Most women have no trouble packing on pounds over the course of their pregnancy. Extra food and calories give your baby the nutrients he needs to grow and allow you to build fat stores for breast feeding. Some women struggle to gain weight for a variety of reasons, including morning sickness, severe nausea and struggles with self-image. Discuss concerns about your weight with your obstetrician.

First Trimester Symptoms

Plenty of women fail to gain weight and even lose weight in the first trimester when pregnancy symptoms are most intense. A combination of morning sickness, nausea, exhaustion, heartburn and constipation may keep you from eating much besides crackers and ginger ale. The American Pregnancy Association recommends a gain of 1 to 4.5 pounds in the first trimester, but you can compensate later in the pregnancy if sickness keeps you from gaining weight.

Hyperemesis Gravidarum

Gain No Weight During Pregnancy Some women experience a very severe form of morning sickness called hyperemesis gravidarum, which results in failure to gain weight and can lead to weight loss. Hyperemesis gravidarum is characterized by severe vomiting, nausea that doesn't subside after the first trimester, vomiting that causes dehydration and inability to tolerate any food. The condition is treated with medication, changes to diet and rest. If the vomiting becomes too severe, hospitalization with intravenous fluids and tube feeding may be necessary to prevent dehydration and help with weight gain.