Abstract
Introduction
A recent study at the Maroua Provincial Hospital revealed that hypertension in pregnancy was the first cause of maternal death, representing 17.5% of the 63 maternal deaths recorded between 2003 and 2005. Knowing little about the causes, this study was to identify the possible risk factors for hypertensive disorders in pregnancy.
Methods
This case-control study was-done at the Maroua Regional Hospital, Cameroon between June 2005 and May 2007. All the 152 deliveries complicated with hypertension were compared and analyzed with 414 pregnancies that were not complicated with the disease. Data analysis was performed using EPI Info 3.5.1. The differences were considered to be significant if the p-values were less than 0.05.
Results
Using univariate analysis, several factors linked to hypertensive disorder in pregnancy were identified. They included early adolescence, nulliparity, illiteracy, lack of occupation and family history of hypertension. At multivariate analysis, the risk of having hypertension during pregnancy remained greater for illiterate women (OR: 1.6; 95%CI: 1.0-2.3), housewives (OR: 2.8; 95%CI: 1.1-6.9), nulliparae (OR: 2.8; 95%CI: 1.5-3.6), women with family histories of hypertension (OR: 3.6; 95%CI: 1.6-8.5) and women with histories of hypertension during pregnancy (OR: 7.0; 95%CI: 3.0-16.4).
Conclusion
Risk factors for hypertensive diseases in pregnancy in Maroua, Cameroon seem to include early teenage status, illiteracy, housewife status, nulliparity and family or personal histories of hypertension. The knowledge about the aforesaid factors seems to lay the tracks for its prevention in Cameroon.
Keywords: Hypertension, Pregnancy, Risk factor
Introduction
Hypertensive disorder in pregnancy is a condition in which the pregnant woman presents an elevated blood pressure during pregnancy or puerperium as defined in 1986 by the American College of Obstetricians and Gynecologists and adopted by the World Health Organization (WHO) (1–4). Previous reports defined hypertension in pregnancy as a condition presented with a diastolic blood pressure of at least 90 mmHg or a systolic blood pressure of at least 140 mmHg, or a rise in diastolic blood pressure of at least 15 mmHg or a rise of 30 mmHg in systolic blood pressure (2, 3). In the obstetric condition, the Working Group recently defined hypertension in pregnancy as a condition in which, the diastolic blood pressure is at 90 mmHg or above, or a systolic blood pressure is at 140 mmHg or above (5). Moreover, WHO considers only an elevated value of diastolic blood pressure as a criterion for defining the disorder (3). The disorder complicates 4-10% of pregnancies (6–10). The American College of Obstetricians and Gynecologists and the United Nations Organization recognize four categories of hypertension in pregnancy. These include chronic hypertension, gestational hypertension, preeclampsia/eclampsia, and super-imposed preeclampsia/eclampsia, a condition defined as chronic hypertension complicated by pre-eclampsia/eclampsia (2–4).
Several studies have analyzed the risk factors for hypertensive disorders in pregnancy and the identified risk factors include obesity, a family history of hypertension, alcohol intake, heart failure, stroke and left ventricular hypertrophy and smoking (11–13).
A recent study at the Maroua Provincial Hospital revealed that hypertension in pregnancy was the first cause of maternal death, representing 17.5% of the 63 maternal deaths recorded between 2003 and 2005; however, little is known about the risk factors for hypertension in pregnancy in Cameroon, especially in the Far North Region (14).
The aim of this study was to identify the possible risk factors for hypertensive disorders in pregnancy, in order to propose specific preventive measures for the Far North Cameroon.
Methods
This case-control study evaluates hypertension in pregnancy in Far North Cameroon.
Design and site of the study
This case-control study was undertaken at the Maroua Regional Hospital, Cameroon. This hospital is a second level referral facility for the Far North Region. However, its obstetric care unit has insufficient personnel despite its high workload. During the years 2005-2007, there was one gynecologist, one midwife and six trained nurses assisted by four temporary assistant nurses. About four deliveries were carried out per day. Between 2003 and 2004, there were 3263 deliveries of which 144 (4.41%) were by cesarean section.
Population
In the present study, we considered, women with a diastolic blood pressure of at least 90 mmHg or a systolic blood pressure of at least 140 mmHg to have hypertensive disorder in pregnancy. During the study period (June 2005 to May 2007), we identified 176 cases of hypertension in pregnancy. We excluded 16 (9.1%) cases of twin gestations from our analysis. Among the remaining 160 cases, we excluded 8 women who had chronic hypertension, 152 cases were eventually analysed. For each case of hypertension in pregnancy, about 3 women who followed her in delivery and had no hypertension were retained as the controls. Overall, 414 women were recruited as the controls against 152 cases of the study.
Variables of interest
Data were collected on the socio-economic status (age, marital status, educational level, occupation, residence) of the participants.
Data management
The data were collected, tested and corrected for the study. Information from the files was read into MS Excel sheets, and stored in the database of the Department of Obstetrics and Gynecology of the Maroua Provincial Hospital.
Statistical analysis
Data analysis was performed using EPI Info 3.5.1. The conventional rule of thumb was applied and therefore, the chi2 of heterogeneity was used in comparing the distribution of different obstetrical hypertension risks factors in the two study populations when appropriate. However, if an expected number was less than 5, we used an alternative, Fisher's exact test. Odds ratio with 95% confidence interval was used to appreciate the impact of different variables on the risk of presenting hypertension.
The analysis included means, range, standard deviation and proportions. The univariate analysis was conducted to identify the association of different variables on the risk of presenting hypertension in pregnancy. The multivariate analysis was used taking into account the potential confounding factors. The difference was considered significant if the p-value was less than 0.05.
Results
For a period of two years at the Maroua Regional Hospital, (June 2005 to May 2007), there were 3228 deliveries among which 176 were complicated by hypertension (5.45%). Among the overall 3228 deliveries, 60 had hypertension complicated by seizures (1.86%) but 116 did not (3.59%). Eleven women (6.25%) had elevated blood pressure before the 20th week of gestation.
When compared with women without hypertension, the pregnant patients with hypertension presented no difference regarding marital status (94.7% vs. 95.2%), history of abortion (22.4% vs. 23.9%) or history of premature delivery (1.8% vs. 1.7%). Meanwhile, women with hypertensive disorder in pregnancy were at early teenage years (16.4% vs. 6.8%) and in nulliparous status (71.1% vs. 57%) compared to control women. The illiteracy rate was also higher among the women with hypertension disorder (48.7% vs. 35.7%) (Table 1).
Table 1.
Classification of patients according to their socio-demographic and reproductive characteristics
| Socio-demographic and reproductive characteristics | Preeclampsia/eclampsia N = 152, N (%) | No hypertension N = 414, N (%) | Total N = 566, N (%) | P-value |
|---|---|---|---|---|
| Age: Mean (SD) (Range) | 23.5 (7.1) (14-42) | 24.3 (6.4) (13-43) | ||
|
| ||||
| Age (groups) | ||||
| 10-16 years | 25 (16.4) | 28 (6.8) | 53 (9.4) | 0.0128 |
| 17-19 years | 32 (21.1) | 82 (19.8) | 114 (20.1) | |
| 20-24 years | 32 (21.1) | 117 (28.3) | 149 (26.3) | |
| 25-29 years | 32 (21.1) | 92 (22.2) | 124 (21.9) | |
| 30-34 years | 12 (7.8) | 45 (10.8) | 57 (10.1) | |
| 35-44 years/ others | 19 (12.5) | 50 (12.1) | 69 (12.2) | |
| Marital status | ||||
| Married | 144 (94.7) | 394 (95.3) | 538 (95.0) | 0.83 |
| Others | 8 (5.3) | 20 (4.7) | 28 (5.0) | |
| Husband | ||||
| Unmarried | 7 (4.6) | 16 (3.9) | 23 (4.0) | 0.8169 |
| Polygamous | 38 (25.0) | 96 (23.2) | 134 (23.7) | |
| Monogamous | 107 (70.4) | 302 (72.9) | 409 (72.3) | |
| Education level | ||||
| None | 74 (48.7) | 148 (35.7) | 222 (39.2) | 0.0127 |
| Primary | 38 (25.0) | 147 (35.6) | 185 (32.7) | |
| Secondary/ University | 40 (26.3) | 119 (28.7) | 159 (28.1) | |
| Socio-professional group | ||||
| Housewife | 142 (93.5) | 360 (87.0) | 502 (88.7) | 0.0313 |
| Salary owne/ others | 10 (6.5) | 54 (13.0) | 64 (11.3) | |
| History of ectopic pregnancy | ||||
| Yes | 4 (2.6) | 7 (1.7) | 11 (1.9) | 0.496* |
| No | 148 (97.4) | 407 (98.3) | 555 (98.1) | |
| History of abortion | ||||
| Yes | 34 (22.4) | 99 (23.9) | 133 (23.5) | 0.7008 |
| No | 118 (77.6) | 315 (76.1) | 433 (76.5) | |
| Number of deliveries | ||||
| 0 | 108 (71.1) | 236 (57.0) | 344 (60.7) | < 0.001 |
| 1 | 21 (13.8) | 122 (29.5) | 143 (25.3) | |
| ≥ 2 | 23 (15.1) | 56 (13.5) | 79 (14.0) | |
| History of premature delivery | ||||
| No | 149 (98.0) | 407 (98.3) | 556 (98.2) | 0.732* |
| Yes | 3 (1.8) | 7 (1.7) | 10 (1.8) | |
Fisher exact test
The number of patients with hypertensive disease in pregnancy was significantly greater in pregnancy when taking into account a personal history of hypertension in pregnancy (14.5% vs.2.2%), a personal history of chronic hypertension (5.3% vs.1.0%), a history of paternal hypertension (17.8% vs. 6.5%), or a history of hypertension for siblings (8.6% vs. 2.9%) (Table 2). No statistically significant differences were found between the two groups concerning the history of maternal hypertension.
Table 2.
Classification of patients according to the personal and family history of hypertension
| History of hypertensive disease | Preeclampsia/eclampsia N = 152, N (%) | No hypertension N = 414, N (%) | Total N = 566, N (%) | P-value |
|---|---|---|---|---|
| History of maternal hypertension | ||||
| Yes | 14 (9.2) | 20 (4.8) | 34 (6.0) | 0.0519 |
| No | 138 (90.8) | 394 (95.2) | 532 (94.0) | |
| History of brother/sister hypertension | ||||
| Yes | 13 (8.6) | 12 (2.9) | 25 (4.4) | 0.0037 |
| No | 139 (91.4) | 402 (97.1) | 541(95.6) | |
| History of paternal hypertension | ||||
| Yes | 27 (17.8) | 27 (6.5) | 54 (9.5) | <0.0001 |
| No | 125 (82.2) | 387 (93.5) | 512 (90.5) | |
| History of hypertension in pregnancy | ||||
| Yes | 22 (14.5) | 9 (2.2) | 31 (5.5) | <0.0001 |
| No | 130 (85.5) | 405 (97.8) | 535 (94.5) | |
| History of chronic hypertension | ||||
| Yes | 8 (5.3) | 4 (1.0) | 12 (2.1) | 0.0041* |
| No | 144 (94.7) | 410 (99.0) | 554 (97.9) | |
Fisher's exact test
Univariate analysis revealed (Table 3) a greater risk of having hypertension during pregnancy for the age group 13-16 years (OR: 2.6; 95%CI: 1.5-4.7; p= 0.0005), women without any school education (OR: 1.7; 95%CI: 1.1-2.4; p= 0.0052), housewives (OR: 2,8; 95%CI: 1.05-4.2; p= 0.0313), women with no previous deliveries (OR: 1.8; 95%CI: 1.2-2.7; p= 0.0024), women with histories of paternal hypertension (OR: 3.0; 95%CI: 1.7-5.4; p< 0.0001), women with histories of sibling hypertension (OR: 3.1; 95%CI: 1.3-7.0; p= 0.0037), women with histories of hypertension in pregnancy (OR: 7.6; 95%CI: 3.4-16.9; p< 0.0001), and women with histories of chronic hypertension (OR: 5.6; 95%CI: 1.6-19.1; p= 0.0016).
Table 3.
Risk factors for developing hypertensive disorders in pregnancy
| Variables | Total number of women (N) | Preeclampsia/ Eclampsia (N = 152) | Rate (%) | (Odds Ratio)* (95% CI) | P-value | (Odds Ratio)** (95% CI) | P-valuex |
|---|---|---|---|---|---|---|---|
| Age | |||||||
| 20-43 years | 509 | 127 | 25.0 | 1c | 0.0005 | 1c | - |
| 13-16 years | 53 | 25 | 47.2 | 2.6* (1.5 - 4.7) | - | ||
| Education level | |||||||
| Others | 344 | 78 | 22.7 | 1c | 0.0052 | 1c | 0.0177 |
| None | 222 | 74 | 33.3 | 1.7* (1.1 – 2.4) | 1.6b (1.0 – 2.3) | ||
| Socioprofessional group | |||||||
| Others | 64 | 10 | 15.6 | 1c | 0.0313 | 1c | 0.0167 |
| Housewife | 502 | 142 | 28.3 | 2.8* (1.05 – 4.2) | 2,8d (1,1-6,9) | ||
| Number of deliveries | |||||||
| ≥ 1 | 222 | 44 | 19.8 | 1c | 0.0024 | 1c | 0.0001 |
| No delivery | 344 | 108 | 31.4 | 1.8* (1.2 - 2.7) | 2.8e (1.5 - 3.6) | ||
| History of paternal hypertension | |||||||
| No | 512 | 125 | 24.4 | 1c | 0.0000 | 1c | - |
| Yes | 54 | 27 | 50.0 | 3.0* (1.7 – 5.4) | - | ||
| History of brother/sister hypertension | |||||||
| No | 541 | 139 | 25.7 | 1c | 0.0037 | 1c | 0.0014 |
| Yes | 25 | 13 | 52.0 | 3.1* (1.3 – 7.0) | 3.6f (1.6 – 8.5) | ||
| History of hypertension in pregnancy | |||||||
| No | 535 | 130 | 24.3 | 1c | 0.0000 | 1c | 0.0000 |
| Yes | 31 | 22 | 71.0 | 7.6* (3.4 - 16.9) | 7.0g (3.0 - 16.4) | ||
| History of chronic hypertension | |||||||
| No | 554 | 144 | 26.0 | 1c | 0.0016 | 1c | 0.2242 |
| Yes | 12 | 8 | 66.7 | 5.6* (1.6 – 19.1) | 2.0h (0.5 – 7.5) | ||
Non adjusted OR
Adjusted OR
reference category
adjusted on socio-professional group
adjusted on level of education, number of deliveries, history of hypertension in siblings, history of hypertension in pregnancy
adjusted on continuous age and number of deliveries
adjusted on socio-professional group, history of hypertension in pregnancy, history of chronic hypertension
adjusted on education level
adjusted on number of deliveries, history of chronic hypertension
adjusted on socio-professional group, history of paternal hypertension, history of hypertension in pregnancy
At multivariate analysis and after adjustment for different factors linked to the occurrence of hypertension, the risk of having hypertension during pregnancy remained greater for women without any school education (OR: 1.6; 95%CI: 1.0-2.3; p= 0.0117); housewives (OR: 2.8; 95%CI: 1.1-6.9; p= 0.0167); women with no previous deliveries (OR: 2.8; 95%CI: 1.5-3.6; p= 0.0001); women with histories of sibling hypertension (OR: 3.6; 95%CI: 1.6-8.5; p= 0.0014) and women with histories of hypertension in pregnancy (OR: 7.0; 95%CI: 3.0-16.4; p< 0.0001).
Discussion
We conducted this study in order to identify the possible risk factors for hypertensive disorders in pregnancy in Maroua, Cameroon. We found that, the risk factors for hypertensive diseases in pregnancy in Maroua, Cameroon included early teenage status, illiteracy, housewife status, nulliparity, and family and the personal histories of hypertension.
The extreme ages of reproductive years are well-known risk factors for hypertension during pregnancy with high incidence rates in teenagers (15, 16).
Many authors have identified young age as a risk factor for hypertension during pregnancy, as is the case in the present study (17, 18). Adeyinka et al. found the prevalence of eclampsia and pre-eclampsia among adolescents to be 20% in comparison to only 3.33% among the controls (17). In another study, a 2.9% vs. 0.6% preeclampsia prevalence was reported in teenagers compared to women aged 25-34 years (18). In the present study, the number of early teenagers among patients with hypertension was 16.4% compared to 6.8% among the controls. We found that early teenage status (13-16 years) was associated with an increased risk for hypertensive disorders in pregnancy (OR: 2.6; 95%CI: 1.5-4.7; p= 0.0005). Similar findings were reported by Saftlas et al. (16) who revealed that black teenagers aged 15-17 years had 2.6-fold risk for preeclampsia compared to women aged 24-34 years.
Studies have reported that a higher age is also an important risk factor for hypertension in pregnancy, especially in developed countries (19, 20). Assis et al. (20) found that age above 30 years was associated with a risk for preeclampsia super-imposed on chronic hypertension (OR: 5.218; 95% CI: 1.873 to 14.536) (20). A similar result was reported by Suzuki et al. (19) who found that, in singleton pregnancies, the developing pre-eclampsia was associated with maternal age 35 years or above. Both studies reported the association of infertility treatment with an increased risk for hypertensive disorders in pregnancy as this was also recently reported by Poon et al. (21), but Maroua, Cameroon is a semi-urban area and few women are likely to be under ovulation treatment.
In the present study, the percentage of women aged 35 to 44 years old was similar in the two study populations revealing that, this age group was not associated with an increased risk of hypertensive disorders in pregnancy. Some studies are necessary to understand better why there is lack of effect of the age progress on the occurrence of hypertensive disorders in pregnancy.
The absence of previous deliveries is widely reported as a risk factor for hypertensive disorders in pregnancy (19, 22, 23). Assis et al. (20) identified primiparity as a risk factor for gestational hypertension (OR: 5.435; 95% CI: 1.9-15.4). In the present study, we found that nulliparity was associated with a nearly 2-fold risk for hypertensive disorders in pregnancy (OR: 1.8; 95% CI: 1. 2-2.7). Our findings are in conformity with the aforementioned literature reports.
In the present study, women with at least two previous deliveries represented 15.1% vs. 13% when respectively comparing hypertensive to non- hypertensive women. Previous studies did find multiparity as a risk factor for hypertension in pregnancy, however, they reported an increased risk the nulliparous women had a different partner (24, 25).
We found that illiteracy was associated with about 2-fold risk for presenting hypertensive disorder in pregnancy (OR: 1.7; 95% CI: 1.1-2.4). The absence of school education, identified as an independent risk factor for hypertensive disorder in pregnancies, is well-documented in the literature (26, 27). Among the risk factors for pre-eclampsia Mittendorf et al. (28) identified less than a high school education (OR: 2.0, 95% CI: 1.1-3.6). The illiteracy rate in our population could influence the occurrence of hypertension in pregnancy by the simple reason that the low school level is associated indirectly to the precocious marriage and to limited access to health care, including family planning.
Even though some authors have not found any difference in pregnancy outcomes between housewives and employed women (29), most publications state that workers have adverse outcomes (30–32). In the present study, housewives had an increased risk for hypertensive disorder in pregnancy (OR: 2.8; 95% CI: 1.05-4.2). However, housewives, respectively, represent 93.4% and 87% in hypertensive and non-hypertensive study populations and could randomly influence the pregnancy risks.
Hypertension during pregnancy is also known to be an important risk factor for developing hypertension in pregnancy (23). Previous pre-eclampsia as an independent risk for super-imposed preeclampsia was reported to be associated with about 5-fold increase for the risk (OR: 4.757; 95% CI: 1.261-17.938). A higher risk of hypertensive disorder in pregnancy was reported among women with previous hypertension in pregnancy (OR: 7.6; 95% CI: 3.4-16.9) (20).
Personal history of chronic hypertension is one of the reported risk factors for hypertensive diseases in pregnancy (21, 33). Family history of hypertension was identified as a risk factor for hypertension in Cameroon (11). However, little is known separately about histories of paternal, sibling or maternal hypertension, although we were able to illustrate that the last one is not a risk factor for hypertensive disease in pregnancy.
Some studies have reported body mass index and birth spacing as risk factors for hypertension in pregnancy, but those variables were not analyzed in the present study (34, 35).
Conclusion
Risk factors for hypertensive diseases in pregnancy in Maroua, Cameroon included early teenage status, illiteracy, housewife status, nulliparity, and family and personal histories of hypertension. Knowledge of risk factors for hypertensive disorders in pregnancy may give tracks for prevention in the population of Maroua, Cameroon and beyond. Some more extended prospective studies are necessary to confirm our findings. The confirmation of these findings should help towards the development of the national strategies of hypertension in pregnancy prevention. Prevention must include campaigns and education from the medical and paramedical staff.
Acknowledgement
Authors declare no conflict of interest.
To cite this article: Tebeu PM, Foumane P, Mbu R, Fosso G, Biyaga P T, Fomulu JN. Risk actors for Hypertensive Disorders in Pregnancy: A Report from the Maroua Regional ospital, Cameroon. J Reprod Infertil. 2011;12(3):227-234.
References
- 1.ACOG. ACOG technical bulletin. Hypertension in pregnancy. Number 219--January 1996 (replaces no. 91, February 1986). Committee on Technical Bulletins of the American College of Obstetricians and Gynecologists. Int J Gynaecol Obstet. 1996;53(2):175–83. [PubMed] [Google Scholar]
- 2.Cunningham FG, Leveno KJ, Bloom SL, Hauth JC, Gilstrap LC, III, Wenstrom KD. Hypertensive disorders in pregnancy. 22nd ed. USA: McGraw-Hill Companies Inc; 2005. Williams Obstetrics; pp. 426–50. Chapter 34. [Google Scholar]
- 3.McCaw Binns AM, MacGillivray I, Hawkins N, Golding J, Ashley DEC. International variation in the incidence of hypertension in pregnancy among primiparae: the Jamaican experience. West Indian Med J. 1997;46(Suppl 2):29. [Google Scholar]
- 4.Schroeder BM. American College of Obstetricians and Gynecologists. ACOG practice bulletin on diagnosing and managing preeclampsia and eclampsia. American College of Obstetricians and Gynecologists. Am Fam Physician. 2002;66(2):330–1. [PubMed] [Google Scholar]
- 5.Working Group on High Blood Pressure. Report of the National High Blood Pressure Education Program Working Group on High Blood Pressure in Pregnancy. Am J Obstet Gynecol. 2000;183(1):S1–S22. [PubMed] [Google Scholar]
- 6.Roberts CL, Algert CS, Morris JM, Ford JB, Henderson-Smart DJ. Hypertensive disorders in pregnancy: a population-based study. Med J Aust. 2005;182(7):332–5. doi: 10.5694/j.1326-5377.2005.tb06730.x. [DOI] [PubMed] [Google Scholar]
- 7.Golding J. A randomised trial of low dose aspirin for primiparae in pregnancy. The Jamaica Low Dose Aspirin Study Group. Br J Obstet Gynaecol. 1998;105(3):293–9. doi: 10.1111/j.1471-0528.1998.tb10089.x. [DOI] [PubMed] [Google Scholar]
- 8.Levine RJ, Hauth JC, Curet LB, Sibai BM, Catalano PM, Morris CD, et al. Trial of calcium to prevent preeclampsia. N Engl J Med. 1997;337(2):69–76. doi: 10.1056/NEJM199707103370201. [DOI] [PubMed] [Google Scholar]
- 9.Conde-Agudelo A, Belizán JM. Risk factors for pre-eclampsia in a large cohort of Latin American and Caribbean women. BJOG. 2000;107(1):75–83. doi: 10.1111/j.1471-0528.2000.tb11582.x. [DOI] [PubMed] [Google Scholar]
- 10.Trogstad LI, Eskild A, Magnus P, Samuelsen SO, Nesheim BI. Changing paternity and time since last pregnancy; the impact on pre-eclampsia risk. A study of 547 238 women with and without previous pre-eclampsia. Int J Epidemiol. 2001;30(6):1317–22. doi: 10.1093/ije/30.6.1317. [DOI] [PubMed] [Google Scholar]
- 11.Shey Wiysonge CU, Ngu Blackett K, Mbuagbaw JN. Risk factors and complications of hypertension in Yaounde, Cameroon. Cardiovasc J S Afr. 2004;15(5):215–9. [PubMed] [Google Scholar]
- 12.Pridjian G, Puschett JB. Preeclampsia. Part 1: clinical and pathophysiologic considerations. Obstet Gynecol Surv. 2002;57(9):598–618. doi: 10.1097/00006254-200209000-00023. [DOI] [PubMed] [Google Scholar]
- 13.Leeners B, Rath W, Kuse S, Irawan C, Imthurn B, Neumaier-Wagner P. BMI: new aspects of a classical risk factor for hypertensive disorders in pregnancy. Clin Sci (Lond) 2006;111(1):81–6. doi: 10.1042/CS20060015. [DOI] [PubMed] [Google Scholar]
- 14.Tebeu PM, Ngassa P, Kouam L, Major AL, Fomulu JN. Maternal mortality in Maroua Provincial Hospital, Cameroon (2003-2005) West Indian Med J. 2007;56(6):502–7. [PubMed] [Google Scholar]
- 15.Chesley LC. History and epidemiology of pre-eclampsia-eclampsia. Clin Obstet Gynecol. 1984;27(4):801–20. doi: 10.1097/00003081-198412000-00004. [DOI] [PubMed] [Google Scholar]
- 16.Saftlas AF, Olson DR, Franks AL, Atrash HK, Pokras R. Epidemiology of preeclampsia and eclampsia in the United States, 1979-1986. Am J Obstet Gynecol. 1990;163(2):460–5. doi: 10.1016/0002-9378(90)91176-d. [DOI] [PubMed] [Google Scholar]
- 17.Adeyinka DA, Oladimeji O, Adekanbi TI, Adeyin-ka FE, Falope Y, Aimakhu C. Outcome of adolescent pregnancies in southwestern Nigeria: a case-control study. J Matern Fetal Neonatal Med. 2010;23(8):785–9. doi: 10.3109/14767050903572166. [DOI] [PubMed] [Google Scholar]
- 18.Usta IM, Zoorob D, Abu-Musa A, Naassan G, Nassar AH. Obstetric outcome of teenage pregnancies compared with adult pregnancies. Acta Obstet Gynecol Scand. 2008;87(2):178–83. doi: 10.1080/00016340701803282. [DOI] [PubMed] [Google Scholar]
- 19.Suzuki S, Igarashi M. Risk factors for preeclampsia in Japanese twin pregnancies: comparison with those in singleton pregnancies. Arch Gynecol Obstet. 2009;280(3):389–93. doi: 10.1007/s00404-009-0932-4. [DOI] [PubMed] [Google Scholar]
- 20.Assis TR, Viana FP, Rassi S. Study on the major maternal risk factors in hypertensive syndromes. Arq Bras Cardiol. 2008;91(1):11–7. doi: 10.1590/s0066-782x2008001300002. [DOI] [PubMed] [Google Scholar]
- 21.Poon LC, Kametas NA, Chelemen T, Leal A, Nicolaides KH. Maternal risk factors for hypertensive disorders in pregnancy: a multivariate approach. J Hum Hypertens. 2010;24(2):104–10. doi: 10.1038/jhh.2009.45. [DOI] [PubMed] [Google Scholar]
- 22.Jacobs DJ, Vreeburg SA, Dekker GA, Heard AR, Priest KR, Chan A. Risk factors for hypertension during pregnancy in South Australia. Aust N Z J Obstet Gynaecol. 2003;43(6):421–8. doi: 10.1046/j.0004-8666.2003.00120.x. [DOI] [PubMed] [Google Scholar]
- 23.Kimbally KG, Barassoumbi H, Buambo SF, Gombet T, Kibeke P, Monabeka HG, et al. Arterial hypertension: epidemiological aspects and risk factors on pregnant and delivered woman] Dakar Med. 2007;52(2):148–52. French. [PubMed] [Google Scholar]
- 24.Li DK, Wi S. Changing paternity and the risk of preeclampsia/eclampsia in the subsequent pregnancy. Am J Epidemiol. 2000;151(1):57–62. doi: 10.1093/oxfordjournals.aje.a010122. [DOI] [PubMed] [Google Scholar]
- 25.Trupin LS, Simon LP, Eskenazi B. Change in paternity: a risk factor for preeclampsia in multi-paras. Epidemiology. 1996;7(3):240–4. doi: 10.1097/00001648-199605000-00004. [DOI] [PubMed] [Google Scholar]
- 26.Silva LM, Coolman M, Steegers EA, Jaddoe VW, Moll HA, Hofman A, et al. Low socioeconomic status is a risk factor for preeclampsia: the Generation R Study. J Hypertens. 2008;26(6):1200–8. doi: 10.1097/HJH.0b013e3282fcc36e. [DOI] [PubMed] [Google Scholar]
- 27.Silva L, Coolman M, Steegers E, Jaddoe V, Moll H, Hofman A, et al. Maternal educational level and risk of gestational hypertension: the Generation R Study. J Hum Hypertens. 2008;22(7):483–92. doi: 10.1038/jhh.2008.22. [DOI] [PubMed] [Google Scholar]
- 28.Mittendorf R, Lain KY, Williams MA, Walker CK. Preeclampsia. A nested, case-control study of risk factors and their interactions. J Reprod Med. 1996;41(7):491–6. [PubMed] [Google Scholar]
- 29.Najman JM, Morrison J, Williams GM, Andersen MJ, Keeping JD. The employment of mothers and the outcomes of their pregnancies: an Australian study. Public Health. 1989;103(3):189–98. doi: 10.1016/s0033-3506(89)80074-5. [DOI] [PubMed] [Google Scholar]
- 30.Jansen PW, Tiemeier H, Verhulst FC, Burdorf A, Jaddoe VW, Hofman A, et al. Employment status and the risk of pregnancy complications: the Generation R Study. Occup Environ Med. 2010;67(6):387–94. doi: 10.1136/oem.2009.046300. [DOI] [PubMed] [Google Scholar]
- 31.El-Gilany AH, El-Wehady A, El-Hawary A. Maternal employment and maternity care in Al-Hassa, Saudi Arabia. Eur J Contracept Reprod Health Care. 2008;13(3):304–12. doi: 10.1080/13625180802185080. [DOI] [PubMed] [Google Scholar]
- 32.Bao Y, Hu Y, Fu S, Zhang J, Zhang F, Wang X. Studies on relationship between occupation and pregnancy outcome] Zhonghua Yu Fang Yi Xue Za Zhi. 1999;33(1):30–3. Chinese. [PubMed] [Google Scholar]
- 33.Craici I, Wagner S, Garovic VD. Preeclampsia and future cardiovascular risk: formal risk factor or failed stress test? Ther Adv Cardiovasc Dis. 2008;2(4):249–59. doi: 10.1177/1753944708094227. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34.Luealon P, Phupong V. Risk factors of preeclampsia in Thai women. J Med Assoc Thai. 2010;93(6):661–6. [PubMed] [Google Scholar]
- 35.Hjartardottir S, Leifsson BG, Geirsson RT, Stein-thorsdottir V. Paternity change and the recurrence risk in familial hypertensive disorder in pregnancy. Hypertens Pregnancy. 2004;23(2):219–25. doi: 10.1081/PRG-120037889. [DOI] [PubMed] [Google Scholar]