In the first three months of pregnancy, only this much weight increases, if it is more then there can be trouble on the child.

how much weight should be gained in the first trimester

According to acog.org, it is normal to gain half to two and a half kilos in the first trimester. If your weight was healthy before pregnancy, then in the second and third trimester, your weight should increase by about half a kilo every week. You gain very little weight in the first trimester so no extra calories are needed at this time but you need 340 extra calories daily in the second trimester and 450 extra calories in the third trimester.

On which parts does fat accumulate in pregnancy?

According to Mayoclinic.org, the weight of the baby ranges from 3 to 3.5 kg. Your weight gain in pregnancy includes 0.5 to 1.4 kg fat on breast, 0.9 kg in uterus, 0.7 kg on placenta, 0.9 kg on amniotic fluid, 1.4 to 1.8 kg in blood volume, 0.9 to 1.4 in fluid volume, Fat stores increase by 2.7 to 3.6 kg.

If you gain more weight in the first trimester

According to lifespan.org, due to excessive weight gain during pregnancy, the baby is at risk of developing health problems. The birth weight of the baby may be more than normal and there may be some complications at the time of birth such as shoulder dystocia or preterm birth.

Symptoms of weight gain in pregnancy

If you have gained a lot of weight during pregnancy, then due to this you have difficulty in breathing, snoring or sleep apnea, heartburn, fatigue, excessive sweating and pain in the joints and back. Obesity can lead to high BP, high blood sugar and high cholesterol levels, which can also affect pregnancy.
If you eat more during pregnancy and reduce physical activity, then you may gain more weight. Anti-depressant or anti-seizure medications and certain diseases such as hypothyroidism or PCOS can also lead to obesity.

Reference:

https://www.acog.org/womens-health/experts-and-stories/ask-acog/how-much-weight-should-i-gain-during-pregnancy#:~:text=During%20your%20first %2012%20weeks,and%201%20pound%20per%20week.
https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/pregnancy-weight-gain/art-20044360
https://www.lifespan.org/centers-services/multidisciplinary-obstetric-medicine-service-moms/pregnancy-weight-gain#:~:text=Gaining%20too%20much%20weight%20during,shoulder%20dystocia%20or %20preterm%20birth.