Page ContentObesity and PregnancyFirst Trimester | Second Trimester | Third Trimester | Postpartum Body mass index, or BMI, is based on a simple math formula (weight divided by height squared) to determine whether an individual is at a healthy weight. A BMI over 25 is considered overweight. BMI over 30 is considered obese. You and your doctor will determine your BMI during your first visit. Obesity during pregnancy puts you at risk for several health problems:Gestational diabetes (diabetes first diagnosed during pregnancy)Preeclampsia (high blood pressure disorder) Sleep apnea (a sleep disorder that causes a person to stop breathing periodically during sleep) Obesity increases the risks of the following problems during pregnancy:Miscarriage Birth defects of the heart and developing spinal cord Difficulty obtaining accurate results from ultrasounds and fetal monitoring Fetal macrosomia- an abnormal extra growth pattern of the baby Preterm birth Stillbirth Cesarean delivery (C-section) or complications in childbirth Losing weight BEFORE you become pregnant is the best way to decrease the risk of problems caused by obesity. Losing even a small amount of weight (5 to 7% of your current weight, or about 10 to 20 pounds) can improve your overall health and pave the way for a healthier pregnancy.