I offer prenatal blood work around 12 weeks, gestational diabetes screening around 28 weeks, GBS screening around 36 weeks, and additional lab work as needed. The only lab work that I require for you to be in my care is a screening for blood type and Rh factor, and screening for blood borne pathogens.
We'll discuss genetic screening at your first or second appointment. When considering genetic screening, I recommend reflecting on your family background, your race and ethnicity (some groups have higher risks of certain issues), and ultimately, what you will do with the information. Some people feel anxious unless they know that their baby is okay. Some people would terminate a pregnancy if their baby had a serious problem that would be incompatible with life. Some people would not terminate a pregnancy, no matter what. If you choose not to undergo genetic screening, you can opt for the 20 week "fetal survey" ultrasound, which will identify most problems if there are any.
If you're interested in genetic screening, I recommend Non-Invasive Prenatal Testing, a blood draw that draws fetal DNA from a pregnant parent's blood. Some people also choose this test because they want to find out the sex of the baby prior to the 20 week ultrasound. I can offer this test, or you can have it performed at a maternal-fetal medicine department of a local hospital, where you can also meet with a genetic counselor if desired.
If you're unsure of how far along you are, I would recommend going for an early ultrasound. These are most accurate in your first trimester and can help pinpoint your due date. It's not relevant information at this point in your pregnancy, but it becomes important towards the end of your pregnancy.
For example, if you're not as far along as you think, then when you're actually only 41 weeks we might think that you're 42 weeks. This can involve unnecessary stress for you and sometimes, medical intervention such as induction. On the flip side, you may be later than you realize. If someone goes into labor before 37 weeks gestation, but their provider thinks that they're beyond 37 weeks, there's a risk of them birthing a preterm baby outside of the hospital. While I'll be measuring the growth of your uterus (which roughly tracks with your weeks of pregnancy), it's helpful to have this information if you don't know when your last period was.