proteinuria on at least two occasions. However, neither ACOG nor ISHHP has mirrored the American Heart Association's hypertension guideline changes, which were adopted in 2013 and affirmed in 2017 to lower the diagnostic threshold for high blood pressure from ≥140 mm Hg SBP or ≥90 mm HG DBP to ≥130 mm Hg SBP or ≥80 DBP. For research purposes, both bodies have historically required documentation of normotension before 20 weeks' gestation and after 12 weeks’ postpartum; ISSHP previously recommended researchers to increase the specificity of preeclampsia diagnosis by requiring proteinuria. The most recent ACOG and ISSHP guidelines have not addressed definitions of preeclampsia specific to research settings. Other, less well-accepted definitions, often including clinical symptoms as diagnostic criteria, have also been used. Thus, the frequency of hypertensive disorders has been estimated based on different definitions that vary across geography and time. As expected, these changes in the diagnostic criteria by ACOG and ISSHP have led to a slight increase in the reported frequency of preeclampsia, although most studies examining this thus far have been small and/or single-center studies. , Importantly, application of this more inclusive definition identifies more women and babies at risk for adverse outcomes.
Most, but not all, studies of hypertension in pregnancy exclude women with preexisting hypertension; given this, few estimates of the prevalence of preeclampsia include superimposed preeclampsia. Superimposed preeclampsia is of increasing importance due to its strong association with adverse pregnancy outcomes , and its increase associated with rising obesity and chronic hypertension in young women.
Due to the potential for rapid and unanticipated worsening of preeclampsia, both ACOG and ISSHP now recommend against classifying cases of preeclampsia as either mild or severe in clinical practice. , However, both bodies support the recognition of “preeclampsia with severe features.” ACOG defines severe features as: (1) severe range high blood pressure (systolic blood pressure ≥160 mm Hg or diastolic blood pressure ≥110 mm Hg), (2) thrombocytopenia (platelet count <100 × 10 9 /L), (3) impaired liver function, unexplained by other diagnoses and indicated by abnormally elevated blood concentrations of liver enzymes (>2× the upper limit of normal) or by severe persistent right upper quadrant or epigastric pain, which is not responsive to medications, (4) renal insufficiency, (5) pulmonary edema, (6) new-onset headache (not explained by other diagnoses and unresponsive to medications), or (7) visual disturbances. The presence of any of these severe features is associated with an increased risk of maternal and fetal morbidity and mortality. Another factor associated with an increased risk of morbidity and mortality, as well as more severe placental and maternal/fetal clinical findings, is early-onset of preeclampsia before 34 weeks' gestation. , It should be noted that most large research studies use the gestational age at delivery, rather than the gestational age at diagnosis of preeclampsia, to distinguish “preterm” from “term” preeclampsia, as the latter is not usually available and is also subject to the frequency of prenatal visits.
In 2017, the American College of Cardiology and American Heart Association released updated guidelines for diagnosing high blood pressure among adults in the general population. For the first time, these guidelines lowered the diagnostic thresholds for diagnosing hypertension from 140 to 130 mm Hg systolic blood pressure and 90 to 80 mm Hg diastolic blood pressure and, in turn, expanded the number of individuals in the population classified as hypertensive. However, current guidelines for diagnosing hypertension during pregnancy have not yet adopted these lower thresholds for diagnosing high blood pressure among pregnant women. , Emerging and increasing evidence suggests that women meeting this contemporary, lower-threshold, general population definition of hypertension carry an increased risk for developing preeclampsia, as well as other adverse pregnancy outcomes, during pregnancy. What remains to be determined is whether this reclassification, which increases the number of women considered at risk, will result in advantages that outweigh the disadvantages of a larger “high risk” group.
Finally, changes in the international classification of hypertensive pregnancy have made it difficult to compare preeclampsia prevalence across time and place; for example, the ICD-10 system combines mild preeclampsia and gestational hypertension, while the ICD-9 system did not, resulting in a seeming drop in the prevalence of preeclampsia when statistics are compared across old and new versions. With these caveats in mind, we review below the literature on the prevalence of the hypertensive disorders of pregnancy. Illustrative studies, organized by case ascertainment method, are presented in Table 2.1 .
Table 2.1
Prevalence of Hypertensive Disorders of Pregnancy Since 1980 in Illustrative Studies, by Case Ascertainment Method
| S tudy | P opulation | Size (ICD) | P (HDP) | P (GH) | P (PE) | P (ECL) |
|---|---|---|---|---|---|---|
| Hypertensive disorders ascertained by general population registry or administrative database | ||||||
| Wallis, 2008 | US National Hospital Discharge Survey, 1987–2004 | ∼200,000 births per year (ICD-9) | 2.1% 3.0% (2004) |
2.7% 3.2% (2004) |
0.09% | |
| Fingar, 2017 | US Healthcare Cost and Utilization Project (HCUP) National (Nationwide) Inpatient Sample (NIS), 2014 | 3,796,490 delivery hospitalizations (ICD-9) | 10.8% | 3.8% | 4.6% | 0.07% |
| Goldenberg, 2011 | Iceland, US, UK, Singapore since 1980 | 0.02%–0.1% | ||||
| Roberts, 2011 (8 datasets, ∼1997–2007) | Alberta, Canada | 256,137 (ICD-10) | 6.0% | 1.4% | ||
| New South Wales, Australia | 732,288 (ICD-10) | 8.8% | 3.3% | |||
| Western Australia | 149,624 (ICD-10) | 9.1% | 2.9% | |||
| Denmark | 645,993 (ICD-10) | 3.6% | 2.7% | |||
| Norway | 456,353 (ICD-10) | 5.8% | 4.0% | |||
| Scotland | 531,622 (ICD-10) | 5.9% | 2.2% | |||
| Sweden | 913,779 (ICD-10) | 3.9% | 2.9% | |||
| Massachusetts, USA | 762,723 (ICD-9) | 7.0% | 3.3% | |||
| Gaio, 2001 | Brazilian Multicenter Cohort: 5 state capitals | 4892 hospital discharge records | 7.5% | 0.7% | 2.3% | 0.16% |
| Roberts CL, 2005 | New South Wales, 2000–02 | 250,173 | 9.8% | 4.3% | 4.2% | 0.06% |
| Hypertensive disorders ascertained by medical record review or study protocol (in placebo or standard care arms, where relevant) | ||||||
| Douglas, 1994 | UK, 1992. Case review. | All UK births | 0.05% | |||
| Knight, 2007 | UK, Feb 2005–Feb 2006. Case review. | All UK births | 0.03% | |||
| Souza, 2013 | WHO hospital survey in 29 countries in Asia, Africa, and Latin America | 314,623 | 2.5% | 0.3% | ||
| Conde-Agudelo, 2000 | Perinatal information System, Latin America and Caribbean (ICD-10) | 878,680 | 4.8% | 0.2% | ||
| Sibai, 1993 | Aspirin trial: US, healthy nulliparas | 1565 | 5.9% | 6.3% | ||
| Villar, 2001 | WHO Antenatal Care trial: Argentina, Cuba, Saudi Arabia, Thailand | 11,121 | 5.0% | 1.3% | 0.08% | |
| Lumbiganon, 2007 | 22 hospitals, Mexico City | 18,288 | 5.5% | 0.6% | ||
| 18 hospitals, Thailand | 17,525 | 1.9% | 0.3% | |||
| Chalumeau, 2002 | 6 West African countries, 1994–96 | 20,326 | 8.0% | 0.02% | ||
| Rotchell, 1998 | Barbados Aspirin Study: Maternity Hospital | 1822 | 7.3% | 4.6% | ||
| Roberts, 2010 | Antioxidant trial: US, healthy nulliparas | 4993 | 19.9% | 6.7% | 0.1% | |
| Vousden, 2019 | Pragmatic, stepped-wedge cluster randomized controlled trial (CRADLE intervention): 10 sites across Zimbabwe, Zambia, Sierra Leone, Malawi, Ethiopia Uganda, Haiti, and India; Apr 2016–Nov 2017 | 536,233 | 0.5% | |||
| Hypertensive disorders defined by mixed methods | ||||||
| Abalos, 2013 | Africa (AFRO) | 93,613 (57% Nigerian) | 4.0% | 2.7% | ||
| Americas (AMRO) | 36,693,594 (99% U.S.) | 2.3% | 1.1% | |||
| Eastern Mediterranean (EMRO) | 148,909 | 1.2% | 0.5% | |||
| European (EURO) | 1,093,782 | 3.8% | 0.1% | |||
| Southeast Asian (SEARO) | 203,159 | 2.7% | 1.3% | |||
| Western Pacific (WPRO) | 361,402 (69% Australian) | 4.2% | 0.1% | |||
Eclampsia
The most reliable estimate of the prevalence of eclampsia is likely that reported from a national survey in the United Kingdom. All obstetricians and all hospitals with an obstetrics unit were asked to participate in an active surveillance program in 1992. Each presumptive case was reviewed by a single obstetrician and was defined as eclamptic if there were seizures in the setting of hypertension, proteinuria, and either thrombocytopenia or an increased plasma aspartate transaminase concentration. The prevalence of eclampsia was estimated at 0.049% pregnancies. Most seizures occurred despite prenatal care (70%) and even after admission to the hospital (77%).
Table 2.1 shows a broad range of estimates of eclampsia incidence, ranging from 0.02% to 0.1% when ascertained in birth and other statistical registries and from 0.02% to 0.6% in studies with medical record review. The prevalence of eclampsia has declined rapidly during the 20th century in high-resource countries, from prevalences of 0.3% or more before 1930 to prevalences of 0.03% or less from the second half of the 20th century to present day. Chesley showed a marked reduction at Margaret Hague Maternity Hospital in Jersey City from 1931 to 1951 ( Table 2.2 ). In the United States, the risk of eclampsia dropped from an average annual rate of 0.10% in 1987–95 to 0.08% of deliveries from 1996 to 2004, even as rates of preeclampsia rose. Similar trends of declining rates of eclampsia have been observed in other countries as well. In Canada, the incidence of eclampsia decreased by half from 0.12% of deliveries in 2003 to 0.06% in 2009. In the Netherlands, the incidence of eclampsia decreased from 0.06% of deliveries from 2004 to 2006 to 0.02% from 2013 to 2016. The most recent data in the United States demonstrated that eclampsia impacted 0.07% of deliveries in 2014, based on nearly four million hospitalizations in the National (Nationwide) Inpatient Sample (NIS) ; this represents a 27% decrease from the rate of 0.09% observed in 2005.
Table 2.2
Incidence of Eclampsia in Clinic Patients at the Margaret Hague Maternity Hospital (Jersey City, United States)
| 1931–34 | 1935–39 | 1940–45 | 1946–51 | Totals | |
|---|---|---|---|---|---|
| Registrations | 12,604 | 17,407 | 12,022 | 12,208 | 54,241 |
| Cases of Eclampsia | 51 | 41 | 11 | 4 | 107 |
| % Incidence | 0.40 | 0.23 | 0.09 | 0.03 | 0.20 |
As pointed out several times by Leon Chesley, the reduction in eclampsia is largely related to improved medical care rather than a changing natural history of preeclampsia. This is supported by recent data from the Netherlands, which reported increased treatment with antihypertensive medication and magnesium sulfate during the same time intervals during which eclampsia incidence decreased. However, it is apparent that the major reduction in eclampsia occurred before the advent of these therapies in association with improvement, of perinatal observation of blood pressure and proteinuria and delivery of at-risk women, which likely represents an even more important improvement in care. The incidence of eclampsia and eclampsia-associated case fatality in low- and middle-resource countries remains high relative to high-resource countries. A 2013 systematic review estimated rates as high as 2.7% in Africa and as low as 0.1% in Europe . Incidence estimates of eclampsia also vary widely across low- and middle-resource countries. For example, the incidence of eclampsia ranged from 0.2% of deliveries in the capital of Zambia (Lusaka) to 1.4% in Sierra Leone between 2016 and 2017.
Preeclampsia
With the decline in eclampsia in high-resource countries, much of the recent epidemiologic research has focused on preeclampsia. Table 2.1 shows estimates of preeclampsia prevalence derived from registries, ranging from 1% to 4%, and from medical record review, ranging somewhat higher, at 1%–7%. In the United States, where reporting of preeclampsia is not mandatory, the prevalence of hypertensive pregnancies from 1979 through 2004 was estimated using a nationally representative sample of hospital discharge records. , Women with discharge diagnoses of gestational hypertension (ICD-9642.3), preeclampsia (ICD-9642.4 or 643.5), or eclampsia (ICD-9643.6) were included. The authors estimated that preeclampsia complicated 2.9% of pregnancies in 2003–04, a 25% increase since 1987. Similar prevalence of preeclampsia was estimated from hospital discharge data in the Danish National Birth Cohort of over 100,000 women recruited early in pregnancy, where the overall prevalence of preeclampsia was 3.0%, including 4.2% of nulliparous women and 1.3% of parous women. However, incidence of preeclampsia increased an additional 21% from 2005 to 2014 in the United States based on delivery hospitalization data from the NIS. This recent increase in the rate of preeclampsia among delivery hospitalizations was specifically driven by increases in the rate of severe preeclampsia, which increased by 50% from 11.6 per 1000 deliveries in 2005 to 17.4 per 1000 deliveries in 2014, and superimposed preeclampsia, which increased by 83% from 3.7 per 1000 deliveries in 2014 to 6.7 per 1000 deliveries in 2014. Women 35 years of age and older had a 36% increased rate of preeclampsia/eclampsia from 2005 to 2014 relative to women under age 20 who only experienced a 14% increase during the same time period. A higher percent change in the rate of preeclampsia/eclampsia was also reported for hospitals in the Northeast region of the United States (30%) and serving wealthier communities (28% among hospitals falling into the top quartile for community income).
A 2013 survey of multiple datasets published by Abalos (summarized in Table 2.1 ) revealed variability in regional preeclampsia rates, but did not suggest a pattern of especially high preeclampsia rates in lower-resource regions. Nevertheless, the maternal mortality attributed to the hypertensive disorders is considerably greater in lower-resource nations. The most recent WHO systematic analysis of global maternal mortality estimated that hypertensive disorders accounted for 13% of maternal mortality in developed regions, 16%–17% in Africa, 10%–15% in Asia, and 22% in Latin America and the Caribbean. Second only to hemorrhage, hypertensive disorders in pregnancy were one of the most common direct causes of maternal mortality worldwide.
Observational studies and randomized clinical trials that follow women prospectively with the express intent of documenting hypertensive disorders of pregnancy with standardized protocols often report modestly higher prevalences of these disorders than are captured retrospectively by hospital discharge or birth registry databases. In a more select population in the United States, the incidence of preeclampsia was estimated among control women enrolled in the NICHD Maternal Fetal Medicine Network for Clinical Trials (MFMU Network) trial of low-dose aspirin to prevent preeclampsia terminating in 1993. Included in the study were nulliparous women presenting to a series of academic medical centers for prenatal care. Women with a history of chronic hypertension, diabetes mellitus, renal disease, and other medical illnesses as well as women with a baseline blood pressure above 135/85 mm Hg were excluded. Among the 1500 women in the placebo group who were followed throughout pregnancy, 94 (6.3%) developed preeclampsia as defined by hypertension (systolic blood pressure of ≥140 mm Hg or a diastolic blood pressure of ≥90 mm Hg) plus proteinuria (either ≥300 mg/24 h or 2+ or more by dipstick on two or more occasions 4 h apart). In a 2010 study of more than 4500 control pregnancies using the same patient inclusion and exclusion and diagnostic criteria, the preeclampsia rate was remarkably similar, 6.7%. Other randomized clinical trials in the United States and Europe have demonstrated similar incidence rates for preeclampsia.
Superimposed preeclampsia, the development or worsening features of preeclampsia among women with chronic hypertension, has traditionally been excluded from research studies of hypertensive pregnancies. Estimates of the prevalence of superimposed preeclampsia are hard to come by, although many commentators have observed that it may be increasing as the prevalence of overweight and chronic hypertension rises among women of reproductive age. Among women with preexisting hypertension, preeclampsia develops in 10%–25%, as compared to a general population rate of 3%–7%. , In 2014, 29% of women with preexisting/chronic hypertension developed preeclampsia/eclampsia during pregnancy, based on data from the NIS. Superimposed preeclampsia occurred in 0.7% of delivery hospitalizations in the United States in 2014. Additionally, the more severe and longstanding the hypertension prior to pregnancy, the greater the risk of developing preeclampsia during pregnancy. In data from the MFMU Network, women with hypertension for at least 4 years' duration had a remarkably high rate of preeclampsia at 31%.
Gestational hypertension has been especially difficult to characterize, as it is notoriously underreported in registry databases. Estimated prevalences range from 1% to 4% from registries, but are considerably higher in studies that review medical records, on the order of 5%–7% ( Table 2.1 ). Wallis' analysis of the US National Hospital Discharge survey estimated that gestational hypertension complicated 3.0% of pregnancies in 2003–04, a prevalence that had increased by 184% since 1987. In 2014, gestational hypertension was reported in 3.8% of deliveries among US hospitalizations. Estimates derived from trials tend to be higher than those from observational studies or databases. The MFMU Network aspirin trial in 1993 estimated that 5.9% of control women developed gestational hypertension (hypertension as defined above without proteinuria) but was much higher, 19.9%, in a 2010 MFMU Network study and in another 1993 NICHD trial of healthy US nulliparous women (17.3%). Rates in most other studies are in agreement with the aspirin trial. ,
Discussion of Differential Frequency Estimates
Hospital-based incidence estimates for preeclampsia systematically differ from national estimates. Five main reasons are likely to account for this discrepancy. First, many studies, such as that by Saftlas and colleagues, rely on discharge diagnoses. Ales and Charlson performed a validation study of medical records at the New York Hospital and found that 25% of ICD-9 codes incorrectly diagnosed preeclampsia and that 53% of true cases were missed by ICD-9 coding. Similarly, Eskenazi and colleagues found that 47% of 263 women who received a discharge diagnosis of severe preeclampsia or eclampsia did not meet a rigorous set of criteria. Klemmenson and colleagues reported 2.9% prevalence of preeclampsia recorded in the Danish National Patient Registry, compared with 2.7% by medical record review and 3.4% by maternal recall. However, 26% of cases in the registry proved not to have preeclampsia by record review, and 31% of preeclampsia cases identified by record review were not recorded as such by the registry. The registry severely underestimated gestational hypertension compared with medical record review. Such underreporting of milder forms of pregnancy hypertension is widely reported. , Second, the MFMU Network studies included only nulliparous women, a group known to be at fivefold or greater risk of developing preeclampsia as compared to parous women. , Third, women electing to enroll in a randomized clinical trial to prevent preeclampsia may also be a group with characteristics predisposing to a tendency toward developing hypertension in pregnancy. However, the strict definition of preeclampsia used in the MFMU Network trials should have resulted in a decreased incidence estimate. Fourth, women seeking prenatal care at academic medical centers are a select group who may be at higher risk of developing pregnancy complications than would be reflected in a national sample. Fifth, data from the British Commonwealth in years past considered de novo hypertension without proteinuria as mild preeclampsia, and in these studies the diagnosis is substantially contaminated with women with transient hypertension. Nonetheless, a reasonable estimated range for the rate of preeclampsia in high-resource countries is 3%–7%.
It is worth noting that research studies in the United States commonly rely on maternal self-report to ascertain history of preeclampsia, given the absence of a nationwide registry. Reliance on maternal self-report is also typically the only data source available for large cohort studies, wherein the sample size may make medical record validation time-intensive and cost prohibitive, and for historical cohorts or longitudinal studies with long lengths of follow-up, for which participants' medical records may no longer be available. While a number validation studies of maternal self-report of hypertensive disorders in pregnancy have been conducted in recent decades, they are typically focused on preeclampsia and also vary in a number of important ways, including the comparator (or “gold standard”) used to validate self-report against, sample size, time since the preeclamptic pregnancy, and patient selection or demographic characteristics. , A 2015 systematic review of validation studies on maternal recall of hypertensive disorders in pregnancy found that sensitivity (the proportion of individuals correctly self-reporting a history of a hypertensive disorder among those who truly had the disorder according to the “gold standard” [e.g., medical record review]) was higher for preeclampsia than for gestational hypertension. The increased accuracy of preeclampsia recall, relative to gestational hypertension, may be due to the increased severity of the condition, which likely increases a woman's ability to remember and accurately report such a history. Cohort-based validation studies indicate that 73%–87% of women with medical record confirmed preeclampsia are able to correctly recall their preeclamptic pregnancy. , Sensitivity estimates are generally lower and less consistent for maternal recall of gestational hypertension, ranging from 31% to 100% in the 2015 systematic review. In addition to severity of the hypertensive disorder, the accuracy of maternal recall also appears to be impacted by maternal education level and parity. Length of recall may also impact accuracy due to memory impairment with time and changes in diagnostic criteria. Maternal self-report is also only as good as the quality of the information communicated to the woman at the time of diagnosis. Given the complexity of diagnostic criteria for hypertensive disorders of pregnancy, medical records, which are commonly used as the “gold standard” against which the accuracy of maternal recall is assessed, may be incomplete and unable to validate maternal recall even if the condition was diagnosed as reported. For example, a recent medical record validation of maternal self-report of preeclampsia in the Nurses' Health Study II found that 136 of 598 medical records had insufficient information to either confirm or reject a diagnosis of preeclampsia. Including records with insufficient information in the validation artificially lowered the positive predictive value to 69%, while excluding these records resulted in a PPV of 89%. Despite the limitations inherent in maternal recall, the fact that maternal recall of hypertensive disorders in pregnancy is predictive of clinical outcomes, including cardiovascular disease risk factors and events, , supports its utility in both research and practice.
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