Gestational medical conditions can be classified according to the trimester of pregnancy during which they typically occur. Here's a general classification of some common gestational medical conditions based on trimesters:

First Trimester:
1. Hyperemesis gravidarum: Severe nausea and vomiting during pregnancy that can lead to dehydration and weight loss.
2. Miscarriage: The spontaneous loss of pregnancy before the 20th week.
3. Ectopic pregnancy: A pregnancy that implants outside the uterus, typically in the fallopian tube.
4. Gestational diabetes: Diabetes that develops during pregnancy and affects blood sugar levels.
5. Thyroid disorders: Conditions such as hyperthyroidism or hypothyroidism that can occur or worsen during pregnancy.

Second Trimester:
1. Placenta previa: When the placenta covers part or all of the cervix, which can cause bleeding.
2. Gestational hypertension: High blood pressure that develops during pregnancy.
3. Preeclampsia: A condition characterized by high blood pressure, protein in the urine, and other organ dysfunction.
4. Gestational diabetes: This condition can also be diagnosed in the second trimester.
5. Preterm labor: Onset of regular contractions and cervical changes before 37 weeks of pregnancy.

Third Trimester:
1. Gestational diabetes: This condition may be diagnosed or managed in the third trimester.
2. Preeclampsia: It can develop or worsen in the third trimester.
3. Preterm labor: It can continue to occur in the third trimester.
4. Placental abruption: Premature separation of the placenta from the uterus, causing bleeding and potentially affecting fetal well-being.
5. Intrauterine growth restriction (IUGR): Poor growth of the fetus, often associated with placental insufficiency.

Please note that this classification is not exhaustive, and there can be variations in the timing and occurrence of gestational medical conditions.