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Self-reported medical history information is included in many studies. However, data on the validity of Web-based questionnaires assessing medical history are scarce. If proven to be valid, Web-based questionnaires may provide researchers with an efficient means to collect data on this parameter in large populations.
The aim of this study was to assess the validity of a Web-based questionnaire on chronic medical conditions, allergies, and blood pressure readings against obstetric records and data from general practitioners.
Self-reported questionnaire data were compared with obstetric records for 519 pregnant women participating in the Dutch PRegnancy and Infant DEvelopment (PRIDE) Study from July 2011 through November 2012. These women completed Web-based questionnaires around their first prenatal care visit and in gestational weeks 17 and 34. We calculated kappa statistics (κ) and the observed proportions of positive and negative agreement between the baseline questionnaire and obstetric records for chronic conditions and allergies. In case of inconsistencies between these 2 data sources, medical records from the woman’s general practitioner were consulted as the reference standard. For systolic and diastolic blood pressure, intraclass correlation coefficients (ICCs) were calculated for multiple data points.
Agreement between the baseline questionnaire and the obstetric record was substantial (κ=.61) for any chronic condition and moderate for any allergy (κ=.51). For specific conditions, we found high observed proportions of negative agreement (range 0.88-1.00) and on average moderate observed proportions of positive agreement with a wide range (range 0.19-0.90). Using the reference standard, the sensitivity of the Web-based questionnaire for chronic conditions and allergies was comparable to or even better than the sensitivity of the obstetric records, in particular for migraine (0.90 vs 0.40,
Web-based questionnaires can be used to validly collect data on many chronic disorders, allergies, and blood pressure readings among pregnant women.
Self-reported methods of data collection are often applied in large-scale medical or biomedical studies for efficiency reasons. In these studies, it may not be feasible to conduct clinical measurements on all participants. Therefore, paper-and-pencil questionnaires or telephone interviews were traditionally used to gather information on the study variables. Nowadays, these modes of data collection are increasingly being substituted by Web-based questionnaires. However, knowledge on the validity of data collected with Web-based questionnaires is limited [
Most validation studies on medical history collected through self-reported methods has focused on chronic conditions, in particular cardiovascular diseases [
To the best of our knowledge, only Landkroon et al [
The Dutch prenatal care system is unique in the Western world. In the Netherlands, midwives are qualified to provide full prenatal care to all women with uncomplicated pregnancies and deliveries. The first prenatal care visit, which may be scheduled without referral of a general practitioner, usually takes place in gestational weeks 8 to 10 and frequent contacts are scheduled throughout pregnancy. Women are referred to a secondary or tertiary midwife or gynecologist in case of risk factors or complications. In 2013, 85% of pregnant women started their prenatal care in a primary care setting [
We used data from the PRegnancy and Infant DEvelopment (PRIDE) Study, an ongoing, prospective cohort study that enrolls Dutch women early in pregnancy. The PRIDE Study started enrollment in July 2011 in the Nijmegen region and aims at including more than 150,000 pregnancies to study a broad range of research questions pertaining to maternal and child health. Details on the study design are described elsewhere [
Through the baseline questionnaire, data on medical history were collected. Women were asked gateway questions to assess chronic conditions (“Do you have a chronic or long-term illness that was diagnosed by a medical doctor” followed by some examples of chronic conditions) and allergies (“Do you have an allergy or eczema?”). These questions were followed by multiple-choice questions with blank options to specify the chronic condition or allergy among those who answered positively to the relevant gateway question. Chronic conditions reported in other parts of the baseline questionnaire (eg, as causes for subfertility or as indications for medication use) were included in the analysis as well. In each prenatal questionnaire, we asked for the date of the most recent prenatal care visit, whether blood pressure was measured during this visit, and if so, for the systolic and diastolic blood pressure readings in mm Hg. A screenshot of the relevant parts of the questionnaires is provided in
A pretested, standardized case report form (CRF) was used to abstract data from the obstetric records of women who gave consent for medical record review. For logistical reasons, obstetric records were only reviewed in participating study centers in the Nijmegen region (7 midwifery practices and 1 academic hospital). Using the CRF, 2 medically trained abstracters collected data from the obstetric records on medical history, including chronic conditions, allergies, and pregnancy history, the pregnancy itself, anthropometrical measures including blood pressure taken during pregnancy, and pregnancy outcome, not all of which were included in this validation study.
Preexisting medical conditions are self-reported by the pregnant woman during the first prenatal care visit and are usually only recorded in the obstetric record by the prenatal care provider if deemed important for the course of pregnancy or the delivery [
Chronic conditions were classified and coded according to the World Health Organization’s
Only PRIDE Study participants with complete information on chronic conditions, allergies, and blood pressure during the most recent prenatal care visit in the baseline questionnaire who gave consent to review their medical records were included in this validation study. For chronic conditions and allergies with at least 5 cases in either the questionnaire or the obstetrical record, we calculated kappa statistics (κ) to quantify agreement between the baseline questionnaire and the obstetric record regarding chronic conditions and allergies. We also calculated the observed proportions of positive and negative agreement (ppos and pneg, respectively) because kappa is strongly affected by imbalances in marginal totals (ie, a low kappa despite a high level of agreement) [
To determine which method of data collection was most valid to collect information on chronic conditions and allergies among pregnant women, sensitivity and specificity were calculated with GP data until the date of completion of the baseline questionnaire as our reference standard. When GP data were unavailable, pharmacy records were screened for diagnoses of chronic conditions or allergies and for medication dispensed that was indicative for chronic conditions or allergies. In addition to the discordant questionnaire–obstetric record pairs, women with positive scores on both the Web-based questionnaire and the obstetric record were included in these calculations as true positives. Likewise, women with negative scores on both methods were included as true negatives. We assessed potential differences in sensitivity and specificity between the questionnaires and the obstetric records using chi-square tests.
For the validity analyses regarding blood pressure readings, only women with an exact match between the date of the most recent prenatal care visit reported in any of the prenatal questionnaires and a visit date recorded in the obstetric record were included to be certain that both data sources referred to the same measurement. Intraclass correlation coefficients (ICCs) with 95% confidence intervals (CIs) for systolic blood pressure (SBP) and diastolic blood pressure (DBP) were calculated using 2-way mixed effects models (single measure). To assess absolute agreement and potential differences in bias within the SBP and DBP range, we plotted the difference in blood pressure readings between the questionnaire and the obstetric record (y-axis) against the mean of the 2 methods of data collection (x-axis) according to the Bland-Altman technique [
Calculation of positive and negative agreement between two tests.
Women enrolled in the PRIDE Study between July 2011 through November 2012 were eligible for this study (N=725). The overall participation rate in the PRIDE Study was 42.90% (725/1690) during this time period.
Flow chart of study participants.
Characteristics of PRIDE Study participants included in this validation study and participants who did not give consent for review of medical records.
Characteristic | Participants in validation study, n (%) |
No consent for medical record review, n (%) |
|
|
|
|
|
.45 | |
|
<25 | 15 (2.9) | 2 (1.1) |
|
|
25-29 | 172 (33.1) | 52 (29.9) |
|
|
30-34 | 238 (45.9) | 88 (50.6) |
|
|
≥35 | 94 (18.1) | 32 (18.4) |
|
|
|
|
.20 | |
|
Netherlands | 483 (93.1) | 154 (88.5) |
|
|
Other | 31 (6.0) | 15 (8.6) |
|
|
|
|
.03 | |
|
Low/intermediate | 107 (20.6) | 22 (12.6) |
|
|
High | 407 (78.4) | 147 (84.5) |
|
|
|
|
.62 | |
|
0 | 232 (44.7) | 74 (42.5) |
|
|
≥1 | 287 (55.3) | 100 (57.5) |
|
|
|
|
.06 | |
|
Underweight (<18.5 kg/m2) | 15 (2.9) | 2 (1.1) |
|
|
Normal (18.5-24.9 kg/m2) | 336 (64.7) | 122 (70.1) |
|
|
Overweight (25.0-29.9 kg/m2) | 90 (17.3) | 27 (15.5) |
|
|
Obese (≥30 kg/m2) | 33 (6.4) | 3 (1.7) |
|
|
Height/weight unknown | 45 (8.7) | 20 (11.5) |
|
|
|
|
.17 | |
|
<8 | 96 (18.5) | 41 (23.6) |
|
|
8-10 | 178 (34.3) | 48 (27.6) |
|
|
>10 | 245 (47.2) | 85 (48.9) |
|
|
|
|
.02 | |
|
Completed before first prenatal care visit | 131 (25.2) | 60 (34.5) |
|
|
Completed after first prenatal care visit | 388 (74.8) | 114 (65.5) |
|
a Numbers may not add up to total group size due to missing values.
b Difference between the 2 groups using chi-square tests.
c High level of education: completed higher vocational education or university.
d Body mass index (BMI) derived from self-reported height and weight.
Of the 519 participants, 118 (22.7%) women reported having a chronic condition in the baseline questionnaire, whereas chronic conditions were recorded in the obstetric records of 105 (20.2%) women. Overall, agreement between the Web-based questionnaire and the obstetric record was substantial for any chronic condition (κ=.61;
Agreement between data from the Web-based questionnaire and obstetric record for chronic conditions (n=519).
Chronic condition | Questionnaire positive, n | Questionnaire negative, n | κ | ppos a | pneg b | ||
|
Record positive | Record negative | Record positive | Record negative |
|
|
|
Any chronic condition | 77 | 41 | 28 | 373 | .61 | 0.69 | 0.92 |
Diseases of the blood and blood-forming organs | 2 | 0 | 0 | 517 | — | — | — |
Thalassemia | 1 | 0 | 0 | 518 | — | — | — |
Immunodeficiency | 1 | 0 | 0 | 518 | — | — | — |
Endocrine, nutritional, and metabolic diseases | 15 | 5 | 6 | 493 | .72 | 0.73 | 0.99 |
Thyroid disease | 9 | 1 | 1 | 508 | .90 | 0.90 | 1.00 |
Polycystic ovarian syndrome | 5 | 3 | 5 | 506 | .55 | 0.56 | 0.99 |
Hypercholesterolemia | 0 | 1 | 0 | 518 | — | — | — |
Periodic fever syndrome | 1 | 0 | 0 | 518 | — | — | — |
Mental and behavioral disorders | 7 | 6 | 4 | 502 | .57 | 0.58 | 0.99 |
Depression/anxiety | 5 | 5 | 4 | 505 | .52 | 0.53 | 0.99 |
Posttraumatic stress disorder | 1 | 1 | 0 | 517 | — | — | — |
ADD/ADHDc | 1 | 1 | 0 | 517 | — | — | — |
Diseases of the nervous system | 12 | 17 | 4 | 486 | .51 | 0.53 | 0.98 |
Multiple sclerosis | 1 | 0 | 0 | 518 | — | — | — |
Epilepsy | 4 | 0 | 1 | 514 | .89 | 0.89 | 1.00 |
Migraine | 4 | 17 | 1 | 497 | .30 | 0.31 | 0.98 |
Tension-type headache | 1 | 0 | 1 | 517 | — | — | — |
Chronic fatigue syndrome | 2 | 0 | 1 | 516 | — | — | — |
Diseases of the circulatory system | 1 | 1 | 5 | 512 | .25 | 0.25 | 0.99 |
Hypertension | 0 | 0 | 3 | 516 | — | — | — |
Cardiac arrhythmia | 0 | 1 | 1 | 517 | — | — | — |
Raynaud syndrome | 1 | 0 | 1 | 517 | — | — | — |
Diseases of the respiratory system | 19 | 17 | 5 | 478 | .61 | 0.63 | 0.98 |
Asthma | 19 | 17 | 5 | 478 | .61 | 0.63 | 0.98 |
Diseases of the digestive system | 8 | 4 | 6 | 501 | .61 | 0.62 | 0.99 |
Crohn disease | 2 | 0 | 1 | 516 | — | — | — |
Ulcerative colitis | 3 | 0 | 0 | 516 | — | — | — |
Irritable bowel syndrome | 3 | 4 | 5 | 507 | .39 | 0.40 | 0.99 |
Diseases of the skin and subcutaneous tissue | 4 | 7 | 1 | 507 | .49 | 0.50 | 0.99 |
Psoriasis | 4 | 5 | 0 | 510 | .61 | 0.62 | 1.00 |
Rosacea | 0 | 2 | 1 | 516 | — | — | — |
Diseases of the musculoskeletal system and connective tissue | 9 | 4 | 4 | 502 | .68 | 0.69 | 0.99 |
Rheumatoid arthritis | 2 | 2 | 0 | 515 | — | — | — |
Sjögren syndrome | 1 | 0 | 0 | 518 | — | — | — |
Ankylosing spondylitis | 1 | 0 | 1 | 517 | — | — | — |
Hypermobility | 1 | 1 | 3 | 514 | — | — | — |
Fibromyalgia | 2 | 2 | 1 | 514 | — | — | — |
Complex regional pain syndrome | 1 | 0 | 0 | 518 | — | — | — |
Diseases of the genitourinary tract | 4 | 1 | 2 | 512 | .72 | 0.73 | 1.00 |
Endometriosis | 1 | 1 | 1 | 516 | — | — | — |
Lichen sclerosis | 3 | 0 | 1 | 515 | — | — | — |
a Observed proportion of positive agreement.
b Observed proportion of negative agreement.
c ADD: attention deficit disorder; ADHD: attention deficit hyperactivity disorder.
Allergies were reported by 229 of 519 (44.1%) women in the baseline questionnaire and recorded in the obstetric record of 168 (32.4%) women. In
Agreement between data from a Web-based questionnaire and obstetric record for allergies (n=519).
Allergy | Questionnaire positive, n | Questionnaire negative, n | κ | ppos a | pneg b | ||
|
Record positive | Record negative | Record positive | Record negative |
|
|
|
Any allergy | 138 | 91 | 30 | 260 | .51 | 0.70 | 0.81 |
Inhalation allergies | 80 | 83 | 10 | 346 | .53 | 0.63 | 0.88 |
Hay fever | 53 | 53 | 3 | 410 | .60 | 0.65 | 0.94 |
Allergies to animals | 21 | 45 | 7 | 446 | .40 | 0.45 | 0.94 |
House dust mite allergy | 15 | 15 | 22 | 467 | .41 | 0.45 | 0.96 |
Food allergies | 15 | 39 | 1 | 464 | .40 | 0.43 | 0.96 |
Allergic contact dermatitis | 33 | 73 | 11 | 402 | .36 | 0.44 | 0.91 |
Allergies to metal | 11 | 37 | 3 | 468 | .33 | 0.35 | 0.96 |
Fragrance hypersensitivity | 6 | 51 | 0 | 462 | .17 | 0.19 | 0.95 |
Plaster allergy | 9 | 16 | 7 | 487 | .42 | 0.44 | 0.98 |
Latex allergy | 4 | 0 | 3 | 512 | .73 | 0.73 | 1.00 |
Insect sting allergy | 3 | 20 | 1 | 495 | .21 | 0.22 | 0.98 |
Drug allergies | 26 | 9 | 15 | 469 | .66 | 0.68 | 0.98 |
Other allergies | 2 | 3 | 0 | 514 | .57 | 0.57 | 1.00 |
a Observed proportion of positive agreement.
b Observed proportion of negative agreement.
Regarding the 254 women with an inconsistency between the Web-based questionnaire and the obstetric record for chronic conditions or allergies, complete GP data were obtained for 194 (76.4%) women; the GP was unknown for 12 women, 21 women were not registered with the GP whose name was provided, the GP did not respond to our multiple data requests for 25 women, and GP records were incomplete for 2 women. For 7 women lacking GP data, the diagnosis of a chronic disorder was ascertained from their pharmacy records. Generally, sensitivity was better for the Web-based questionnaire than for the obstetric record when compared to GP data (
Validity comparisons of chronic conditions and allergies among pregnant women: Web-based questionnaires and obstetric records compared to GP records.
Condition or allergy | n | Sensitivity | Specificity | ||||
|
|
Questionnaire | Record |
|
Questionnaire | Record |
|
Any chronic condition | 496 | 0.83 | 0.74 | .14 | 0.93 | 0.92 | .79 |
Endocrine, nutritional, and metabolic diseases | 515 | 0.76 | 0.70 | .73 | 1.00 | 0.99 | .41 |
Thyroid disease | 518 | 0.77 | 0.69 | .66 | 1.00 | 1.00 | >.99 |
Polycystic ovarian syndrome | 516 | 0.67 | 0.83 | .52 | 1.00 | 0.99 | .41 |
Mental and behavioral disorders | 516 | 0.45 | 0.27 | .39 | 0.99 | 0.99 | .78 |
Depression/anxiety | 516 | 0.50 | 0.30 | .37 | 0.99 | 0.99 | .48 |
Diseases of the nervous system | 513 | 0.85 | 0.65 | .15 | 0.99 | 1.00 | .09 |
Epilepsy | 519 | 0.80 | 1.00 | .32 | 1.00 | 1.00 | >.99 |
Migraine | 514 | 0.90 | 0.40 | .02 | 0.99 | 1.00 | .03 |
Diseases of the respiratory system | 511 | 0.86 | 0.61 | .04 | 0.99 | 0.99 | .76 |
Asthma | 511 | 0.86 | 0.61 | .04 | 0.99 | 0.99 | .76 |
Diseases of the digestive system | 517 | 0.58 | 0.67 | .68 | 0.99 | 0.99 | .74 |
Irritable bowel syndrome | 517 | 0.33 | 0.33 | >.99 | 0.99 | 0.99 | .74 |
Diseases of the skin and subcutaneous tissue | 519 | 0.69 | 0.38 | .12 | 1.00 | 1.00 | .16 |
Psoriasis | 519 | 0.80 | 0.40 | .08 | 1.00 | 1.00 | .32 |
Diseases of the musculoskeletal system and connective tissue | 515 | 1.00 | 0.82 | .15 | 1.00 | 1.00 | .16 |
Diseases of the genitourinary tract | 518 | 0.80 | 1.00 | .32 | 1.00 | 1.00 | .32 |
Any allergy | 494 | 0.96 | 0.85 | .007 | 0.74 | 0.85 | .009 |
Inhalation allergies | 496 | 0.92 | 0.74 | .003 | 0.83 | 0.93 | <.001 |
Hay fever | 508 | 0.90 | 0.64 | .001 | 0.91 | 0.96 | .001 |
Allergies to animals | 509 | 0.89 | 0.53 | .01 | 0.91 | 0.97 | <.001 |
House dust mite allergy | 512 | 0.58 | 0.65 | .58 | 0.98 | 0.97 | .44 |
Food allergies | 511 | 1.00 | 0.86 | .32 | 0.92 | 0.98 | <.001 |
Allergic contact dermatitis | 502 | 1.00 | 1.00 | >.99 | 0.84 | 0.94 | <.001 |
Allergies to metal | 508 | 1.00 | 1.00 | >.99 | 0.94 | 0.99 | <.001 |
Fragrance hypersensitivity | 507 | 1.00 | 1.00 | >.99 | 0.91 | 0.99 | <.001 |
Plaster allergy | 511 | 1.00 | 1.00 | >.99 | 0.96 | 0.97 | .36 |
Drug allergies | 515 | 0.84 | 0.95 | .30 | 0.97 | 0.96 | .32 |
a Difference between the 2 modes of data collection using chi-square tests.
For 4 chronic conditions, additional self-reports were identified in the questions about causes of subfertility that preceded the chronic condition question (polycystic ovarian syndrome [n=7] and endometriosis [n=2]) and through medication use (rosacea [n=2] and lichen sclerosis [n=1]). When these women were considered as not having reported these chronic conditions, agreement between the Web-based questionnaire and the obstetric record decreased, except for skin diseases. Furthermore, it decreased the sensitivity of the questionnaire, especially for endocrine diseases (0.67), polycystic ovarian syndrome (no true positive subjects), and diseases of the genitourinary tract (0.67).
Analyses on the validity of the Web-based questionnaires for blood pressure readings could not be conducted on the complete study sample. At baseline, 123 of 519 (23.7%) women did not have a prenatal care visit yet and, therefore, no valid blood pressure measurement (
Validity analyses comparing Web-based questionnaires and obstetric records for systolic and diastolic blood pressure readings: sample description and intraclass correlation coefficients.
Characteristic | Baseline questionnaire |
Questionnaire 2 |
Questionnaire 3 |
|
Did not have prenatal care visit yet, n | 123 | 0 | 0 | |
No match date prenatal care visit, n | 91 | 65 | 32 | |
Questionnaire: blood pressure not measured, n | 33 | 30 | 1 | |
Questionnaire: blood pressure unknown, n | 76 | 93 | 50 | |
Obstetric record: blood pressure not recorded, n | 11 | 12 | 1 | |
Included in validity analyses, n | 185 | 223 | 211 | |
|
|
|
|
|
|
Systolic | 0.72 (0.65-0.79) | 0.92 (0.89-0.94) | 0.90 (0.88-0.93) |
|
Diastolic | 0.79 (0.73-0.84) | 0.91 (0.88-0.93) | 0.89 (0.86-0.91) |
At baseline, the ICCs for SBP and DBP were 0.72 (95% CI 0.65-0.79) and 0.79 (95% CI 0.73-0.84), respectively. In the follow-up questionnaires, ICCs were substantially higher, ranging between 0.89 (95% CI 0.86-0.91; DBP in questionnaire 3) and 0.92 (95% CI 0.89-0.94; SBP in questionnaire 2). The Bland-Altman plots (
Bland-Altman plots showing the differences in reported systolic blood pressure (SBP) and diastolic blood pressure (DBP) between the 3 Web-based questionnaires and the obstetric record plotted against the mean of the 2 methods of data collection. Each data point shows one participant. The short dashed line shows the mean difference. The long dashed lines show the 95% limits of agreement (mean difference ±2 SD).
Web-based questionnaires are increasingly being used as a method of data collection in medical research. The results from the present study show that data on many chronic conditions and allergies can be validly collected among pregnant women using Web-based questionnaires with sensitivities comparable to or even higher than obstetric records. However, some overreporting of allergies was observed and absence of disease was more accurately reported than presence of disease. In addition, pregnant women were able to reliably recall blood pressure readings from the most recent prenatal care visit, especially in the follow-up questionnaires, but a substantial proportion of women could not remember their blood pressure readings at all.
In addition to the relatively large sample size, the use of GP records as a reference standard to validate the Web-based questionnaire and obstetric records for chronic conditions and allergies is a major strength of this study. In the Netherlands, inhabitants are obligatory listed with one GP, who coordinates access to specialized care and always receives all relevant medical information about the patient [
Women participating in the PRIDE Study represent a highly educated population, potentially limiting the generalizability of our results. However, women included in the validation study had a lower level of education compared to women who did not give consent for review of medical records. Previous studies on the association between maternal level of education and recall sensitivity of pregnancy-related events showed inconsistent results [
Validity could not be determined reliably for a number of specific chronic conditions due to their low prevalence rates in our study population or in strata based on baseline characteristics. However, it was not feasible to increase the size of the study population because medical record abstraction is a labor-intensive process. Moreover, during the time frame of this study, only one secondary/tertiary care facility participated in the PRIDE Study. Women with certain medical conditions, including preexisting hypertension or diabetes and rheumatoid arthritis, are often referred to these facilities for prenatal care in the Netherlands. Reassuringly, only a small proportion of pregnant women (15%) start prenatal care in a secondary or tertiary care setting, mainly because of complications in a previous pregnancy [
For many chronic conditions that were included in our analyses, data on the validity of self-report are scarce due to differences in study populations between this study among pregnant women and previous studies, which often selected an older population with higher prevalences of cardiovascular diseases, diabetes, and cancer. However, the general pattern of a better agreement for chronic conditions that have clear diagnostic criteria than for conditions that are less well-defined observed previously [
Surprisingly, sensitivity of the Web-based questionnaire was substantially higher for asthma (0.86) and migraine (0.90) compared to the obstetric record, whereas the specificities were comparable. The traditional self-reported modes of data collection have a sensitivity ranging between 0.55 and 0.95 (median 0.72) for asthma [
With regard to allergies, the Web-based questionnaire also seemed to be more sensitive than the obstetric record, but at the expense of its specificity indicating that overreporting occurs with the use of the Web-based questionnaire and underreporting is present when using obstetric records. However, participants with allergic symptoms who manage their symptoms with over-the-counter medication may not be registered as allergic in GP records, resulting in a lower specificity (increased number of false positives). Therefore, skin-prick tests or serum-specific immunoglobulin E levels may be a more appropriate reference standard. In comparison with previous studies in different populations [
Research interests in changes in blood pressure over time in relation to disease outcomes is growing (eg, [
We showed that Web-based questionnaires can validly collect data on many chronic disorders, including asthma, migraine, and thyroid disease, and also allergies among pregnant women with equal or better data quality compared to obstetric records. Although a substantial proportion of women could not remember their blood pressure readings, pregnant women who did recall the readings, recalled them well. This indicates that accurate data on general health characteristics may be collected using Web-based questionnaires in this population.
Screenshots of the Web-based questionnaire.
body mass index
case report form
diastolic blood pressure
general practitioner
intraclass correlation coefficient
observed proportion of negative agreement
observed proportion of positive agreement
PRegnancy and Infant DEvelopment
systolic blood pressure
termination of pregnancy
This work was supported by a grant from the Lung Foundation Netherlands and grants to the PRIDE Study from the Netherlands Organisation for Health Research and Development (ZonMw).
None declared.