One of the most important medical issues during pregnancy is gestational hypertension (GH) (1), reported among 10% of pregnant women. It has been associated with different embryonic and maternal complications such as premature birth, post term baby, fetal death, early detachment of placenta, acute liver and kidney failure, pre and postpartum hemorrhages (2).
Women with GH are at an increased risk of seizure during pregnancy, metabolic syndrome, cardiovascular diseases, and stroke (3). Furthermore, GH, bleeding, and infection are considered as the main causes of mortality during pregnancy (4). Prenatal mortality rate in mothers with GH is five times higher than the ones with normal blood pressure (5).
Although some of the main causes of GH are still uncertain, several risk factors, including the number of births, multiple births, weight gain, chronic kidney disease, chronic hypertension, family history, getting new sexual partner, low age of mother at the time of first pregnancy, pregnancy in ≥40 years old, blood incompatibility, living in high-altitude areas, and inappropriate socio-economic status may influence GH (3). Obstructive sleep apnea (OSA) is also a known risk factor for GH (6).
Pregnancy along with many physiological and hormonal changes affect the structure of sleep (2). Reduced sleep quality is one of the common complaints among pregnant women, especially during the third trimester of pregnancy (7).
Sleep breathing disorders is one of the most common types of sleep problems in pregnant women. This disorder is characterized by frequent upper airway obstruction during sleep, abnormal breathing pattern, frequent hypoxia, and arousals from sleep (8). Anthropometric indices, hormones, and differences in the structure of sleep make pre-menopause women less susceptible to sleep apnea when compared with age-matched men (9). However, the physiological and hormonal changes during pregnancy can cause or exacerbate sleep breathing disorders (8). Thirty percent of people with high blood pressure suffer from sleep-disordered breathing (SDB), and 45-68% of patients with respiratory sleep disorders have high blood pressure (10).
SDB in adults refers to cessation of airflow for more than 10 seconds, which may be due to an upper airway obstruction during sleep, and could lead to increased sympathetic activity because of repeated arousals during sleep and hypoxia (11).
The incidence rate of SDB in pregnant women is 3 to 6 times more common than non-pregnant women (12). The symptoms and signs of SDB include habitual snoring, sleep disruption, neck circumference > 16 inches, high blood pressure, feeling tired, feeling not refreshed after sleep during the day, daytime sleepiness, lack of concentration, and personality change (2).
Since pregnant women experience sleep disturbances and have reduced ability to perform more daily tasks than non-pregnant ones, these symptoms are attributed to their pregnancy and subsequently symptoms of SDB may be overlooked in them. Thus, the presence of these symptoms in pregnant women requires more attention by health care providers (2).
Various factors are involved in occurrence and exacerbation of SB in pregnant women, such as decreasing diameter and dimensions of the upper airway due to inflammation and nasal congestion, increased estrogen and progesterone secretion, increased diaphragmatic effort to increase negative pressure in the upper airway, decrease in the functional residual capacity of lung, a higher supine position to accommodate increased uterine volume, respiratory alkalosis, central chemical stimuli induced by increased progesterone levels, and sleeping to the back (13).
Furthermore, SDB is associated with cardiac, respiratory and hemodynamic problems, such as asphyxia, decreased and increased pulse rate, and fluctuations in systemic and pulmonary arteries and cardiac output. This complication is considered as an independent risk factor for high blood pressure (14). It has been proven that there is an association between SDB and high blood pressure, heart failure, atrial fibrillation, myocardial infarction, brain stroke, and sudden cardiac death. Studies have shown that about half of the these patients have high blood pressure and are resistant to blood pressure reducing drugs (15). Pine et al. showed that 26.7% of women in the third trimester of pregnancy suffer from SDB (16).
In the study conducted by Sarberg et al., 7.9% of women in the first trimester and 21.2% of women in the third trimester of pregnancy suffered from sleep apnea (17).
Snoring is one of 7the important symptoms of sleep apnea (7). According to the studies conducted by Bourjeily and O'brien, 35.1% and 34% of women snore in the last trimester of pregnancy, respectively (9, 18).
The obtained results from Sarberg et al. showed that snoring rate increased from 7.9% in the first trimester to 21.2% in the third trimester of pregnancy (17).
Snoring and SDB in pregnant women can lead to intolerance of glucose and gestational diabetes, preeclampsia, maternal depression, unplanned cesarean section, intrauterine growth retardation of fetus, preterm delivery, alpha-phytoprotein levels, and low birth weight (11) .
Screening pregnant women in terms of sleeping problems and consequently performing more specific tests and treatments can reduce the maternal and fetal complications arising from sleep disturbances.
Available data regarding the prevalence of risk factors of OSA in Iran is limited and obstetricians and physicians in charge of pregnant women overlook sleep problems as one of the causes of adverse maternal and fetus outcomes during pregnancy. Thus, considering the importance of SDB and its adverse outcomes on mother and fetus, the present study was conducted to determine the risk factors for OSA and its association with GH rate among the employed pregnant women (19). 
 
 

This analytical and case-control study was carried out in 2016-2017. The participants were divided into two groups: pregnant women with high blood pressure and the ones with normal blood pressure referring to two Imam Khomeini and Baharloo hospitals (affiliated to Tehran University of Medical Sciences) for prenatal care.
The employed women referring to the prenatal or delivery care centers were asked to participate in the study. GH was defined as a blood pressure higher than 140/90 measured on two separate occasions, more than 6 hours apart, without the presence of protein in the urine and diagnosed after 20 weeks of gestation. The inclusion criteria included pregnant employed women with gestational age of more than 20 weeks. Participants with the following criteria were excluded: pre-pregnancy history of hypertension, cardiovascular disease in the mother during and before pregnancy, kidney diseases in the mother during pregnancy and before it.
The participants’ questionnaire comprised of three parts:
1) A demographic characteristics’ questionnaire that was completed for each patient, including age, weight, height, educational level, employment history, and past medical history or disease.
2) Characteristics of participants' pregnancy: gestational age, systolic blood pressure, diastolic blood pressure, and the number of pregnancies.
3) Associated risk factors of OSA using validated STOP-BANG questionnaire in Persian (20), including loud recurring snoring in the sleep, daytime sleepiness, observed apnea during sleep, age >50 years, BMI 35 kg/m², neck circumference > 40 cm, and high blood pressure.
Measurements of height, weight, blood pressure, and neck circumference were performed by the researcher and other questions were asked by interview method.

The study was approved by ethical committee of Tehran University of Medical Sciences, Iran. Oral consent was obtained from all participants.
Collected data were analyzed using SPSS Statistics for Windows, version 16.0 (SPSS Inc., Chicago, Ill., USA). Frequency and percentage were used to describe the data. Data were analyzed using non-parametric Chi-square test. P-value less than 0.05 was considered significant.