https://www.acog.org/Patients/FAQs/Gestational-Diabetes

What is gestational diabetes?
Diabetes mellitus (also called “diabetes”) is a condition in which too much glucose (sugar) stays in the blood instead of being used for energy. Health problems can occur when blood sugar is too high. Some women develop diabetes for the first time during pregnancy. This condition is called gestational diabetes (GD). Women with GD need special care both during and after pregnancy.

How can GD affect a pregnant woman?
When a woman has GD, her body passes more sugar to her fetus than it needs. With too much sugar, her fetus can gain a lot of weight. A large fetus (weighing 9 pounds or more) can lead to complications for the woman, including
labor difficulties
cesarean delivery
heavy bleeding after delivery
severe tears in the vagina or the area between the vagina and the anus with a vaginal birth

If I have GD during pregnancy, how will I manage it?
You will need more frequent prenatal care visits to monitor your health and your fetus’s health. You will need to track your blood sugar and do things to keep it under control. Doing so will reduce the risks to both you and your fetus. For many women, a healthy diet and regular exercise will control blood sugar. Some women may need medications to help reach normal blood sugar levels even with diet changes and exercise.