The second trimester starts at the end of 12 weeks AOG (age of gestation).
I had mine at 21 weeks AOG which is a common time to get one since the baby's gender can be readily determined. And yes, since the family has had enough time guessing if the baby's a girl or a boy. And also, there is the pressing need to start buying baby stuffs and accessories by the 6th month where in knowing the baby's gender would come in handy.
But could gender be determined at a much earlier time?
The pictures here are not from my own ultrasound but ones i got from the internet.
The one on top is at 21weeks AOG which shows the baby thumb sucking which one of their common activity as in these times, reflexes are already present to help them survive life outside the womb.
In my own ultrasound, the spine is also evident and in place and during the 20-24wks of gestation, the baby undergoes a fast growth which would require a lot of vitamins and minerals essential for it.
Our OB emphasized on Calcium and Iron and had prescribed supplements for me since it was not uncommon for pregnant women to loose teeth during this period due to calcium deficiency nor develop iron-deficiency anemia during pregnancy.
The OB also checked out the baby's cardiac activity. The normal heart rate at this time is at 120 to 160 beats per minute. His heart valves are already working in sync!
Also, the placenta is already in place. It is good that I don't have a low lying placenta or placenta previa which would cause common labor complications like bleeding and/or the need for a Ceasarean section.