Seeing the scale stop or drop during the final weeks of pregnancy can be unexpected and cause worry. While most of pregnancy involves consistent weight gain, a change in this pattern late in the third trimester is a common concern. Weight loss or a plateau can sometimes signal underlying issues, but it is often a normal physiological shift as the body prepares for labor. Understanding the reasons helps distinguish between a typical late-stage fluctuation and a concern requiring medical attention.
Understanding Normal Third Trimester Weight Changes
The third trimester, starting around week 28, typically involves a significant increase in weight as the fetus undergoes its most rapid growth phase. On average, a person gains approximately 0.5 to 1 pound per week, contributing to a total third-trimester gain of about 9 to 13 pounds. This weight accounts for the growing baby, the placenta, increased blood volume, and maternal fat stores.
As the due date approaches (weeks 36 to 40), this rate of gain frequently slows down dramatically or stops entirely. In the final one or two weeks before delivery, a slight dip in weight, usually 1 to 3 pounds, is commonly observed. This minor weight reduction is considered a normal sign that the body is making final preparations for labor and should not be confused with a significant, sudden loss.
Common Physiological Factors Contributing to Weight Stagnation or Loss
The slight weight drop in late pregnancy is usually a temporary reflection of fluid and physical adjustments rather than a loss of overall tissue mass. One major factor is “lightening,” or the engagement of the baby’s head deeper into the pelvis. This downward shift relieves upward pressure on the stomach and diaphragm, which can increase comfort during meals, though it changes fluid dynamics.
Fluid redistribution plays a significant role, as the body begins to shed excess water retention built up earlier in the pregnancy. This process manifests as increased urination, heightened perspiration, and sometimes more frequent bowel movements, all contributing to a temporary reduction in scale weight. Furthermore, the volume of amniotic fluid peaks around 34 to 36 weeks and naturally begins to decrease as the pregnancy progresses toward term.
Another contributing factor is a reduced capacity for large meals due to the size of the growing uterus. Even if appetite remains normal, physical compression of the stomach often forces the mother to eat smaller, more frequent meals. This can lead to a slight caloric shortfall, contributing to the benign weight plateau or minor loss seen in late-term pregnancies.
Underlying Medical Causes Requiring Attention
While a slight weight drop is often normal, a significant, rapid, or sustained weight loss in the third trimester can indicate an underlying medical concern that warrants immediate investigation. Conditions causing severe and persistent nausea or vomiting, such as late-onset hyperemesis gravidarum, can lead to inadequate calorie intake and dehydration. This compromises both maternal nutrition and the baby’s growth.
Uncontrolled gestational diabetes can sometimes present with maternal weight loss despite high caloric intake, as the body struggles to process and utilize glucose effectively. The mother is not adequately absorbing nutrients. Preeclampsia, characterized by high blood pressure, typically causes rapid fluid shifts and sudden swelling, but in rare, severe cases, it may be linked to metabolic changes affecting weight.
A sudden, unexplained drop in maternal weight may also signal insufficient fetal growth, known as Intrauterine Growth Restriction (IUGR). While IUGR is often linked to placental issues, persistent maternal malnutrition or a serious underlying illness can contribute, restricting the baby’s ability to gain weight and thrive. These medical causes usually present with other distinct symptoms, such as severe headaches, vision changes, or high blood pressure.
Monitoring and Consultation Guidelines
The most responsible action when observing any unexpected weight change is to communicate the finding to your healthcare provider promptly. Track your weight, noting how much was lost and the timeframe over which it occurred, to provide accurate data. Maintaining a simple log of food and fluid intake can also help your provider assess your nutritional status.
Contact your doctor immediately if the weight loss is sudden and substantial, such as more than 5 pounds in a short period. Decreased fetal movement is an urgent warning sign that accompanies weight loss and is a significant concern at any point in the third trimester.
Urgent Warning Signs
Symptoms that must prompt an immediate call to your medical team include:
- Persistent, severe vomiting.
- Fever.
- Intense abdominal pain.
- Any visual disturbances.
Even if the weight loss seems minor, a medical review is necessary to confirm that fetal growth remains appropriate and that the mother’s health is stable.