Obstructive Sleep apnea (OSA) is a common and underdiagnosed condition in obese pregnant women with serious and life-threatening complications to the mother and baby. The investiators propose that a non-invasive method may be used to detect patients at risk of OSA, giving these women access to the necessary treatment to treat this condition. The method is a estimation of body water, which has been shown to be linked to OSA in the non-pregnant population. Body water is estimated by applying surface electrodes to a participant who is lying down by measuring bioimpedance through body tissues by applying a tiny current between the electrodes. The electrical stimulation is not felt by the participant and has no negative effects on mother or baby.

It is already established that the increasingly prevalent condition of obesity is linked to OSA in pregnancy. Obesity is increasingly prevalent This study will evaluate a novel method of screening for OSA in the obese pregnant population, thereby treating this condition reducing the ill effects to mother and fetus.

This will be a prospective observational cohort study. Eligible participants will be approached for consent during their third-trimester antenatal all-day clinic visit. Body water will be measured by connecting electrodes to participants hands, feet and neck whilst lying supine for approximately 15 minutes.

Data on patient demographics, BMI, medical conditions, water body composition and indicators of OSA (breathing pattern and oxygen levels during sleep) will be collected, as well as data from patients' sleep tests as ordered by their physician.

Inclusion Criteria:

• Participants who give written informed consent
• Pregnant women in the third trimester of pregnancy
• Grade III obesity
• Patients who have prior diagnosis of OSA within the last one year, and non-compliant to treatment such as continuous positive airway pressure (CPAP), or dental appliance
• Patients suspected to have OSA based on screening questionnaire (see page 2, OSA-Diagnostic tools for further details)

Exclusion Criteria:

• Fluid overload states including renal disease, liver disease and congestive heart failure
• Prior history of vascular surgery in the lower limbs such as varicose vein surgery, vascular by-pass surgery or evidence of venous efficiency.
• Patients with metal implants in lower limbs or spine, due to possible interference with the leg impedance signals. 58
• Participants with diagnosed OSA treated with Continuous Positive Airway Pressure (CPAP).
• Patients requiring urgent sleep physician referral (within four weeks) due to serious medical conditions or safety critical-occupations according to the 2011 Canadian Thoracic Society (CTS) guideline 59 e.g. unstable ischemic heart disease, recent cerebrovascular disease.
• Implantable cardiac devices

Eligible participants will be approached for consent at our high risk maternal and infant program clinic on the day of their regularly scheduled appointment.