This is an open-label multicenter randomized-controlled trial in 3 tertiary care hospitals including Ramathibodi Hospital, Phramongkutklao Hospital and Rajavithi Hospital. The study involved screening of obstructive sleep apnea in high risk pregnancy during 1st and 2nd trimesters. Randomization to either continuous positive airway pressure (CPAP) or usual antenatal care (ANC) until delivery will be done. Efficacy of CPAP on pregnancy outcome will be analysed.

Screening for sleep disordered breathing (Respiratory disturbance index, RDI ≥ 5 events/hour) with type 2 sleep test will be performed in eligible subjects during early1st trimester (<16 weeks). Repeat sleep study will be done if the RDI in 1st trimester is less than 5. If the subjects meet the inclusion criteria without any of the exclusion criteria, randomization into either receiving CPAP treatment or usual ANC will be done. The pressure of CPAP machine is determined using autoCPAP machine algorithm at 90 percentile. Adjustment of CPAP machine is repeated at 24-28 week gestations. Subjects in both groups received standard usual care during ANC and outcomes were measured with similar case record forms.

High risk pregnant women attending the antenatal care at the collaborated hospitals will be eligible for the study if they meet all following inclusion criteria.

Inclusion criteria (ALL criteria)

1. Singleton pregnant women age ≥ 18 years

2. Pregnant women attending the antenatal care and intending to deliver at one of the study hospitals with gestational age < 16 weeks

3. Thai nationality with ability to use Thai language proficiently both in spoken and written language.

4. Have been diagnosed as high-risk pregnancy by Obstetricians by having any of the following conditions

   1. Chronic hypertension prior to pregnancy
   2. Hypertension during pregnancy before 20 weeks gestation.
   3. Pre-eclampsia/gestational hypertension during recent pregnancy
   4. Obesity defined by pre-pregnancy body mass index (BMI) ≥ 27.5 kg/m2
   5. History of diabetes mellitus or gestational diabetes
   6. Having gestational diabetes or overt diabetes

5. Presence of snoring (either as frequent snoring ≥3 times/week or loud snoring) prior to or occurring during pregnancy OR respiratory disturbance index, RDI ≥ 5 events/hour by type 2 sleep testing at either point of testing during early pregnancy (0-16 GA week) or late pregnancy (GA 24-28week ).

6. Sign written informed consent

Exclusion Criteria:

1. Subjects' unwillingness to participate in the study at any time of the study.
2. Subject with significant medical conditions such as immunocompromised status, chronic infection (HIV infection, tuberculosis), chronic lung and cardiac conditions, chronic renal failure, thyroid disease, or neuromuscular disease.
3. Subjects with extremely severe obstructive sleep apnea (RDI ≥30) or with significant O2 desaturation <80% during sleep that might have potential benefit from the CPAP treatment.
4. Subject with known obstructive sleep apnea and currently on CPAP treatment

Pregnant women

For the first five years after the trial is concluded (upon acceptance of the primary manuscript for publication) the data will remain accessible only to the trial investigators for the purpose of additional analyses and publications. Thereafter other interested researchers may request in writing to the Steering Committee access to the data for the purpose of meta-analyses, with approval of a protocol and signed data access agreement via contacting the principle investigators of Division of Sleep Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand