I visited my Ob-Gyn yesterday and as usual, we had a chitchat about our personal lives. She told me that one of her younger brothers had one child with tetralogy of Fallot and another child with truncus arteriosus. So, what are these?
Aside from being popular medicine exam questions, these are defects or problems involving the heart.
Tetralogy of Fallot (ToF) involves, of course, 4 anomalies:
1. a ventricular septal defect
2. an enlarged right ventricle
3. overriding of the aorta
4. pulmonary stenosis

Blood coming from both ventricles of the heart, a mix of oxygen-rich and oxygen-poor blood, is pumped into the circulation. Because there is lack of oxygen going through the body, those with this anomaly usually present as cyanotic or have a bluish discoloration of the skin, lips and nailbeds.
If you're interested to understand ToF better, here's a
link to a Flash video from Cincinnati Children's Hospital's website and
an article if you want to read more.
Truncus arteriosus, on the other hand, occurs due to failure of separation of a great vessel arising from the heart which should become the pulmonary artery and the aorta. This occurs with a ventricular septal defect which also causes a mixing of blood, like in ToF.

Read more on truncus arteriosus
here.
Both of these anomalies are congenital, meaning, they are present at birth. It is said to be caused by a genetic defect or due to environmental exposure during the first 8 weeks of pregnancy.
So, why did I even bother posting about this? It's to leave you a note: Take care of your embryo/fetus especially during your first trimester! If you're into drinking alcohol or coffee or are used to smoking a lot, you'd better quit while your pregnant. Encourage your partner to stop smoking as well so you and your baby won't be inhaling secondhand smoke. Watch whatever you ingest because most of it will surely go to your baby, as well.
Have a happy pregnancy!