- Email: [email protected]
Sleep effects on ambulatory blood pressure measurements in pregnant women
AJH
2001; 14:38 – 43
Sleep Effects on Ambulatory Blood Pressure Measurements in Pregnant Women Rennae S. Taylor, Greg Gamble, Lesley McCowan, and Robyn A. North The aim of this study was to investigate the effect of the definition of daytime and nighttime on ambulatory blood pressure (ABP) in pregnancy. To determine the prevalence of a ⬍10% decrease in mean arterial pressure with sleep (nondipper) in pregnancy and the consistency of nondipper status throughout pregnancy. In a prospective, longitudinal study, 102 pregnant woman underwent 24-h ABP monitoring and recorded sleep patterns at ⱕ14, 19 to 22, 27 to 30, 35 to 37 weeks’ gestation and 5 to 9 weeks’ postpartum. Nighttime was defined by arbitrary hours or actual periods of sleep. Ambulatory blood pressure measurements using the different definitions of nighttime were compared in the total cohort and individual women. Nondipper status of each woman was determined throughout pregnancy and postpartum. At 35 to 37 weeks’ gestation, 19% of women napped during the day and 20% were awake during the night. Throughout pregnancy, mean day and night systolic and diastolic ABP measurements were similar whether daytime and nighttime were defined by
A
arbitrary hours or by sleep periods. In individuals, the use of arbitrary hours (day 07:00 to 21:59, night 22:00 to 06:59) compared to sleep periods to define day and night resulted in differences in daytime systolic (SBP) and diastolic blood pressure (DBP) of up to 4 and 5 mm Hg, respectively. Similarly there were individual differences in nighttime SBP up to 10 mm Hg and DBP up to 11 mm Hg. A third of women were nondippers at least once during pregnancy, but only two women were consistent nondippers. The different definitions of day and night did not change group ABP measurements, but resulted in significant variation in ABP measurements in individual pregnant women. Nondippers were common and nondipper status frequently changed during pregnancy. Am J Hypertens 2001;14:38 – 43 © 2001 American Journal of Hypertension, Ltd. Key Words: Ambulatory blood pressure, pregnancy, sleep, dipper, nondipper.
mbulatory blood pressure (ABP) monitoring allows evaluation of the effect of daily activities on blood pressure (BP) throughout the 24-h period. In both nonpregnant and pregnant populations, nocturnal BP is lower than BP recorded during the daytime.1–3. In 1990, it was recommended that arbitrary hours be used to define nighttime.4 It is now recognized that use of arbitrary nighttime hours, while simplifying both collection and analysis of data, is not the optimal method to define sleep.5– 8 Blood pressure decreases with sleep and if the “nighttime” period does not accurately correlate with sleep, this will alter the nighttime BP reported. Pregnant women often have disturbed sleep patterns, with both nocturnal waking and daytime napping.9,10 Consequently, in pregnant women, the use of arbitrary hours to define daytime and nighttime may have even greater effects on the 24-h BP profile than in nonpregnant individuals. The majority of ABP studies in pregnant women have used arbitrary hours to define day and night. They have either split the 24-h period into two,11–13 or used
restricted day and night hours in an attempt to more closely reflect periods when women were actually awake or asleep.1,14 Other researchers have defined nighttime as periods of sleep recorded by individual pregnant women.3,15,16 There are no data in pregnant women comparing the effect on the 24-h BP profile of arbitrary hours to define nighttime versus individually documented sleep periods. The decrease in BP at night has been termed dipping and individuals who fail to have a significant nocturnal decrease in BP have been called nondippers.17 The method of defining daytime and nighttime influences the prevalence of nondippers in nonpregnant populations,6 but this has not been investigated in pregnant women. It is unknown how often healthy pregnant women are nondippers and whether a pregnant woman’s dipping status remains constant throughout pregnancy. This is of clinical relevance as it is recognized women with preeclampsia may have a minimal decrease in BP at nighttime or even an increase in nocturnal BP.13,18 Furthermore, it has been
Received January 3, 2000. Accepted May 30, 2000. From the Departments of Obstetrics and Gynaecology (RST, LM, RAN) and Medicine, University of Auckland, Auckland, New Zealand.
Address correspondence and reprint requests to R. A. North, Department of Obstetrics and Gynaecology, National Women’s Hospital, Claude Rd, Auckland 1003, New Zealand; e-mail: [email protected]
0895-7061/01/$20.00 PII S0895-7061(00)01226-7
© 2001 by the American Journal of Hypertension, Ltd. Published by Elsevier Science Inc.
AJH–January 2001–VOL. 14, NO. 1
SLEEP AND BLOOD PRESSURE DURING PREGNANCY
39
Table 1. Sleep patterns of pregnant and postpartum women during the 24-h clock
Time 12:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00
AM AM AM AM AM AM AM AM AM AM AM AM PM PM PM PM PM PM PM PM PM PM PM PM
Pregnancy Percent Asleep (n ⴝ 369)
Postpartum Percent Asleep (n ⴝ 86)
96 98 98 97 98 97 84 40 18 5 2 1 2 5 6 5 4 2 1 1 1 17 61 89
82 80 81 80 87 86 70 49 22 11 4 1 2 4 5 7 8 6 0 1 4 14 45 76
suggested women destined to develop preeclampsia may have a reduced nocturnal decrease in BP early in pregnancy.1,14 Other investigators have not confirmed this finding and the clinical significance of nondipping in pregnant women remains controversial.15 In a longitudinal study of healthy pregnant women our aims were 1) to compare ABP measurements when nighttime is defined by actual sleep periods with ABP measurements using arbitrary hours to define day and night; 2) to determine the prevalence of nondippers throughout pregnancy and the effect of the definition of nighttime on the frequency of nondippers; and 3) to determine the consistency of nondipper status during pregnancy.
Methods The study population comprised 102 healthy, normotensive women who were booked before 14 weeks’ gestation at a tertiary maternity hospital. Women underwent 24-h BP monitoring using the SpaceLabs 90207 ABP monitor (SpaceLabs Inc., Redmond, WA) at ⱕ14 weeks’, 19 to 22 weeks’, 27 to 30 weeks’, 35 to 37 weeks’ gestation, and 5 to 9 weeks postpartum. Women with essential hypertension, renal disease, diabetes, and multiple pregnancy were excluded. The regional health authority’s ethics committee approved the study and written informed consent was obtained from all participants. Gestational hypertension was defined as diastolic blood pressure (DBP) ⱖ90 mm
FIG. 1. Summary of ambulatory blood pressure (ABP) monitorings during pregnancy and postpartum.
Hg or systolic blood pressure (SBP) ⱖ140 mm Hg on more than two occasions after 20 weeks. Preeclampsia was defined as gestational hypertension plus proteinuria ⬎0.3g/day or ⱖ1 g/L on dipstick or multisystem disease. At each 24-h monitoring, the SpaceLabs 90207 ABP monitor was fitted to the nondominant arm, using an appropriate-sized cuff. During pregnancy, the recordings were made at 30-min intervals for 24 h. Postpartum BP was measured at 30-min intervals during the day and every 60 min for 8 h at night. The women were encouraged to follow their routine activities over the next 24 h. At the beginning of each ABP monitoring four mercury BP measurements were recorded. The women were given a diary and instructed to enter their activities in each 30-min interval. After the ABP monitoring, the diary was checked by the research midwife with the woman. Sleep and awake activities were then coded beside each BP measurement. All BP measurements and the activity data were transferred into SAS/Stat (SAS Institute Inc., Cary, NC) for analysis. Evaluations, which included assessment of interference with sleep, were completed by the women after the first, fourth, and postpartum ABP monitoring. The proportion of women asleep at each hour over the 24 h was calculated during pregnancy and postpartum (Table 1). Daytime and nighttime was defined by three different methods. 1.
2.
Diary method: nighttime was periods of actual sleep, as recorded in a woman’s diary. Nighttime by this definition included sleep periods during the day. Broad definition: daytime was 07:00 to 21:59 and night-
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SLEEP AND BLOOD PRESSURE DURING PREGNANCY
and nighttime, according to the method used to define daytime and nighttime, 2) there was a difference in ABP measurements in the daytime compared with the nighttime, and 3) there was an interaction between the three definitions and daytime/nighttime ABP measurements. Bland-Altman plots were constructed to show the variation in the differences between ABP measurements using the broad definition and ABP measurements according to the diary definition for individuals.19 The nocturnal decrease in BP was assessed by determining which women were nondippers. A nondipper was defined as an individual who had less than a 10% decrease in mean arterial pressure during sleep compared with awake mean arterial blood pressure.6,20 At each gestation period, we compared the proportion of women who were nondippers according to the three different methods to define day and night. Using actual sleep to define nighttime, we determined the consistency of nondipper status throughout pregnancy. Women were classified into four categories: consistent dipper, nondipper on one occasion, nondipper on two occasions, and nondipper always. The nondipper status of women who developed hypertensive complications is reported. 2 test was used to compare categoric groups. All tests were two-tailed and a 5% level of significance was maintained throughout.
Table 2. Proportion of women who napped during the day (09:00 to 18:00) or were awake at night (00:00 to 06:00) throughout pregnancy and postpartum
ⱕ14 weeks n ⫽ 102 19–22 weeks n ⫽ 95 27–30 weeks n ⫽ 91 35–37 weeks n ⫽ 81 Postpartum n ⫽ 86
Daytime Nappers
Awake at Night
21 (21%)
10 (10%)
10 (11%)
14 (15%)*
18 (20%)
12 (13%)
15 (19%)
16 (20%)*
20 (23%)
60 (71%)*
Values are given as n (%) * 19 –22 weeks n ⫽ 94, 35–37 weeks n ⫽ 80, postpartum n ⫽ 84 as nighttime recordings were incomplete.
3.
AJH–January 2001–VOL. 14, NO. 1
time 22:00 to 06:59. These time intervals were determined by the hours where the greatest proportion of women in our study made the transition from asleep to awake and from awake to asleep (Table 1). These hours are consistent with the 1990 recommendations.4 Tight definition: daytime was 09:00 to 20:59 and nighttime 00:00 to 05:59. These day and nighttime periods correlated with times when at least 94% of pregnant women in our study were awake or asleep, respectively.
Results One hundred two of the 120 women enrolled in the study completed the first ABP monitoring. The mean age of the women was 30.9 (SD 5) years, 84% were white, and 55% were nulliparous. Six women developed gestational hypertension and two developed preeclampsia. No woman was on antihypertensive medication during her antenatal ABP monitorings but one woman was on 320 mg/day of oxprenolol at the time of her postpartum monitoring. The num-
Ambulatory blood pressure values were grouped as follows and each group was analyzed separately: pregnant SBP, pregnant DBP, postpartum SBP, and postpartum DBP. The mixed models procedure (SAS), which efficiently allows for repeated measures, was used to determine whether: 1) ABP measurements differed for daytime
Table 3. Day and night ambulatory blood pressure measurements using three definitions of daytime and nighttime in pregnant and postpartum women 10–14 wk n ⴝ 102 Daytime Diary Awake Broad 07:00–21:59 Tight 09:00–20:59 Nighttime Diary Asleep Broad 22:00–06:59 Tight 00:00–05:59
19–22 wk n ⴝ 95
27–30 wk n ⴝ 91
35–37 wk n ⴝ 81
All Pregnancies n ⴝ 369
Postpartum n ⴝ 86
114 69 114 69 115 70
(7) (6) (8) (6) (7) (6)
113 68 113 68 114 69
(7) (6) (7) (6) (7) (6)
114 69 114 69 115 70
(7) (6) (7) (6) (7) (6)
118 73 118 73 119 74
(8) (6) (8) (6) (9) (6)
115 70 115 70 116 71
(8) (6) (8) (6) (8) (6)
115 73 114 72 115 73
(7) (6) (7) (6) (8) (6)
100 56 101 57 100 56
(7) (6) (7) (5) (7) (6)
98 54 99 55 98 54
(7) (5) (7) (5) (7) (5)
99 56 100 57 99 55
(7) (5) (7) (6) (7) (6)
106 60 107 61 106 60
(7) (6) (8) (6) (8) (6)
101 56 102 57 100 56
(8) (6) (8) (6) (8) (6)
102 60 104 62 103 61
(9) (7) (8) (6) (8) (6)
Blood pressure values are systolic and diastolic mean (SD) mm Hg.
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FIG. 2. Bland-Altman plots showing daytime difference for (A) systolic and (B) diastolic blood pressure against average of broad and diary daytime blood pressure. E represents those who were always awake; Πrepresents those who slept at some stage.
FIG. 3. Bland-Altman plots showing nighttime difference for (A) systolic and (B) diastolic blood pressure against average of broad and diary nighttime blood pressure. E represents those who were always asleep; Πrepresents those who were awake at some stage.
ber of women who underwent ABP monitoring at each gestation period and postpartum is shown in Fig. 1. In pregnancy, the median (interquartile range) of BP measurements during 24 h was 48 (47 to 49), with 31 (29 to 33) during the day and 17 (15 to 19) at night. This did not change throughout pregnancy. Postpartum BP was measured on 30 (28 to 32) occasions during the day, with 9 (7 to 10) measurements at night. Of the 21,336 BP measurements, sleep status according to diary entry was known on all but four occasions. Sleep patterns during the 24-h period are shown in Table 1. The proportion of women who napped at any stage during the day (09:00 to 18:00) or awoke at nighttime (00:00 to 05:59) is shown in Table 2. The percentage of women awake during the night increased from 10% in early pregnancy to 20% in the third trimester (P ⫽ .03). There was no change in perceived sleep disturbance because of the monitor from the first to the fourth ABP monitoring (P ⫽ .16) according to the evaluation forms.
Ambulatory blood pressure measurements according to the three methods of defining daytime and nighttime throughout pregnancy and postpartum are shown in Table 3. The upper limits of normal ABP range (mean, ⫹2 SD) for SBP and DBP in the daytime and nighttime, respectively, were 10 to 14 weeks 128/81 mm Hg and 114/68 mm Hg, 19 to 22 weeks 127/80 mm Hg and 112/64 mm Hg, 27 to 30 weeks 128/81 mm Hg and 113/66 mm Hg, 35 to 37 weeks 134/85 mm Hg and 122/72 mm Hg, and postpartum 129/85 mm Hg and 120/74 mm Hg. There was no difference in day or night SBP or DBP with the three definitions of daytime and nighttime. In all three definitions, SBP and DBP measurements were lower at nighttime than during the day (P ⬍ .0001). There was a different relationship between the definitions and daytime and nighttime ABP measurements for both SBP and DBP (P ⬍ .0001). Among the three definitions, the tight definition had the highest daytime BP values but the lowest nighttime ABP measurements.
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Consistency of nondipper status throughout pregnancy is summarized in Table 4. The two women who were consistent nondippers during pregnancy remained normotensive, delivered at term, and became dippers postpartum. One of the consistent nondippers had a father with essential hypertension and the other had a normotensive mother who had developed preeclampsia in her first pregnancy.
Discussion
FIG. 4. Proportion of nondippers at each gestation according to the method of defining daytime and nighttime. Diary definition ⫽ actual sleep and awake times. Tight definition ⫽ daytime (09:00 to 20:59) and nighttime (00:00 to 05:59). Broad definition ⫽ daytime (07:00 To 21:59) and nighttime (22:00 to 06:59). *P ⬍ .05 compared to diary definition at the same gestation.
Despite no difference in group means, in individuals there was variation in ABP measurements recorded with the broad definition and the actual sleep periods from the diaries (Figs. 2 and 3). In individuals, the difference between daytime ABP using the broad definition and using the diary definition were SBP ⫺4 to 4 mm Hg and DBP ⫺5 to 4 mm Hg. Similarly, the differences in individual women’s night ABP measurements using the broad and diary definitions were SBP ⫺3 to 10 mm Hg and DBP ⫺2 to 11 mm Hg. The mean (SD) decrease in SBP and DBP with sleep in pregnancy was 14 (6) and 13 (4), respectively. Fig. 4 shows a comparison of the proportion of nondippers according to the method of defining daytime and nighttime during pregnancy and postpartum. Using actual sleep periods to determine nighttime, the proportion of women who were nondippers at ⱕ14, 19 to 22, 27 to 30, and 35 to 37 weeks were 7.4%, 13.8%, 8.8%, and 20%, respectively (P ⫽ .05). Overall 32 (34%) of the 95 women were nondippers on at least one of their four ABP monitorings during pregnancy. There was no correlation between mercury office BP and nondipper status. Likewise, no correlation was found between nondipper status and whether a woman had daytime naps or was awake during the night.
Table 4.
Our study is the first report on the effect of the definition of daytime and nighttime on ABP measurements in pregnant women. This has potential importance because of altered sleep patterns in pregnancy. We found that 19% of women in the third trimester napped during the day and 20% were awake during the night. Defining nighttime by actual periods of sleep or by division of the 24-h clock into arbitrary hours did not alter the cohort’s mean daytime or nighttime ambulatory SBP or DBP. Despite these negligible group differences, the different methods to define day and night were associated with significant variation in the ABP measurements of individual women, as shown in the Bland Altman plots. For individuals, nighttime diastolic ABP differed up to 10 mm Hg systolic and 11 mm Hg when broad arbitrary hours were used to define nighttime compared with actual periods of sleep. During the daytime, systolic and diastolic ABP measurements using the broad and diary definitions differed by up to 4 and 5 mm Hg, respectively. These differences in ABP measurements with different definitions of day and night are of potential clinical significance when BP is mildly elevated. In this situation, the definition of daytime and nighttime on an ABP recording could alter whether or not a woman is classified as hypertensive. The definition of daytime and nighttime also altered the proportion of women classified as nondippers. Use of the broad day–night definition tended to classify more women as nondippers. As in nonpregnant populations,7 our data suggest actual periods of sleep should be used to define nighttime when analyzing the diurnal variation in pregnant women. One in three women were nondippers at some stage during pregnancy and dipping status was not consistent throughout pregnancy. A woman who was a nondipper on
Summary of nondipper status during pregnancy and association with pregnancy outcome Normotensive n ⴝ 87*
Consistent dipper Nondipper ⫻ 1 Nondipper ⫻ 2 Nondipper always
57 21 7 2
(66%) (24%) (8%) (2%)
Gestational Hypertension nⴝ6
Preeclampsia nⴝ2
5 1
1 1
Values are n (%). * Seven women had only a ⱕ14-week ABP monitoring (2 nondippers and 5 dippers) and were excluded.
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one occasion, was unlikely to be a nondipper on subsequent ABP monitoring during pregnancy. This has not been previously reported in pregnancy, but is in keeping with nonpregnant populations where there is little test– retest reliability in nondipper status.21,22 The proportion of nondippers increased in the third trimester to 20%, unrelated to the development of hypertension. Increased nocturnal wakening in the third trimester may contribute to this, as BP is lowest in stages III and IV of deep sleep23 and disturbed sleep patterns may reduce these periods of delta sleep. Consistent with this is the high rate (26%) of nondippers (night defined by sleep) in the postpartum period where 71% of women had broken sleep during the night. We found no relationship between dipping status and hypertensive complications in pregnancy. This is consistent with a previous study that found no difference in the nocturnal decrease in BP in women who later developed preeclampsia.15 However, our study did not have sufficient power to address this question. Our finding that nondipping is both a common and inconsistent occurrence during normal pregnancies, suggests it is unlikely nondipper status will be a useful predictor of preeclampsia. In conclusion, the method used to define day and night did not alter the cohort’s mean daytime and nighttime ABP. In the individual, clinically significant differences in daytime and nighttime ABP measurements may occur with the use of arbitrary hours to define nighttime rather than actual sleep periods. A third of women were nondippers on at least one occasion during pregnancy and nondipper status was not consistent throughout pregnancy.
Acknowledgments We thank Lesa Freeman for assistance with recruitment and monitoring of the women and Kevin Townend for computing assistance.
4.
5.
6.
7. 8.
9.
10. 11. 12.
13.
14.
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Halligan A, O’Brien E, O’Malley K, Mee F, Atkins N, Conroy R, Walshe JJ, Darling M: Twenty-four-hour ambulatory blood pressure measurement in a primigravid population. J Hypertens 1993;11: 869 – 873. Fogari R, Lusardi P, Zoppi A, Pasotti M, Corradi L: Effect of a westward transmeridian flight on ambulatory blood pressure monitoring in normotensive subjects. J Hypertens 1997;15:143–146. Brown MA, Robinson A, Bowyer L, Buddle ML, Martin A, Hargood JL, Cario GM: Ambulatory blood pressure monitoring in pregnancy: what is normal? Am J Obstet Gynecol 1998;178:836 – 842.
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The Scientific Committee: Consensus document on non-invasive ambulatory blood pressure monitoring. J Hypertens 1990;8 (suppl 6):S135–S140. Bursztyn M, Mekler J, Wachtel N, Ben-Ishay D: Siesta and ambulatory blood pressure monitoring: comparability of the afternoon nap and night sleep. Am J Hypertens 1994;7:217–221. Gatzka CD, Schmieder RE: Improved classification of dippers by individualized analysis of ambulatory blood pressure profiles. Am J Hypertens 1995;8:666 – 671. Pickering T: How should the diurnal changes of blood pressure be expressed? Am J Hypertens 1995;8:681– 682. May O, Arildsen H, Damsgaard EM: The diurnal variation in blood pressure should be calculated from individually defined day and night times. Blood Pressure 1998;7:103–108. Mead-Bennett E: The relationship of primigravid sleep experience and select moods on the first postpartum day. J Obstet Gynecol Neonatal Nurs 1990;19:146 –152. Sugihara K, Kobayashi T: Sleep behaviour of pregnant women using sleep log. Psychiatry Clin Neurosci 1998;52:201–202. Ferguson JH, Neubauer BL, Shaar CJ: Ambulatory blood pressure monitoring during pregnancy. Am J Hypertens 1994;7:838 – 843. Engfeldt P, Nisell H, Danielsson B, Lunell N-O, Aberg K, Aberg H: 24-hour ambulatory blood pressure monitoring in pregnant women with chronic hypertension: can it predict superimposed preeclampsia? Hypertens Pregnancy 1996;15:113–125. Halligan A, Shennan A, Lambert PC, deSwiet M, Taylor DJ: Diurnal blood pressure difference in the assessment of preeclampsia. Obstet Gynecol 1996;87:205–208. Higgins JR, Walshe JJ, Halligan A, O’Brien E, Conroy R, Darling MR: Can 24-hour ambulatory blood pressure measurement predict the development of hypertension in primigravidae? Br J Obstet Gynecol 1997;104:356 –362. Kyle PM, Clark SJ, Buckley D, Kissane J, Coats AJS, de Swiet M, Redman CWG: Second trimester ambulatory blood pressure in nulliparous pregnancy: a useful screening test for pre-eclampsia? Br J Obstet Gynaecol 1993;100:914 –919. Churchill D, Beevers DG: Differences between office and 24-hour ambulatory blood pressure measurement during pregnancy. Obstet Gynaecol 1996;88:455– 461. O’Brien E, Sheridan J, O’Malley K: Dippers and non-dippers (letter). Lancet 1988;ii:397. Redman CWG, Beilin LJ, Bonnar J: Reversed diurnal blood pressure rhythm in hypertensive pregnancies. Clin Sci Mol Med 1976; 51:687s– 689s. Bland JM, Altman DG: Comparing methods of measurement: why plotting difference against standard method is misleading. Lancet 1995;346:1085–1087. Verdecchia P, Schillaci G, Porcellati C: Dippers versus non-dippers. J Hypertens 1991;9 (suppl 8):S42–S44. Dimsdale JE, Heeren MM: How reliable is nighttime blood pressure dipping? Am J Hypertens 1998;11:606 – 609. Mochizuki Y, Okutani M, Donfeng Y, Iwasaki H, Takusagawa M, Kohno I, Mochizuki S, Umetani K, Ishii H, Ijiri H, Komori S, Tamura K: Limited reproducibility of circadian variation in blood pressure dippers and nondippers. Am J Hypertens 1998;11:403– 409. Schwan A, Eriksson G: Effect on sleep— but not on blood pressure— of nocturnal non-invasive blood pressure monitoring. J Hypertens 1992;10:189 –194.
2001; 14:38 – 43
Sleep Effects on Ambulatory Blood Pressure Measurements in Pregnant Women Rennae S. Taylor, Greg Gamble, Lesley McCowan, and Robyn A. North The aim of this study was to investigate the effect of the definition of daytime and nighttime on ambulatory blood pressure (ABP) in pregnancy. To determine the prevalence of a ⬍10% decrease in mean arterial pressure with sleep (nondipper) in pregnancy and the consistency of nondipper status throughout pregnancy. In a prospective, longitudinal study, 102 pregnant woman underwent 24-h ABP monitoring and recorded sleep patterns at ⱕ14, 19 to 22, 27 to 30, 35 to 37 weeks’ gestation and 5 to 9 weeks’ postpartum. Nighttime was defined by arbitrary hours or actual periods of sleep. Ambulatory blood pressure measurements using the different definitions of nighttime were compared in the total cohort and individual women. Nondipper status of each woman was determined throughout pregnancy and postpartum. At 35 to 37 weeks’ gestation, 19% of women napped during the day and 20% were awake during the night. Throughout pregnancy, mean day and night systolic and diastolic ABP measurements were similar whether daytime and nighttime were defined by
A
arbitrary hours or by sleep periods. In individuals, the use of arbitrary hours (day 07:00 to 21:59, night 22:00 to 06:59) compared to sleep periods to define day and night resulted in differences in daytime systolic (SBP) and diastolic blood pressure (DBP) of up to 4 and 5 mm Hg, respectively. Similarly there were individual differences in nighttime SBP up to 10 mm Hg and DBP up to 11 mm Hg. A third of women were nondippers at least once during pregnancy, but only two women were consistent nondippers. The different definitions of day and night did not change group ABP measurements, but resulted in significant variation in ABP measurements in individual pregnant women. Nondippers were common and nondipper status frequently changed during pregnancy. Am J Hypertens 2001;14:38 – 43 © 2001 American Journal of Hypertension, Ltd. Key Words: Ambulatory blood pressure, pregnancy, sleep, dipper, nondipper.
mbulatory blood pressure (ABP) monitoring allows evaluation of the effect of daily activities on blood pressure (BP) throughout the 24-h period. In both nonpregnant and pregnant populations, nocturnal BP is lower than BP recorded during the daytime.1–3. In 1990, it was recommended that arbitrary hours be used to define nighttime.4 It is now recognized that use of arbitrary nighttime hours, while simplifying both collection and analysis of data, is not the optimal method to define sleep.5– 8 Blood pressure decreases with sleep and if the “nighttime” period does not accurately correlate with sleep, this will alter the nighttime BP reported. Pregnant women often have disturbed sleep patterns, with both nocturnal waking and daytime napping.9,10 Consequently, in pregnant women, the use of arbitrary hours to define daytime and nighttime may have even greater effects on the 24-h BP profile than in nonpregnant individuals. The majority of ABP studies in pregnant women have used arbitrary hours to define day and night. They have either split the 24-h period into two,11–13 or used
restricted day and night hours in an attempt to more closely reflect periods when women were actually awake or asleep.1,14 Other researchers have defined nighttime as periods of sleep recorded by individual pregnant women.3,15,16 There are no data in pregnant women comparing the effect on the 24-h BP profile of arbitrary hours to define nighttime versus individually documented sleep periods. The decrease in BP at night has been termed dipping and individuals who fail to have a significant nocturnal decrease in BP have been called nondippers.17 The method of defining daytime and nighttime influences the prevalence of nondippers in nonpregnant populations,6 but this has not been investigated in pregnant women. It is unknown how often healthy pregnant women are nondippers and whether a pregnant woman’s dipping status remains constant throughout pregnancy. This is of clinical relevance as it is recognized women with preeclampsia may have a minimal decrease in BP at nighttime or even an increase in nocturnal BP.13,18 Furthermore, it has been
Received January 3, 2000. Accepted May 30, 2000. From the Departments of Obstetrics and Gynaecology (RST, LM, RAN) and Medicine, University of Auckland, Auckland, New Zealand.
Address correspondence and reprint requests to R. A. North, Department of Obstetrics and Gynaecology, National Women’s Hospital, Claude Rd, Auckland 1003, New Zealand; e-mail: [email protected]
0895-7061/01/$20.00 PII S0895-7061(00)01226-7
© 2001 by the American Journal of Hypertension, Ltd. Published by Elsevier Science Inc.
AJH–January 2001–VOL. 14, NO. 1
SLEEP AND BLOOD PRESSURE DURING PREGNANCY
39
Table 1. Sleep patterns of pregnant and postpartum women during the 24-h clock
Time 12:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00
AM AM AM AM AM AM AM AM AM AM AM AM PM PM PM PM PM PM PM PM PM PM PM PM
Pregnancy Percent Asleep (n ⴝ 369)
Postpartum Percent Asleep (n ⴝ 86)
96 98 98 97 98 97 84 40 18 5 2 1 2 5 6 5 4 2 1 1 1 17 61 89
82 80 81 80 87 86 70 49 22 11 4 1 2 4 5 7 8 6 0 1 4 14 45 76
suggested women destined to develop preeclampsia may have a reduced nocturnal decrease in BP early in pregnancy.1,14 Other investigators have not confirmed this finding and the clinical significance of nondipping in pregnant women remains controversial.15 In a longitudinal study of healthy pregnant women our aims were 1) to compare ABP measurements when nighttime is defined by actual sleep periods with ABP measurements using arbitrary hours to define day and night; 2) to determine the prevalence of nondippers throughout pregnancy and the effect of the definition of nighttime on the frequency of nondippers; and 3) to determine the consistency of nondipper status during pregnancy.
Methods The study population comprised 102 healthy, normotensive women who were booked before 14 weeks’ gestation at a tertiary maternity hospital. Women underwent 24-h BP monitoring using the SpaceLabs 90207 ABP monitor (SpaceLabs Inc., Redmond, WA) at ⱕ14 weeks’, 19 to 22 weeks’, 27 to 30 weeks’, 35 to 37 weeks’ gestation, and 5 to 9 weeks postpartum. Women with essential hypertension, renal disease, diabetes, and multiple pregnancy were excluded. The regional health authority’s ethics committee approved the study and written informed consent was obtained from all participants. Gestational hypertension was defined as diastolic blood pressure (DBP) ⱖ90 mm
FIG. 1. Summary of ambulatory blood pressure (ABP) monitorings during pregnancy and postpartum.
Hg or systolic blood pressure (SBP) ⱖ140 mm Hg on more than two occasions after 20 weeks. Preeclampsia was defined as gestational hypertension plus proteinuria ⬎0.3g/day or ⱖ1 g/L on dipstick or multisystem disease. At each 24-h monitoring, the SpaceLabs 90207 ABP monitor was fitted to the nondominant arm, using an appropriate-sized cuff. During pregnancy, the recordings were made at 30-min intervals for 24 h. Postpartum BP was measured at 30-min intervals during the day and every 60 min for 8 h at night. The women were encouraged to follow their routine activities over the next 24 h. At the beginning of each ABP monitoring four mercury BP measurements were recorded. The women were given a diary and instructed to enter their activities in each 30-min interval. After the ABP monitoring, the diary was checked by the research midwife with the woman. Sleep and awake activities were then coded beside each BP measurement. All BP measurements and the activity data were transferred into SAS/Stat (SAS Institute Inc., Cary, NC) for analysis. Evaluations, which included assessment of interference with sleep, were completed by the women after the first, fourth, and postpartum ABP monitoring. The proportion of women asleep at each hour over the 24 h was calculated during pregnancy and postpartum (Table 1). Daytime and nighttime was defined by three different methods. 1.
2.
Diary method: nighttime was periods of actual sleep, as recorded in a woman’s diary. Nighttime by this definition included sleep periods during the day. Broad definition: daytime was 07:00 to 21:59 and night-
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and nighttime, according to the method used to define daytime and nighttime, 2) there was a difference in ABP measurements in the daytime compared with the nighttime, and 3) there was an interaction between the three definitions and daytime/nighttime ABP measurements. Bland-Altman plots were constructed to show the variation in the differences between ABP measurements using the broad definition and ABP measurements according to the diary definition for individuals.19 The nocturnal decrease in BP was assessed by determining which women were nondippers. A nondipper was defined as an individual who had less than a 10% decrease in mean arterial pressure during sleep compared with awake mean arterial blood pressure.6,20 At each gestation period, we compared the proportion of women who were nondippers according to the three different methods to define day and night. Using actual sleep to define nighttime, we determined the consistency of nondipper status throughout pregnancy. Women were classified into four categories: consistent dipper, nondipper on one occasion, nondipper on two occasions, and nondipper always. The nondipper status of women who developed hypertensive complications is reported. 2 test was used to compare categoric groups. All tests were two-tailed and a 5% level of significance was maintained throughout.
Table 2. Proportion of women who napped during the day (09:00 to 18:00) or were awake at night (00:00 to 06:00) throughout pregnancy and postpartum
ⱕ14 weeks n ⫽ 102 19–22 weeks n ⫽ 95 27–30 weeks n ⫽ 91 35–37 weeks n ⫽ 81 Postpartum n ⫽ 86
Daytime Nappers
Awake at Night
21 (21%)
10 (10%)
10 (11%)
14 (15%)*
18 (20%)
12 (13%)
15 (19%)
16 (20%)*
20 (23%)
60 (71%)*
Values are given as n (%) * 19 –22 weeks n ⫽ 94, 35–37 weeks n ⫽ 80, postpartum n ⫽ 84 as nighttime recordings were incomplete.
3.
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time 22:00 to 06:59. These time intervals were determined by the hours where the greatest proportion of women in our study made the transition from asleep to awake and from awake to asleep (Table 1). These hours are consistent with the 1990 recommendations.4 Tight definition: daytime was 09:00 to 20:59 and nighttime 00:00 to 05:59. These day and nighttime periods correlated with times when at least 94% of pregnant women in our study were awake or asleep, respectively.
Results One hundred two of the 120 women enrolled in the study completed the first ABP monitoring. The mean age of the women was 30.9 (SD 5) years, 84% were white, and 55% were nulliparous. Six women developed gestational hypertension and two developed preeclampsia. No woman was on antihypertensive medication during her antenatal ABP monitorings but one woman was on 320 mg/day of oxprenolol at the time of her postpartum monitoring. The num-
Ambulatory blood pressure values were grouped as follows and each group was analyzed separately: pregnant SBP, pregnant DBP, postpartum SBP, and postpartum DBP. The mixed models procedure (SAS), which efficiently allows for repeated measures, was used to determine whether: 1) ABP measurements differed for daytime
Table 3. Day and night ambulatory blood pressure measurements using three definitions of daytime and nighttime in pregnant and postpartum women 10–14 wk n ⴝ 102 Daytime Diary Awake Broad 07:00–21:59 Tight 09:00–20:59 Nighttime Diary Asleep Broad 22:00–06:59 Tight 00:00–05:59
19–22 wk n ⴝ 95
27–30 wk n ⴝ 91
35–37 wk n ⴝ 81
All Pregnancies n ⴝ 369
Postpartum n ⴝ 86
114 69 114 69 115 70
(7) (6) (8) (6) (7) (6)
113 68 113 68 114 69
(7) (6) (7) (6) (7) (6)
114 69 114 69 115 70
(7) (6) (7) (6) (7) (6)
118 73 118 73 119 74
(8) (6) (8) (6) (9) (6)
115 70 115 70 116 71
(8) (6) (8) (6) (8) (6)
115 73 114 72 115 73
(7) (6) (7) (6) (8) (6)
100 56 101 57 100 56
(7) (6) (7) (5) (7) (6)
98 54 99 55 98 54
(7) (5) (7) (5) (7) (5)
99 56 100 57 99 55
(7) (5) (7) (6) (7) (6)
106 60 107 61 106 60
(7) (6) (8) (6) (8) (6)
101 56 102 57 100 56
(8) (6) (8) (6) (8) (6)
102 60 104 62 103 61
(9) (7) (8) (6) (8) (6)
Blood pressure values are systolic and diastolic mean (SD) mm Hg.
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FIG. 2. Bland-Altman plots showing daytime difference for (A) systolic and (B) diastolic blood pressure against average of broad and diary daytime blood pressure. E represents those who were always awake; Πrepresents those who slept at some stage.
FIG. 3. Bland-Altman plots showing nighttime difference for (A) systolic and (B) diastolic blood pressure against average of broad and diary nighttime blood pressure. E represents those who were always asleep; Πrepresents those who were awake at some stage.
ber of women who underwent ABP monitoring at each gestation period and postpartum is shown in Fig. 1. In pregnancy, the median (interquartile range) of BP measurements during 24 h was 48 (47 to 49), with 31 (29 to 33) during the day and 17 (15 to 19) at night. This did not change throughout pregnancy. Postpartum BP was measured on 30 (28 to 32) occasions during the day, with 9 (7 to 10) measurements at night. Of the 21,336 BP measurements, sleep status according to diary entry was known on all but four occasions. Sleep patterns during the 24-h period are shown in Table 1. The proportion of women who napped at any stage during the day (09:00 to 18:00) or awoke at nighttime (00:00 to 05:59) is shown in Table 2. The percentage of women awake during the night increased from 10% in early pregnancy to 20% in the third trimester (P ⫽ .03). There was no change in perceived sleep disturbance because of the monitor from the first to the fourth ABP monitoring (P ⫽ .16) according to the evaluation forms.
Ambulatory blood pressure measurements according to the three methods of defining daytime and nighttime throughout pregnancy and postpartum are shown in Table 3. The upper limits of normal ABP range (mean, ⫹2 SD) for SBP and DBP in the daytime and nighttime, respectively, were 10 to 14 weeks 128/81 mm Hg and 114/68 mm Hg, 19 to 22 weeks 127/80 mm Hg and 112/64 mm Hg, 27 to 30 weeks 128/81 mm Hg and 113/66 mm Hg, 35 to 37 weeks 134/85 mm Hg and 122/72 mm Hg, and postpartum 129/85 mm Hg and 120/74 mm Hg. There was no difference in day or night SBP or DBP with the three definitions of daytime and nighttime. In all three definitions, SBP and DBP measurements were lower at nighttime than during the day (P ⬍ .0001). There was a different relationship between the definitions and daytime and nighttime ABP measurements for both SBP and DBP (P ⬍ .0001). Among the three definitions, the tight definition had the highest daytime BP values but the lowest nighttime ABP measurements.
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Consistency of nondipper status throughout pregnancy is summarized in Table 4. The two women who were consistent nondippers during pregnancy remained normotensive, delivered at term, and became dippers postpartum. One of the consistent nondippers had a father with essential hypertension and the other had a normotensive mother who had developed preeclampsia in her first pregnancy.
Discussion
FIG. 4. Proportion of nondippers at each gestation according to the method of defining daytime and nighttime. Diary definition ⫽ actual sleep and awake times. Tight definition ⫽ daytime (09:00 to 20:59) and nighttime (00:00 to 05:59). Broad definition ⫽ daytime (07:00 To 21:59) and nighttime (22:00 to 06:59). *P ⬍ .05 compared to diary definition at the same gestation.
Despite no difference in group means, in individuals there was variation in ABP measurements recorded with the broad definition and the actual sleep periods from the diaries (Figs. 2 and 3). In individuals, the difference between daytime ABP using the broad definition and using the diary definition were SBP ⫺4 to 4 mm Hg and DBP ⫺5 to 4 mm Hg. Similarly, the differences in individual women’s night ABP measurements using the broad and diary definitions were SBP ⫺3 to 10 mm Hg and DBP ⫺2 to 11 mm Hg. The mean (SD) decrease in SBP and DBP with sleep in pregnancy was 14 (6) and 13 (4), respectively. Fig. 4 shows a comparison of the proportion of nondippers according to the method of defining daytime and nighttime during pregnancy and postpartum. Using actual sleep periods to determine nighttime, the proportion of women who were nondippers at ⱕ14, 19 to 22, 27 to 30, and 35 to 37 weeks were 7.4%, 13.8%, 8.8%, and 20%, respectively (P ⫽ .05). Overall 32 (34%) of the 95 women were nondippers on at least one of their four ABP monitorings during pregnancy. There was no correlation between mercury office BP and nondipper status. Likewise, no correlation was found between nondipper status and whether a woman had daytime naps or was awake during the night.
Table 4.
Our study is the first report on the effect of the definition of daytime and nighttime on ABP measurements in pregnant women. This has potential importance because of altered sleep patterns in pregnancy. We found that 19% of women in the third trimester napped during the day and 20% were awake during the night. Defining nighttime by actual periods of sleep or by division of the 24-h clock into arbitrary hours did not alter the cohort’s mean daytime or nighttime ambulatory SBP or DBP. Despite these negligible group differences, the different methods to define day and night were associated with significant variation in the ABP measurements of individual women, as shown in the Bland Altman plots. For individuals, nighttime diastolic ABP differed up to 10 mm Hg systolic and 11 mm Hg when broad arbitrary hours were used to define nighttime compared with actual periods of sleep. During the daytime, systolic and diastolic ABP measurements using the broad and diary definitions differed by up to 4 and 5 mm Hg, respectively. These differences in ABP measurements with different definitions of day and night are of potential clinical significance when BP is mildly elevated. In this situation, the definition of daytime and nighttime on an ABP recording could alter whether or not a woman is classified as hypertensive. The definition of daytime and nighttime also altered the proportion of women classified as nondippers. Use of the broad day–night definition tended to classify more women as nondippers. As in nonpregnant populations,7 our data suggest actual periods of sleep should be used to define nighttime when analyzing the diurnal variation in pregnant women. One in three women were nondippers at some stage during pregnancy and dipping status was not consistent throughout pregnancy. A woman who was a nondipper on
Summary of nondipper status during pregnancy and association with pregnancy outcome Normotensive n ⴝ 87*
Consistent dipper Nondipper ⫻ 1 Nondipper ⫻ 2 Nondipper always
57 21 7 2
(66%) (24%) (8%) (2%)
Gestational Hypertension nⴝ6
Preeclampsia nⴝ2
5 1
1 1
Values are n (%). * Seven women had only a ⱕ14-week ABP monitoring (2 nondippers and 5 dippers) and were excluded.
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one occasion, was unlikely to be a nondipper on subsequent ABP monitoring during pregnancy. This has not been previously reported in pregnancy, but is in keeping with nonpregnant populations where there is little test– retest reliability in nondipper status.21,22 The proportion of nondippers increased in the third trimester to 20%, unrelated to the development of hypertension. Increased nocturnal wakening in the third trimester may contribute to this, as BP is lowest in stages III and IV of deep sleep23 and disturbed sleep patterns may reduce these periods of delta sleep. Consistent with this is the high rate (26%) of nondippers (night defined by sleep) in the postpartum period where 71% of women had broken sleep during the night. We found no relationship between dipping status and hypertensive complications in pregnancy. This is consistent with a previous study that found no difference in the nocturnal decrease in BP in women who later developed preeclampsia.15 However, our study did not have sufficient power to address this question. Our finding that nondipping is both a common and inconsistent occurrence during normal pregnancies, suggests it is unlikely nondipper status will be a useful predictor of preeclampsia. In conclusion, the method used to define day and night did not alter the cohort’s mean daytime and nighttime ABP. In the individual, clinically significant differences in daytime and nighttime ABP measurements may occur with the use of arbitrary hours to define nighttime rather than actual sleep periods. A third of women were nondippers on at least one occasion during pregnancy and nondipper status was not consistent throughout pregnancy.
Acknowledgments We thank Lesa Freeman for assistance with recruitment and monitoring of the women and Kevin Townend for computing assistance.
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7. 8.
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