Weight loss or a plateau in weight gain during the third trimester can be concerning, especially after months of steady weight gain. While this change is sometimes a normal physiological fluctuation, it always warrants attention. Understanding the mechanisms at play in the late stages of gestation helps distinguish between a natural change and a sign of a more serious issue. This knowledge ensures both maternal and fetal well-being before delivery.
Common Physiological Reasons for Late-Stage Weight Stalling
Weight stabilization or a slight dip near the end of pregnancy is often caused by shifts in the mother’s body fluids and appetite. As the body prepares for labor, it begins to shed excess fluid retained throughout the preceding months. This process results in increased urination and sometimes heightened perspiration, accounting for a small but noticeable reduction in “water weight.”
The growing uterus occupies a significant portion of the abdominal cavity, exerting pressure upward on the stomach and other digestive organs. This physical compression reduces the stomach’s capacity, causing a feeling of fullness after eating only small amounts of food. This often results in a temporary decrease in overall caloric intake.
The mother’s body may also burn calories at a faster rate due to increased metabolic demands. Furthermore, the final weeks can trigger a “nesting” instinct, leading to bursts of increased physical activity and energy expenditure. When this increased caloric burn slightly outpaces the mother’s reduced intake, the scale may reflect a minor loss.
When Weight Loss Signals a Potential Complication
Weight loss can signal an underlying medical condition, though it is rarely the sole indicator of a problem. The most concerning cause is a recurrence of hyperemesis gravidarum, characterized by severe and continuous vomiting. This condition leads to dehydration, electrolyte imbalances, and weight loss exceeding five percent of the pre-pregnancy weight, necessitating immediate medical intervention.
Preeclampsia is typically marked by new-onset high blood pressure and protein in the urine after 20 weeks, and is usually associated with sudden, excessive weight gain due to fluid retention. However, if the mother experiences severe, persistent nausea and vomiting as a symptom of preeclampsia, or if she has an underlying thyroid issue, weight loss can occur. Serious signs of preeclampsia to monitor are severe headaches, vision changes like seeing spots, and intense upper right abdominal pain.
Weight loss can also be a secondary concern related to Fetal Growth Restriction (FGR), where the fetus is not growing at the expected rate due to issues like placental insufficiency. While inadequate maternal weight gain or weight loss in the third trimester is linked to a higher risk of FGR, the condition is not diagnosed by the mother’s weight. FGR is primarily detected through routine prenatal measurements, such as fundal height falling behind the expected curve, and confirmed through ultrasound examinations.
Steps to Take When Monitoring Weight Changes
If you notice a sudden drop or a prolonged plateau in your weight, contact your healthcare provider immediately for a comprehensive evaluation. This conversation should include details about the amount of weight lost and any other symptoms you may be experiencing. It is helpful to track your food and fluid intake for a few days before your appointment, noting any episodes of nausea or vomiting.
The most direct and actionable way to monitor the well-being of the fetus is through daily fetal movement counts, or “kick counts.” A change in the baby’s usual pattern or a significant decrease in movement is a much more reliable indicator of fetal distress than the mother’s weight. Healthcare providers generally recommend tracking the time it takes to feel ten distinct movements, and any deviation from the baby’s normal activity level requires urgent medical attention.
Prioritize eating small, nutrient-dense meals frequently throughout the day to counteract the physical compression of the stomach. Attempting to drastically increase caloric intake or change your diet without professional guidance is not recommended. Your provider will assess your overall health and may recommend additional testing, such as blood work or a non-stress test, to ensure both you and your baby remain healthy for the final phase of pregnancy.